CN103731151B - Method and circuit for converting duty ratio into analog signal - Google Patents
Method and circuit for converting duty ratio into analog signal Download PDFInfo
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- CN103731151B CN103731151B CN201410017698.8A CN201410017698A CN103731151B CN 103731151 B CN103731151 B CN 103731151B CN 201410017698 A CN201410017698 A CN 201410017698A CN 103731151 B CN103731151 B CN 103731151B
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Abstract
Disclose the circuit and method for converting duty ratio into analog signal.The circuit includes：Duty ratio measuring unit, for receiving switch controlling signal, and obtains the digital value of the dutycycle relevant parameter of switch controlling signal；And D/A conversion unit, the digital value for receiving dutycycle relevant parameter, and the digital value of dutycycle relevant parameter is converted into analog signal.The circuit can reduce cost and improve transient response speed.
Description
Technical field
The present invention relates to electronic technology field, more particularly to the method and electricity for converting duty ratio into analog signal
Road.
Background technology
Switching Power Supply generally includes power stage circuit and control circuit.The function of controlling circuit is in input voltage, inside
When parameter and external load change, the turn-on and turn-off time of the switching system in regulation power stage circuit, so that Switching Power Supply
Output voltage or output current keep it is constant.
The control mode of Switching Power Supply can be divided into fixed-frequency control and VFC.Fixed-frequency control is that switch periods are constant not
Become, output voltage, i.e. pulse width modulation are adjusted by adjusting the time width of switch conduction in a cycle（PWM）.Become
The frequency of the i.e. switch of frequency control changes with the amplitude of input signal, i.e. pulse frequency modulated（PFM）.Pulse frequency modulated
（PFM）, there is constant on-time, constant off-time and sluggishness to compare the control modes such as control for it.
In Switching Power Supply, the Part I of control circuit is compared output voltage or output current with sawtooth signal
Compared with so as to produce the pwm signal or PFM signals with dutycycle.The Part II of circuit is controlled to receive pwm signal or PFM letters
Number as input signal, control signal is then produced, for the switch conduction in power switched level circuit or disconnection.It will can control
The Part II and power stage circuit of circuit processed regard duty cycle conversion circuit as together.The duty cycle conversion circuit believes PWM
Number or PFM signals be converted into the VD or DC output power of analog signal, i.e. Switching Power Supply.
Duty cycle conversion circuit is also widely used for various analog measurement instrument or load drive device.Measured in simulation
Measure in instrument, for example, need pwm signal being converted into analog voltage or current signal.In load drive device, for example, need
Voltage or electric current by loading is adjusted according to the pwm signal of outside input.It is used as load drive device, duty cycle conversion circuit
Light emitting diode can be realized（LED）Simulation light modulation, the simulation speed governing of radiator fan or power adjusting etc. of amplifier.
Although being frequently utilized that digital circuit generation pwm signal or PFM signals, duty cycle conversion circuit itself is still bag
The analog circuit in the loop containing resistance capacitance.For the analog signal of smooth output end, the time constant in resistance capacitance loop is necessary
The frequency of long-range switch controlling signal.This volume for not only resulting in integrated circuit and cost increase, and cause duty cycle conversion
The transient response of circuit is slow.
Therefore, it is desirable to further reduce the cost of duty cycle conversion circuit and improve transient response speed.
The content of the invention
In view of this, it is an object of the invention to provide a kind of low cost and the fast duty cycle conversion circuit of transient response.
According to the first aspect of the invention there is provided a kind of circuit for being used to convert duty ratio into analog signal, including：Account for
Sky for receiving switch controlling signal, and obtains the numeral of the dutycycle relevant parameter of switch controlling signal than measuring unit
Value；And D/A conversion unit, the digital value for receiving dutycycle relevant parameter, and by the numeral of dutycycle relevant parameter
Value is converted into analog signal.
Preferably, in the circuit, the dutycycle relevant parameter includes the ON time of switch controlling signal, shut-off
At least one in time and Cycle Length.
Preferably, in the circuit, the analog signal includes one kind in DC current and DC voltage.
Preferably, in the circuit, the duty ratio measuring unit includes：Rising edge and trailing edge detector, are used for
Receive switch controlling signal, and switch controlling signal Square wave pulses rising edge and trailing edge produce it is corresponding synchronous
Trigger signal；Counter, for being counted under the control of synchronous triggering signal to clock signal；And register, it is used for
Count value is exported from counter count pick up value, and under the control of synchronous triggering signal.
