JPS63263821A - Apparatus and method of reducing noise of electronic apparatus - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) Kokumei relates to a method and apparatus for reducing noise in electronic devices, more particularly noise generated during switching of output drivers used in integrated circuits. The present invention relates to a method and apparatus for reducing transient noise.

[Conventional technology]

In many electronic devices, the generation of transient noise is an undesirable result of normal operation. Although low levels of transient noise are acceptable under certain operating conditions, high levels of transient noise can render the output of an electronic device useless or cause the maximum operating conditions of the electronic device to be temporarily exceeded. It may happen. Eventually, electronic devices and devices using such electronic devices may be damaged.

Figure 1 shows an output driver 10 used in a conventional integrated circuit.
An example is shown below. This output driver 10 is driven by an input voltage v1N received from the logic of an integrated circuit (not shown) and provides an output voltage V1N used to drive an external electronic device. , yields 1.

Output driver 10 includes a first switch 14, a second switch 16, and an inductance 12 representing any internal inductance and any external inductance connected to the electronic device.

Before starting the output driver 10, the first switch 14 is closed and the second switch 16 is opened.

The power supply voltage ■DD is applied to the load capacitance 18 through the first switch 14, and the load capacitance 18 is sufficiently charged, so that the output voltage ■ of the output driver 10 is increased. UL is the power supply voltage ■. Keep it equal to D. The package inductance 12 of the integrated circuit is electrically isolated from the N source voltage DD and the load capacitance 18 by the second switch 16 which is open. Therefore, as shown in FIG. 2, the current flowing through the package inductance 2 is initially zero. Similarly, before the output driver 10 is activated, the voltage between the terminals of the package inductance is also the lowest.

11.1 At a time which can be referred to as time zero (1,), the start-up input voltage ■1- is received from the logic of the integrated circuit. In response, the ff1l switch 14 opens and the second switch 16 closes. Then, the sufficiently charged load voltage ff118 starts discharging very rapidly, and the current I
6 is supplied to the package inductance 12. Therefore, the current flowing through the package inductance 12 is ■.

The level of t increases as a step function at time t, as shown in FIG. Similarly, as shown in FIG. 3, as the load capacitance 18 discharges, the output voltage V. ol
starts to decrease.

Figure 4 shows the current I flowing through the package inductance 12.
This shows how G changes. Time t. Due to the stepwise change in current l that occurs at , the current ■. Spikes 19 occur at a rate of change of . Since the transient noise is proportional to the rate of change of the current I6 flowing through the puff cage inductance 12, the spike 19
If this occurs, transient noise at crystal level will occur, which is undesirable.

Transient noise can also be generated from several other sources. For example, when the second switch 16 begins to close, there may be a load current, I, flowing through the package inductance 12. Additionally, if at some point during the switching of the first switch 14 and the second switch 16 both switches are closed simultaneously, a crossover current may flow from the power supply through the package inductance 12, causing a transient Noise is generated.

In recent years, load capacity 18% within the same time interval as traditional drivers
What is needed is a method and apparatus for driving to higher levels of. However, if the larger value of load capacitance 18 is discharged within the same time period that the conventional capacitance value is discharged, the rate of change of current through package inductance 12 will be higher.

As a result, higher levels of transient noise are generated.

Similarly, as the level of integration becomes sharper and the number of output drivers used to drive a given capacitance increases, higher levels of transient noise will be generated.

There is also a need for a method and apparatus for reducing the time for load capacity ffi discharge. A shorter discharge time increases the rate of change of current through the package inductance, thereby increasing the level of transient switching noise generated.

To reduce transient noise, some conventional output drivers include a series of resistors connected between the load capacitance and the package inductance. However, this increases the delay time associated with the switching operation and increases the steady-state load current IL.
The resulting output voltage is upper bounded or lowered. Other conventional output drivers are the input terminal of the output driver and the previous stage theory] 11! A resistance element is included between the elements. However, this has the disadvantage of increasing the turn-on time of the output driver, reducing the number of times the output driver produces a valid output waveform.

SUMMARY OF THE INVENTION The present invention reduces optically generated noise transients during switching of output drivers of integrated circuits and other electronic devices to drive larger loads without a corresponding increase in switching time. b. provides a method and apparatus for making it possible. It has been observed that transient noise is a direct function of the rate of change of current through the package inductance of an integrated circuit. The present invention minimizes the rate of change of current by biasing the level of current flowing through the package inductance so that it assumes a substantially ramped function in time. Therefore, the rate of change (time derivative) of the ramp function is approximately constant, minimizing the level of transient noise generated. Furthermore, by selecting proper values of slope and current, no additional delay time is added to the output driver. A circuit is also disclosed that biases the current through the package inductance to approximately assume a ramp-shaped function.

The present invention is applicable to any electronic device used to drive high current devices. However, in the following description of the preferred embodiment of the invention, the invention will be described in terms of reducing transient ground noise in the output driver.

〔implementation@] Hereinafter, the present invention will be described in detail with reference to the drawings.

In the basic embodiment of the bell shown in FIG.
The output driver 20 of the present invention is a transconductance device 2
Contains 1. This transconductance device is connected between the output terminal 23 of the output driver 20 and the package inductance 22. Although the package inductance 22 represents any internal inductance or external inductance connected to the output driver, for purposes of explanation, it is assumed to be an internal inductance. Power supply voltage v
DD is also electrically connected to the output terminal 23 of the output driver 20 via the first switch 24 .

A second switch 26 is connected between the transconductance device 21 and a load resistor 29 and between the transconductance device fi21 and a grounded load capacitor 28 representing the capacitance of the electrical device being driven.

Output driver 20 initially operates in a manner similar to output driver 10 of FIG. Before starting the output driver 20, the first switch 24 is closed and the second switch 2 is closed.
6 will be opened. The supply voltage VDD is applied to the load electrical device via the closed first switch 24 to charge the load capacitance 2B. Time t. circuit (not shown)
Input voltage signal from the logic of ■l-output driver 20
When received, the first switch 24 opens and the second switch 26 closes. Therefore, the load capacitor 28 begins discharging the current 1 through the closed second switch 26. The current 11 initially increases because the load capacitor ff12B is discharged.

The transconductance device 21 of the present invention biases the current 1 discharged from the load capacitor 28 to the current 2'. This current initially has a ramp-shaped function that increases linearly in time, as shown in FIG. By biasing the current 1' during startup of the output driver 20 so that it behaves as an Ill oblique function rather than a step function, the rate of change (time derivative) of the current 2 flowing through the package inductance 22 is as shown in FIG. As shown, it is approximately constant over a certain period of time. Therefore, transient switching noise in the rate of change of current through package inductance 22 associated with the activation of output driver 20 is reduced.

FIG. 8 shows a more detailed circuit diagram of the output driver 20 of the present invention. In FIG. 8, the transconductance device 21 of FIG. 5 is replaced by a special circuit that biases the current 11 to assume a ramp function. In particular, at least a transconductance element 32 instead of the transconductance device 21, a constant current source 34, a third switch 36, a transconductance element 32 and an integrated or separate capacitance that may be provided. A capacitor 38 is used that exhibits a gate capacitance with respect to one of the two. The transconductance element 32 is coupled to provide an output current that follows the form of the voltage at the third terminal 44. First end 740 of transconductance element 32
is electrically connected to the output terminal 23 of the output driver 20, and a second terminal 42 of the transconductance element 32 is connected to the package inductance 22 of the integrated circuit. Before starting the output driver 20, the first switch 24 is closed and the power supply voltage ■ is applied. , to the load capacitor 28 to charge it. The third switch 36 is closed and the constant current source 34
A constant current 11 from the device is allowed to flow through the inductance 22 of the device. Since the voltages applied to both terminals of capacitor 38 are equal, capacitor 38 remains unchanged and the voltage applied to third terminal 44 is zero.