Preferably, in the circuit, the duty ratio measuring unit also includes：With door, believe for receiving switch control
Number and clock signal, and only switch controlling signal the high level stage to counter export clock pulses.
Preferably, in the circuit, the duty ratio measuring unit also includes：NOT gate, for receiving switch control letter
Number and output switch control signal inversion signal；And with door, inversion signal and clock for receiving switch controlling signal
Signal, and only switch controlling signal the low level stage to counter export clock pulses.
Preferably, in the circuit, the clock signal is produced by external circuit.
Preferably, the circuit also includes：Oscillator, for producing the clock letter under the control of synchronous triggering signal
Number.
Preferably, in the circuit, the duty ratio measuring unit includes also including shift register, for by described in
The digital value displacement of register output.
Preferably, in the circuit, the dutycycle relevant parameter includes ON time and the week of switch controlling signal
Phase length, also, the shift register is identical with the count value displacement of Cycle Length by the ON time of switch controlling signal
Digit.
Preferably, in the circuit, the dutycycle relevant parameter includes the turn-off time and week of switch controlling signal
Phase length, also, the shift register is identical with the count value displacement of Cycle Length by the turn-off time of switch controlling signal
Digit.
Preferably, in the circuit, the D/A conversion unit includes digital analog converter, for by the dutycycle phase
Related parameter is converted to corresponding analog signal.
Preferably, in the circuit, the D/A conversion unit includes：Dutycycle computing module, for being accounted for from described
Sky calculates the digital value of dutycycle than relevant parameter；And digital analog converter, for the digital value of the dutycycle to be changed
Into corresponding analog signal.
Preferably, in the circuit, the D/A conversion unit includes：Digital analog converter, for by the dutycycle
Relevant parameter is converted to the first resistor value for representing ON time and the second resistance value for representing Cycle Length；Current feedback circuit,
For producing reference current according to second resistance value；And voltage generator, for according to first resistor value and reference current production
Raw analog signal.
According to the second aspect of the invention there is provided a kind of method for converting duty ratio into analog signal, including：Connect
Receive switch controlling signal；Obtain the digital value of the dutycycle relevant parameter of switch controlling signal；And by dutycycle relevant parameter
Digital value be converted into analog signal.
Preferably, in the process, the dutycycle relevant parameter includes the ON time of switch controlling signal, shut-off
At least one in time and Cycle Length.
Preferably, in the process, the analog signal includes one kind in DC current and DC voltage.
Preferably, in the process, the step of digital value for the dutycycle relevant parameter for obtaining switch controlling signal, wraps
Include：Corresponding synchronous triggering signal is produced in the rising edge and trailing edge of the Square wave pulses of switch controlling signal；Synchronously touching
Clock signal is counted under the control of signalling；And export count value under the control of synchronous triggering signal.
Preferably, in the process, only in the high level stage of switch controlling signal, in the control of synchronous triggering signal
Under clock signal is counted.
Preferably, in the process, only in the low level stage of switch controlling signal, in the control of synchronous triggering signal
Under clock signal is counted.
Preferably, in the process, in the whole cycle of switch controlling signal, under the control of synchronous triggering signal
Clock signal is counted.
Preferably, in the process, the step of digital value for the dutycycle relevant parameter for obtaining switch controlling signal, wraps
Include：Obtain the ON time of switch controlling signal and the count value of Cycle Length；And by the ON time of switch controlling signal
Identical digit is shifted with the count value of Cycle Length.
Preferably, in the process, the step of digital value for the dutycycle relevant parameter for obtaining switch controlling signal, wraps
Include：Obtain the turn-off time of switch controlling signal and the count value of Cycle Length；And by the turn-off time of switch controlling signal
Identical digit is shifted with the count value of Cycle Length.
Preferably, in the process, the step of digital value of dutycycle relevant parameter being converted into analog signal includes：
The digital value of dutycycle is calculated from the dutycycle relevant parameter；And be converted into the digital value of the dutycycle accordingly
Analog signal.
Preferably, in the process, the step of digital value of dutycycle relevant parameter being converted into analog signal includes：
The dutycycle relevant parameter is converted to the first resistor value for representing ON time and the second resistance value for representing Cycle Length；
Reference current is produced according to second resistance value；And analog signal is produced according to first resistor value and reference current.