During startup of the output driver 20, an input voltage of 1Ntfi is received from the logic of the output circuit (not shown).

In response, the first switch 24 opens and the power supply voltage ■D
D is electrically isolated from the load capacitance 28. The third switch 36 is opened and the constant current from the constant current source 34! 1 begins charging capacitor 38 and a linearly increasing ramped voltage is applied to third terminal 44 of transconductance collector 32 .

As mentioned earlier, the mutual conductance nine 32 is the third
is configured to produce an output current having the form of a voltage at terminal 44 of . Thus, since the voltage applied to its third terminal 44 is linearly increasing, the transconductance element 32 of the present invention outputs a linearly increasing current output through its second terminal 42. Output current!
. The maximum amplitude of is the input current! 1 multiplied by the transconductance parameter Kc (having dimensions of current per unit voltage), which can be preselected by selecting an appropriate transconductance element 32.

Thus, during switching of output driver 20, linearly increasing current 16 has a constant derivative, thereby minimizing transient noise generated.

FIG. 9 shows a more detailed embodiment of the output driver 20 of the present invention in which an N-channel MOS transistor 58 is used as the transconductance element 32 of FIG. Further, a P-channel MOS transistor 54 is used in place of the first switch 24 of the output driver 20 in FIG. 8, and an N-channel MOS transistor 56 is used in place of the third switch 36. The function of second switch 26 is also performed by transistor 58.

Before the output driver 20 is activated, the input voltage signal ■IN' at the input terminal 60 of the output driver 20 is high. Therefore, P connected between the power supply voltage and the load capacitance 28
Channel transistor 54 becomes conductive, allowing power supply voltage vDD to charge load capacitance 28. The N-channel transistor 56 also becomes conductive and the power supply voltage ■
The DO and the package inductance 22 are electrically connected. Therefore, capacitor 38 remains unchanged since both terminals of the capacitor are shorted. Inverter 62 inverts the high input voltage signal v1N and then applies that voltage to the gate of Nf channel transistor 58, causing N channel transistor 56 to become nonconductive. therefore,
Package inductance 22 is electrically isolated from negative deflection 28.

When the input voltage signal ■1- becomes low, the output driver 20 is activated. Then, the N-channel transistor 56 becomes non-conductive, and the constant current from the constant current source 34 starts charging the capacitor 38. Therefore, a linearly increasing voltage is applied to the gate of N-channel transistor 58.

At the same time, P-channel transistor 54 becomes non-conductive to electrically isolate load capacitance 28 from power supply voltage DD. Therefore, the current charged in the load capacitor 28 starts to be charged through the N-channel transistor 58. N-channel transistor 58 acts as a transconductance element, biasing its output current to have the same function of time as the voltage applied to its gate. Since the frost moon is of a linearly increasing type, N-channel transistor 58 begins to flow a linearly increasing current I6 into package inductance 22. therefore,
Current ■ flowing through package inductance 22. The rate of change of is constant with respect to time to minimize the level of switching noise during power-up of the output driver.

As shown in FIG. 9, several further modifications can be made to the output driver of the present invention. First, a capacitor 64 can be provided between the input terminal of output driver 20 and the gate of N-channel transistor 58, which functions as a transconductance element. Capacitor 60 sends a charge to bias the gate of transconductance element transistor 58 to provide a gate voltage to the N-channel transistor just below the threshold of that N-channel transistor just before activating N-channel transistor 58 with an input voltage of 1N. I pretend to add it. Therefore, in order to make the N-channel transistor 58 conductive, it is only necessary to apply a very small voltage to the gate of the N-channel transistor, so the response time of the output driver 2o when the state of the input voltage 1N changes is be shortened.