The duty cycle conversion circuit of the present invention is Digital Analog Hybrid Circuits, will switch control using duty ratio measuring unit first
Signal is converted into digital value, then produces analog signal according to the digital value using D/A conversion unit.Therefore, in output stage not
The resistance and output capacitance using big numerical value are needed, so that chip area is reduced, so as to reduce duty cycle conversion circuit
Cost.The duty cycle conversion circuit can realize the rapid translating from dutycycle to analog signal.Only in a signal period
Interior, the output end of the duty cycle conversion circuit can just reflect the change of input signal, so as to improve transient response speed.
Brief description of the drawings
By description referring to the drawings to the embodiment of the present invention, above-mentioned and other purposes of the invention, feature and
Advantage will be apparent from, in the accompanying drawings：
Fig. 1 shows the schematic circuit of the duty cycle conversion circuit according to prior art；
Fig. 2 shows the schematic block diagram of the duty cycle conversion circuit according to the present invention；
Fig. 3 shows the flow chart of the duty cycle conversion method according to the present invention；
Fig. 4 show according to the present invention duty cycle conversion circuit in duty ratio measuring unit first embodiment it is schematic
Block diagram；
Fig. 5 show according to the present invention duty cycle conversion circuit in duty ratio measuring unit second embodiment it is schematic
Block diagram；
Fig. 6 show according to the present invention duty cycle conversion circuit in duty ratio measuring unit 3rd embodiment it is schematic
Block diagram；
Fig. 7 show according to the present invention duty cycle conversion circuit in duty ratio measuring unit fourth embodiment it is schematic
Block diagram；
Fig. 8 shows the timing diagram of pwm signal and external timing signal in the duty cycle conversion circuit according to the present invention；
Fig. 9 shows the schematic frame of the first embodiment of D/A conversion unit in the duty cycle conversion circuit according to the present invention
Figure；
Figure 10 show according to the present invention duty cycle conversion circuit in D/A conversion unit second embodiment it is schematic
Block diagram；And
Figure 11 show according to the present invention duty cycle conversion circuit in D/A conversion unit second embodiment it is schematic
Block diagram.
Embodiment
The preferred embodiments of the present invention are described in detail below in conjunction with accompanying drawing.Those of ordinary skill in the art should manage
Solution, accompanying drawing is provided to the purpose of explanation provided herein, and accompanying drawing is not necessarily drawn to scale.In order to avoid obscuring
The essence of the present invention, known method, process, flow, element and circuit do not have detailed narration.
It should be appreciated that when claiming element " being couple to " or " being connected to " another element, it can be direct coupling or connect
To another element or there may be intermediary element, the connection between element can be physically, in logic or its knot
Close.On the contrary, when claiming element " being directly coupled to " or " being directly connected to " another element, it is meant that cental element is not present in both
Part.
In this application, term " switch controlling signal " refers to rectangular wave pulse signal, in the every of rectangular wave pulse signal
The individual cycle includes a high level stage and a low level stage.Term " dutycycle " refers in rectangular wave pulse signal
In a cycle, ON time Ton（For example, in a cycle high level signal duration）With rectangular wave pulse signal
Switch periods T（That is, the length of a cycle）Ratio, represented by symbol D.Term " duty ratio measuring unit " refers to be used to survey
The amount parameter related to the dutycycle of rectangular wave pulse signal（Such as ON time TON, turn-off time TOFFAnd/or switch periods
T）Circuit module.
Fig. 1 shows the schematic circuit of conventional duty cycle conversion circuit 10.The duty cycle conversion circuit 10 includes anti-
Phase device A1, upper switching tube S1, lower switching tube S2, resistance R1, output capacitance C1.Upper switching tube S1, lower switching tube S2, resistance R1,
Output capacitance C1 constitutes power stage circuit 11 together.
In duty cycle conversion circuit 10, upper switching tube S1 and lower switching tube S2 are connected in series in reference voltage VREFAnd ground
Between.The input of duty cycle conversion circuit 10 receives pwm signal.Then, pwm signal provides supreme switching tube S1 control
Hold, and pwm signal is provided to lower switching tube S2 control end via phase inverter A1 so that upper switching tube S1 and lower switching tube S2
Alternate conduction and disconnection.Resistance R1 is serially connected between switching tube S1 and lower switching tube S2 node and output end.Output capacitance
C1 is connected between output end and ground.