The output driver 20 is a constant current source 3 shown in FIG.
Further modifications can be made by replacing 4 with another current source as shown in FIG. When the MOS transistor 58 is used as a transconductance element, the transconductance parameter K of the transconductance element. decreases with temperature, lowering the slope of the ramped current flowing through terminal 42 and increasing the switching delay time. 9th
The current source shown in the figure includes a first Pfv channel MOS transistor 66, a second P channel MOS transistor 68 whose gate and drain are short-circuited and connected as a diode, and a third P channel transistor 69. , a first N-channel MOS transistor 70 whose gate and drain are short-circuited and connected as a diode;
The drain of the first P-channel transistor has a channel MOS transistor 72 and a negative return resistor connected between the sources of the unbalanced transistors 70 and 72. 70
The drain of the second P-channel MO8 transistor 68 is connected to the drain of the second N-channel MOS transistor 72. A first P-channel MOS transistor, a second P-channel MO8 transistor 68, and a third P-channel MOS transistor 6
9 also have gates connected to the first N-channel MOS transistor 70 and the second N-channel MOS transistor 70.
It is connected in the same way as gate 2.

The sources of the first to third P-channel MOS transistors are connected to the power supply voltage, and the drain of the third MOS transistor is connected to the gate of transistor 58. The negative feedback resistor is constructed of a high temperature doped semiconductor material that exhibits a very small temperature coefficient. Unbalanced transistor 70.
72 is a mutual conductance parameter K of the mutual conductance element 32. It also includes a transconductance parameter that follows. The unbalanced transistor produces an unbalanced voltage across the terminals of negative feedback resistor 74. The transconductance parameters of unbalanced transistors 70 , 72 decrease with increasing temperature, creating an increasing unbalanced voltage across the terminals of negative feedback resistor 74 . As the voltage across the terminals of the negative feedback resistor 74 increases at high temperatures, a larger current is supplied to the capacitor 38, increasing the current per unit time applied to the terminal 44.
2 to reduce the delay time caused by temperature rise. By substituting the current source shown in FIG. 9 for current source 34 of FIG. 8, the current used to charge capacitor 38 will have a positive temperature coefficient. Therefore, capacitor 38 charges at a charging rate that increases as the temperature rises, biasing transistor 58 to flow a stable ramp current over a wide temperature range.

As can be easily seen by referring to FIG. 9, by changing only the ratio of channel width to channel length (W/L) of the third P-channel MOS transistor, the same value of package inductance and the same value of load capacitance can be obtained. The switching speed can be changed for at least one of the following. For example, if it is desired to increase the switching speed, the ratio W/L is increased and the slope shown in FIG. 6 is made steeper to increase the switching speed. Alternatively, if the W/L ratio is lowered, the slope shown in FIG. 6 becomes gentler and the switching speed becomes lower. Similarly, when the load capacitance is large or small, the W of the third P-channel MOS transistor 69
The same switching speed can be achieved by increasing or decreasing the /L ratio, respectively. Therefore, there is no need to change the geometry of the output driver for different applications. If in a particular application the package inductance is small but the switching delay time must be short, the geometry requires a high W/L ratio of the third P-channel MOS transistor 69. Only.

In another variation of the output driver of the present invention, a clamp circuit is provided to further maintain noise at a low level during start-up of the output driver 20. The output voltage ■ shown in FIG. 2 of the output driver 20 during the discharge of the load capacitor ff128. , 1 becomes lower, the transconductance parameter Kc of the transconductance device becomes smaller, regardless of what kind of transconductance device is used. Transconductance parameter K. When , the electric current output from the transconductance device becomes smaller.
! 1' decreases rapidly. As a result, the rate of change of the current, which is the derivative of the current flow, may form a negative spike 82 shown in FIG. Since the negative spike corresponds to a low voltage signal, it is a valid logic signal. but,
Negative spikes 82 will forward bias the input terminals of other electronic devices being driven by the output driver, causing them to be held up and/or to operate improperly.

The clamp 83 shown in FIG. 9 is configured to provide additional current to the package inductance 22 when the rate of change of tIo becomes negative, reducing the negative spike 82. The clamp 83 is ()channel MOS
Transistor 984 and N-channel MOS transistor 9
2, and an N-channel MOS transistor 90 whose gate and source are connected to form a diode configuration. A first P-channel MOS transistor 88, a second P-channel MOS transistor 86, a resistor 94, and a capacitor 96 are also provided. The current sources, transistors 86, 88, resistor 94, and capacitor 96 cooperate to generate a precise gate voltage of transistor 88 and the voltage across the first terminal of capacitor 96. Output voltage ■1
As □ begins to decrease, the drain voltage of transistor 88 decreases correspondingly. This voltage drop is passed across the terminals of capacitor 96. As a result, transistor 8
The precise voltage applied to the gate of 8 is reduced.

Then, the current 3 generated at the drain of the transistor 88 increases exponentially, and the rate of change of the current 6 flowing through the package inductance 22 is reduced. Thus, transistor 88 functions to detect a negative rate of change of current 16. As a result, transistor 88 becomes more conductive. When I get angry, f! voltage spike 82
An additional current 13 is supplied to the package inductance 22 to reduce . For this purpose, the output driver 5
The tendency for other electronic devices driven by 0 to be held is reduced.

As explained above, the present invention reduces transient noise generated during startup of an output driver by transmitting it to the transconductance device 2.
1, the current discharged through the package inductance is biased and linearly increased over time, thereby decreasing it. The present invention fully suppresses the transient noise caused by the cross current and the negative current I flowing through the package inductance 22 during switching. However, the present invention is illustrated in FIG. It should be noted that the present invention is not limited to the particular structure that is used. The mutual conductance device 21 is
The current discharged through the package inductance is
It encompasses all structures that can be biased linearly increasing during switching operations.

The present invention has been described above with respect to ground noise generated when an electronic device being driven is enabled to discharge through a ground inductance by a switching action.

As may be readily contemplated, the present invention may also be used to reduce or eliminate power supply switching noise generated when the electronic device being driven is first charged by a switching operation. Ideally, the power switching noise voltage and ground switching noise will be intense.

[Brief explanation of drawings]

Figure 1 is a circuit diagram showing the output driver of a conventional integrated circuit.
FIG. 2 is a graph showing the relationship between the magnitude of the current flowing through the package inductance of the conventional integrated circuit having the output driver shown in FIG. 1, its increments, and time, and FIG. Graph showing the relationship between the level of the voltage between the terminals of the package inductance and time, the fourth
The figures are graphs showing the time differentiation of the magnitude of the current flowing through the package inductance of a conventional integrated circuit having the output driver of Fig. 1, Fig. 5 is a reverse circuit diagram showing the first embodiment of the present invention, and Fig. The figure is a graph showing the relationship between the magnitude of the current flowing through the package inductance of an integrated circuit having the output driver of the present invention and time, and FIG. 7 shows the magnitude of the current flowing through the package inductance of the integrated circuit having the output driver of the present invention. 8 is a circuit diagram showing the second embodiment of the present invention, and FIG. 9 is the third embodiment of the present invention.
1 is a circuit diagram showing an embodiment of the present invention. 20.50... Output driver, 21... Mutual conductance device, 22... Package inductance,
24... First switch, 26... Second switch, 32... Mutual conductance element, 34... Constant current source, 36... Third switch.

Claims (11)