When the pwm signal of input is high level, the control signal for being applied directly to switching tube S1 control end is height
Level, the control signal of inverted anti-phase after-applied to the lower switching tube S2 of device A1 control end is low level, so that upper switching tube
S1 is turned on, and lower switching tube S2 disconnects.Reference voltage VREFOutput capacitance C1 is charged via upper switching tube S1 and resistance R1.Conversely,
When the pwm signal of input is low level, the control signal for being applied directly to switching tube S1 control end is low level, through anti-
The control signal of anti-phase after-applied to the lower switching tube S2 of phase device A1 control end is high level, so that upper switching tube S1 disconnects, under
Switching tube S2 is turned on.Output capacitance C1 discharges over the ground via resistance R1 and lower switching tube S2.
Because resistance R1 and output capacitance C1 have smoothing effect for pulse input, in the control of continuous pwm signal
Under, the output of duty cycle conversion circuit 10 is smooth dc voltage and DC current that component is superimposed with minimum ripple.If
Voltage V of resistance R1 and output capacitance the C1 time constant much larger than input PWM signal frequency, then output endout=VREF* D, its
Middle D=TON/ T, TONFor the ON time in a cycle, T is the length of a cycle.
The shortcoming of above-mentioned conventional duty cycle conversion circuit 10 is that resistance R1 and output capacitance C1 time constant are necessary
Much larger than the frequency of pwm signal, voltage V just can ensure thatoutIt is approximately direct current signal.As a result, resistance R1 and output capacitance C1 number
Value must be larger, and this can increase cost in integrated circuit design, or even can not realize at all.Also, due to time constant
Presence, this method dynamic adjustment it is very slow, the change of switch controlling signal, which takes long enough to reflect, arrives Vout。
Fig. 2 shows the schematic block diagram of the duty cycle conversion circuit 100 according to the present invention, and Fig. 3 is shown according to the present invention's
The flow chart of duty cycle conversion method.The duty cycle conversion circuit 100 includes duty ratio measuring unit 110, D/A conversion unit
120。
The input of duty cycle conversion circuit 100 receives pwm signal or PFM signals (step S01).For each week
Phase, duty ratio measuring unit 110 measures the parameter related to dutycycle, and exports its digital value（Step S02）.In the application
In, the parameter related to dutycycle includes ON time TON, turn-off time TOFF, at least one parameter in Cycle Length T.Number
Mould converting unit 120 receives the digital value of the parameter, and converts digital values into the amplitude simulation corresponding with dutycycle
Output signal（Step S03）.In one example, the voltage V of the output end of duty cycle conversion circuit 100out=k*D, wherein k are
Constant.
It should be noted that the duty cycle conversion circuit 100 of the present invention is Digital Analog Hybrid Circuits, first using duty ratio measuring list
Switch controlling signal is converted into digital value by member 110, then produces simulation letter according to the digital value using D/A conversion unit 120
Number.Therefore, the resistance and output capacitance of big numerical value need not be used in output stage, this not only lowers duty cycle conversion circuit
100 cost, and improve transient response speed.
Fig. 4 to 7 shows some embodiments of duty ratio measuring unit in the duty cycle conversion circuit 100 according to the present invention
Schematic block diagram, Fig. 8 shows the sequential of pwm signal and external timing signal in the duty cycle conversion circuit 100 according to the present invention
Figure.
Referring to Fig. 4, according to the duty ratio measuring unit 110 of first embodiment include rising edge and trailing edge detector 111,
With door 112, counter 113, register 114.
The input of duty ratio measuring unit 110 receives switch controlling signal（Pwm signal for example shown in Fig. 8）And outside
Clock signal clk（Clock signal clk for example shown in Fig. 8）.In order to obtain suitable counting precision, external timing signal CLK
Frequency fCLKThe frequency f of switch controlling signal should be significantly greater thanPWM.For example, fCLK>100*fPWM。
Switch controlling signal is provided to rising edge and trailing edge detector 111.In each cycle of switch controlling signal,
Rising edge and trailing edge detector 111 detect the rising edge and trailing edge of the signal, to obtain the high level stage at the beginning of carve
T0 and its finish time t1.Start time t0 not only represents the beginning in high level stage, and represents the end in previous cycle
With the beginning of current period.In moment t0 and t1, rising edge and trailing edge detector 111 produce corresponding synchronous triggering signal,
And provide synchronous triggering signal to counter 113 and register 114.
In addition, by switch controlling signal and external timing signal CLK provide together to door 112.In switch controlling signal
Each cycle, with door 112 only switch controlling signal the high level stage export clock pulses.The output clock pulses is carried
It is supplied to counter 113.Under the control of synchronous triggering signal, counter 113 resets and started counting up in moment t0, in moment t1
Stop counting, and count value is stored in register 114, then export the digital value T of ON timeON。
Referring to Fig. 5, according to the duty ratio measuring unit 210 of second embodiment include rising edge and trailing edge detector 211,
With door 212, counter 213, register 214, NOT gate 215.
It is different from the duty ratio measuring unit 110 shown in Fig. 4, in the duty ratio measuring unit 210 according to second embodiment
In, switch controlling signal is provided to NOT gate 215.The inversion signal of the output switch control signal of NOT gate 215.Then, it will switch
The inversion signal and external timing signal CLK of control signal provide together to door 212.In each week of switch controlling signal
Phase, only clock pulses is exported in the low level stage of switch controlling signal with door 212.The output clock pulses is provided to counting
Device 213.Under the control of synchronous triggering signal, counter 213 resets and started counting up in moment t1, in the beginning in next cycle
Moment t2 stops counting, and count value is stored in into register 214, then exports the digital value T of turn-off timeOFF。
The other parts of the duty ratio measuring unit 210 and the appropriate section phase of the duty ratio measuring unit 110 shown in Fig. 4
Together.
Referring to Fig. 6, according to the duty ratio measuring unit 310 of 3rd embodiment include rising edge and trailing edge detector 311,
Counter 312, register 313.
It is different from the duty ratio measuring unit 110 shown in Fig. 4, in duty ratio measuring unit 310, by external timing signal
CLK is provided directly to counter 312.Clock pulses is exported in the whole cycle of switch controlling signal.In synchronous triggering signal
Control under, counter 312 resets and started counting up in moment t0, at the beginning of next cycle carve t2 stop count, and
Count value is stored in register 313, the digital value T of Cycle Length is then exported.
The other parts of the duty ratio measuring unit 310 and the appropriate section phase of the duty ratio measuring unit 110 shown in Fig. 4
Together.
ON time in each cycle of switch controlling signal is being obtained respectively described above is duty ratio measuring unit
Digital value TON, in each cycle the turn-off time digital value TOFFOr the digital value T of the Cycle Length in each cycle different implementations
Example.However, these embodiments can be combined as needed, to form new duty ratio measuring unit.
For example, with reference to Fig. 7, rising edge is included according to the duty ratio measuring unit 410 of fourth embodiment and trailing edge is detected
Device 411 and door 412, counter 413, register 414, counter 416, register 417.The duty ratio measuring unit 410 can be with
The combination for the duty ratio measuring unit 310 being considered shown in duty ratio measuring unit 110 and Fig. 6 shown in Fig. 4.As preferred
Embodiment, duty ratio measuring unit 410 also includes additional shift register 415 and 418.
The input of duty ratio measuring unit 410 receives switch controlling signal（Pwm signal for example shown in Fig. 8）And outside
Clock signal clk（Clock signal clk for example shown in Fig. 8）.In order to obtain suitable counting precision, external timing signal CLK
Frequency fCLKThe frequency f of switch controlling signal should be significantly greater thanPWM.For example, fCLK>100*fPWM。
Switch controlling signal is provided to rising edge and trailing edge detector 411.In each cycle of switch controlling signal,
Rising edge and trailing edge detector 411 detect the rising edge and trailing edge of the signal, to obtain the high level stage at the beginning of carve
T0 and its finish time t1.Start time t0 not only represents the beginning in high level stage, and represents the end in previous cycle
With the beginning of current period.In moment t0 and t1, rising edge and trailing edge detector 411 produce corresponding synchronous triggering signal,
And provide synchronous triggering signal to counter 413, register 414, counter 416, register 417 and optional displacement
Register 415 and 418.