[Claims] (1) An output driver that discharges the load capacitance when activated, a package inductance representing the inductance of the integrated circuit, an input current flowing through the package inductance received from the load capacitance that is being discharged while the output driver is activated, and the load capacitance. a switch of the integrated circuit for driving the current load; 1. A device for reducing noise in an electronic device, characterized in that the level of transient noise is reduced. (2) further comprising a linearly increasing voltage, the biasing means including a transconductance element, a first terminal of the transconductance element being electrically connected to a load capacitance through which the input current flows; A linearly increasing voltage can be applied to a second terminal of the element, and a third terminal of the transconductance element is electrically connected to a package inductance of an integrated circuit;
Claims characterized in that the transconductance element biases the current applied to its first terminal to assume the same linearly increasing form as the voltage applied to its second terminal. A device for reducing noise in an electronic device according to paragraph (1). (3) The biasing means includes a capacitor having a first terminal electrically connected to a second terminal of the transconductance element, and a second terminal, and charging the capacitor with a constant current during startup of the output driver. a constant current source connected to the second terminal of the capacitor for generating a linearly increasing voltage applied to the second terminal of the transconductance element. A device for reducing noise in an electronic device according to scope (2). (4) The constant current source includes a pair of unbalanced transistors and a resistor, and when the temperature rises, the unbalanced transistor increases the voltage between the terminals of the resistor to bias the constant current source and supply it to the second terminal of the capacitor. A device for reducing noise in an electronic device as claimed in claim 3, characterized in that the device increases the current applied to the electronic device. (5) The transconductance element is a MOS transistor having a gate, a source, and a drain. The gate is the second terminal of the transconductance element to which a linearly increasing voltage is applied, and the source is electrically connected to the load capacitance. Claim 2, characterized in that the source is a third terminal of the transconductance element electrically connected to the package inductance of the integrated circuit. ) A device for reducing noise in an electronic device according to item 2. (6) the MOS transistor has a threshold voltage that biases the MOS transistor to make it conductive; the biasing means further includes a capacitor;
Reducing noise in an electronic device according to claim (5), characterized in that charge is supplied to the gate of the MOS transistor at a predetermined level lower than the threshold voltage of the MOS transistor before the OS transistor becomes conductive. device to do. (7) The process of providing a load capacitor that discharges current through the package inductance during startup of the output driver, and biasing the current discharged from the load capacitance to take a nearly linear increasing function during startup of the output driver. 1. A method for reducing noise in an electronic device, comprising: reducing the level of transient noise generated during startup of an output driver of an integrated circuit having a package inductance. (8) The biasing process includes the steps of providing a transconductance element, generating a voltage function that increases almost linearly over time, and applying the voltage function that increases approximately linearly to the second terminal of the transconductance element. a first terminal of the transconductance element is electrically connected to a load capacitance through which the input current flows, and a linearly increasing voltage is applied to the second terminal of the transconductance element. A third terminal of the transconductance element may be electrically connected to a package inductance of an integrated circuit, and the transconductance element biases a current applied to its first terminal to a second terminal. A method for reducing noise in an electronic device according to claim 7, characterized in that the voltage applied to the terminals is of the same linearly increasing form. (9) The process of generating a voltage function that increases approximately linearly includes the steps of providing a capacitor to be discharged first, and supplying a constant value of current to one terminal of the capacitor to be discharged first. A method for reducing noise in an electronic device according to claim 8, characterized in that: (10) further comprising a current clamp, the current clamp having a power supply voltage, a gate, a source connected to the power supply voltage, and a drain connected to the package inductance;
a second MOS transistor having the same conductivity type as that of the first MOS transistor and having a gate, a source connected to a power supply voltage, and a drain connected to the gate like a diode;
an S transistor, a resistor connected between the drain of the second MOS transistor and the gate of the first MOS transistor, a capacitor connected between the gate of the first MOS transistor and the package inductance, and the second MOS transistor. a current source connected between the gate and drain of the transistor, the current clamp detecting a current transient that decreases as a result of a decrease in charge in the load capacitance and supplies additional instantaneous current to the package inductance. A device for reducing noise in an electronic device as claimed in claim (1). (11) further comprising a current, the constant current source includes a MOS transistor, the MOS transistor has a characteristic channel width/
This MOS transistor provides a bias current from the power supply to the second terminal of the capacitor, which drives the switching speed of the integrated circuit by changing the characteristic channel width/channel length ratio of the MOS transistor. The driving current load can be increased for the same value of the current load driven, and the value of the driven current load can be changed for the same switching speed. A device that reduces noise in electronic devices.