In addition, by switch controlling signal and external timing signal CLK provide together to door 412.In switch controlling signal
Each cycle, only switch controlling signal the high level stage export clock pulses.The output clock pulses is provided to meter
Number device 413.Under the control of synchronous triggering signal, counter 413 resets and started counting up in moment t0, stops counting in moment t1
Number, and count value is stored in register 414, then export the digital value T of ON timeON。
In addition, external timing signal CLK is provided directly into counter 416.In the whole cycle of switch controlling signal
Export clock pulses.Under the control of synchronous triggering signal, counter 416 resets and started counting up in moment t0, in next week
T2 is carved at the beginning of phase to stop counting, and count value is stored in register 417, then exports the digital value T of Cycle Length.
In a preferred embodiment, by the count value T of ON timeONThere is provided to shift register 415, and will the cycle it is long
The count value T of degree is provided to shift register 418.If the highest significant position for detecting the count value of Cycle Length is not equal to 1,
Then in shift register 415 and 418, the count value of ON time and the count value of Cycle Length are shifted into identical digit,
And ensure Cycle Length digital value T highest significant position be 1, the count value after displacement is used as the digital value that will be exported.With
Afterwards, by the digital value T according to ON timeONWith the digital value T of Cycle Length ratio calculation dutycycle.This normalization operation
Real dutycycle can be obtained, and calculation error can be reduced.
In a preferred embodiment, duty ratio measuring unit can include internal oscillator to produce clock signal clk, from
And replace external timing signal CLK.Rising edge and trailing edge detector 411 further provide trigger signal for internal oscillator.
Under the control of lock-out pulse, internal oscillator moment t0 reset with produce with the rising edge alignment of switch controlling signal when
Clock, resets to produce the clock pulses alignd with the trailing edge of switch controlling signal in moment t1, so as to provide more
Plus accurate count results.
Fig. 9 to 11 shows some embodiments of D/A conversion unit in the duty cycle conversion circuit 100 according to the present invention
Schematic block diagram.
Referring to Fig. 9, digital analog converter 121 is included according to the D/A conversion unit 120 of first embodiment.
The input of digital analog converter 121 receives the digital value T of ON timeON, such as from the duty ratio measuring list shown in Fig. 4
The output end of member 110 receives TON.Then, the digital value is converted into corresponding analog signal by digital analog converter 121：VOUT=VREF*
TON, wherein VREFIt is the reference voltage of digital analog converter 121.If switch controlling signal is the pwm signal of frequency-invariant, count
The output V of mould converting unit 120OUTIt is proportional to dutycycle D：VOUT=k*D, wherein k are constant.
Referring to Figure 10, dutycycle computing module 221 is included according to the D/A conversion unit 220 of second embodiment and digital-to-analogue turns
Parallel operation 222.
The input of dutycycle computing module 221 receives the digital value T of ON timeONWith the digital value T of Cycle Length, example
The output end of duty ratio measuring unit 410 as shown in from Fig. 7 receives TONAnd T.Then, dutycycle computing module 221 according to etc.
Formula D=TON/ T, calculates dutycycle D digital value.In alternate embodiments, the input of dutycycle computing module 221 is received
Turn-off time TOFFDigital value and Cycle Length T digital value.Then, dutycycle computing module 221 is according to equation D=1-TOFF/
T, calculates dutycycle D digital value.
The input of digital analog converter 222 receives dutycycle D digital value, is then converted into corresponding simulation letter
Number：VOUT=VREF* D, wherein VREFIt is the reference voltage of digital analog converter 222.As a result, no matter switch controlling signal is frequency-invariant
Pwm signal or changeable frequency PFM signals, the output V of D/A conversion unit 222OUTIt is proportional to dutycycle D.
Referring to Figure 11, digital analog converter 321 and 322, electric current are included according to the D/A conversion unit 320 of 3rd embodiment and sent out
Raw device 323 and voltage generator 324.
The input of digital analog converter 321 and 322 receives the digital value T of ON time respectivelyONWith the numeral of Cycle Length
Value T, for example, receive T from the output end of the duty ratio measuring unit 410 shown in Fig. 7ONAnd T.
Then, digital analog converter 321 is by the digital value T of ON timeONBe converted to corresponding first resistor value：RTON=Ε
ni·2iR, wherein niIt is 0 or 1 for the digital value of i-th bit；And R is a fixed resistance value.
If for example, the digital value T of ON timeONFor octet 1000,1000, then
Similarly, the digital value T of Cycle Length can be converted to second resistance value RT。
Then, second resistance value RT is provided to current feedback circuit 323, produces reference current IREF：Its
Middle VREFIt is the reference voltage of current feedback circuit 323.
Then, by first resistor value RTonWith reference current IREFThere is provided to voltage generator 324.Voltage generator 324 is produced
Raw output analog voltage：VOUT=VREF* D, wherein VREFIt is the reference voltage of current feedback circuit 323.As a result, no matter switch control is believed
Number it is the pwm signal of frequency-invariant or the PFM signals of changeable frequency, in each cycle of switch controlling signal, voltage hair
The output V of raw device 324OUTIt is proportional to dutycycle D.
The duty cycle conversion circuit and its method of output analog voltage is described above.In alternative embodiment,
Duty cycle conversion circuit may further include additional converter, and output analog voltage is converted into exporting mould
Intend electric current.LED driver may be used as according to the duty cycle conversion circuit of the alternate embodiment.For example in LED driver, root
LED driving current is adjusted according to pwm signal, to realize simulation light modulation（analog dimming）.
According to embodiments of the invention as described above, these embodiments do not have all details of detailed descriptionthe, not yet
It is only described specific embodiment to limit the invention.Obviously, as described above, it can make many modifications and variations.This explanation
Book is chosen and specifically describes these embodiments, is in order to preferably explain the principle and practical application of the present invention, so that affiliated
Technical field technical staff can be used using modification of the invention and on the basis of the present invention well.The present invention is only by right
The limitation of claim and its four corner and equivalent.
Claims (9)
1. a kind of circuit for being used to convert duty ratio into analog signal, including：
Duty ratio measuring unit, for receiving switch controlling signal, and obtains ON time and the cycle of switch controlling signal
The digital value of length；
Dutycycle computing module, the digital value for calculating dutycycle from the digital value of the ON time and Cycle Length；
And
Digital analog converter, for the digital value of the dutycycle to be converted into analog signal,
Wherein, the duty ratio measuring unit includes：
Rising edge and trailing edge detector, for receiving switch controlling signal, and in the Square wave pulses of switch controlling signal
Rising edge and trailing edge produce corresponding synchronous triggering signal；
Counter, for being counted under the control of synchronous triggering signal to clock signal, to obtain ON time and cycle
The count value of length；
Register, the count value for receiving the ON time and Cycle Length from counter, and in synchronous triggering signal
Control under export count value；And
Shift register, for the count value of the ON time and Cycle Length to be shifted into identical digit, so that the week
The highest significant position of the count value of phase length is 1, obtains the digital value of the ON time and Cycle Length.
2. circuit according to claim 1, wherein the analog signal includes one kind in DC current and DC voltage.
3. circuit according to claim 1, wherein the duty ratio measuring unit also includes：
With door, for receiving switch controlling signal and clock signal, and only switch controlling signal the high level stage to meter
Number device output clock pulses.
4. circuit according to claim 1, wherein the duty ratio measuring unit also includes：
NOT gate, the inversion signal for receiving switch controlling signal and output switch control signal；And
With door, inversion signal and clock signal for receiving switch controlling signal, and only in the low electricity of switch controlling signal
The flat stage exports clock pulses to counter.
5. circuit according to claim 1, the clock signal is produced by external circuit.
6. circuit according to claim 1, in addition to：
Oscillator, for producing the clock signal under the control of synchronous triggering signal.
7. a kind of method for converting duty ratio into analog signal, including：
Receive switch controlling signal；
Corresponding synchronous triggering signal is produced in the rising edge and trailing edge of the Square wave pulses of switch controlling signal；
Clock signal is counted under the control of synchronous triggering signal, to obtain the counting of ON time and Cycle Length
Value；
Count value is exported under the control of synchronous triggering signal；
The count value of the ON time and Cycle Length is shifted into identical digit, so that the count value of the Cycle Length
Highest significant position is 1, obtains the digital value of the ON time and Cycle Length；
The digital value of dutycycle is calculated from the digital value of the ON time and Cycle Length；And
The digital value of the dutycycle is converted into corresponding analog signal.
8. method according to claim 7, wherein the analog signal includes one kind in DC current and DC voltage.
9. method according to claim 7, wherein in the whole cycle of switch controlling signal, in synchronous triggering signal
Clock signal is counted under control.
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