JPH08125531A - Frequency synthesizer circuit - Google Patents

Abstract

PURPOSE: To provide a frequency synthesizer circuit which can inhibit the phase fluctuation of an RF modulation signal owing to disturbance and whose modulation accuracy is satisfactory. CONSTITUTION: An offset signal generation circuit 4 generate offset voltage for dissolving the fluctuation of the frequency by the disturbance signal based on the disturbance signal becoming a cause for fluctuating the frequency of a local oscillation signal being the output of a voltage control oscillator 6. An offset signal addition circuit 5 adds offset voltage from the offset signal generation circuit 4 to turning voltage and supplies it to the voltage control oscillator 6.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a frequency synthesizer circuit mounted on a communication device typified by a digital mobile communication device for performing communication using a plurality of time-divided communication slots. It is a thing.

[0002]

2. Description of the Related Art As shown in FIG. 5, a conventional frequency synthesizer circuit mounted in a communication device for performing communication using a plurality of time-divided communication slots has a reference oscillator 3 as shown in FIG.
1, the phase comparator 32, the low pass filter 33, the voltage controlled oscillator 34, the mixer 35, and the comparison frequency divider 36. The reference oscillator 31 generates a frequency signal that serves as a reference for the frequency switching width of the frequency synthesizer circuit, and outputs it to the phase comparator 32. The phase comparator 32 detects a phase difference between the frequency signal from the reference oscillator 31 and the frequency-divided output signal from the comparison frequency divider 36, and supplies a voltage according to the phase difference to the low-pass filter 33. The low pass filter 33 integrates the voltage from the phase comparator 32 and outputs it as a tuning voltage to the voltage controlled oscillator 34. The voltage controlled oscillator 34 generates a frequency signal according to the tuning voltage from the low pass filter 33, and outputs it as a local oscillation signal to the mixer 35 and the comparison frequency divider 36. The power supply of the mixer 35 is controlled by the burst power supply control signal, and based on the local oscillation signal and the IF modulation signal from the voltage controlled oscillator 34, the mixer 35 outputs the RF modulation signal only in the burst period. The comparison frequency divider 36 frequency-divides the local oscillation signal from the voltage controlled oscillator 34 according to the frequency division ratio data from the control unit (not shown), and outputs the frequency division output to the phase comparator 32.

As shown in FIG. 6, the mixer 35 has a buffer 38, a mixer section 39, and an amplifier 40.

[0004]

Generally, in a mobile station,
In order to reduce current consumption, circuits that do not need to be energized are turned off during periods when neither transmission nor reception is performed. Turning on / off of the power source is controlled by a burst power source control signal as shown in FIG. By the way, as a recent configuration of the mixer 35, as described above,
In addition to the mixer section 39, a buffer 38 is provided between the local oscillation signal input end and the mixer section 39, and an amplifier 40 is provided to obtain a gain after frequency conversion. The current is increasing. Therefore, the mixer 35 needs to control the power supply by the burst power supply control signal.

However, the impedance of the local oscillation signal input end of the mixer 35 is often 50 Ω in the high frequency band due to the power supply, but it is guaranteed only when the power is constantly supplied. Currently, 50 Ω when the power supply is controlled by the burst power supply control signal
Consistency is only when power is applied. Therefore, the impedance changes at the rise and fall of the burst power control signal.

The voltage controlled oscillator 34 includes a mixer 35.
Depending on the input impedance of the local oscillation signal input end of
The characteristics of the tuning voltage that is the input and the frequency of the local oscillation signal that is the output change, for example, from the state shown by the solid line in FIG. 8 to the state shown by the alternate long and short dash line. Therefore, for example, the following phenomenon occurs. Now voltage controlled oscillator 3
It is assumed that the tuning voltage Vt is Vt0 when the frequency f of the local oscillation signal which is the output of No. 4 is locked at f0. In this state, when the input impedance of the local oscillation signal input terminal of the mixer 35 is changed by the power supply control by the burst power supply control signal, the characteristic of the voltage controlled oscillator 6 is instantaneously changed from the solid line state in FIG. 8 to the dashed line state. To do. The tuning voltage Vt at the moment of this change is Vt
Since it is considered that 0 is held, the frequency of the local oscillation signal, that is, the oscillation frequency f0 is f as shown by arrow A in FIG.
Shake for a moment to transition to 1. However, the frequency synthesizer circuit determines that the lock is released, and operates according to the characteristic indicated by the alternate long and short dash line in FIG. 8 so as to converge to f0 through the transition shown by arrow B in FIG. 8, resulting in the tuning voltage Vt. Settles on Vt1. That is, the tuning voltage Vt changes as shown in FIG.
The oscillation frequency f changes as shown in FIG. The convergence speed is determined by the loop characteristic of the frequency synthesizer circuit. Depending on the characteristic, the fluctuation of the frequency leads to the phase fluctuation at the rising portion of the RF modulation signal and deteriorates the modulation accuracy.

As described above, the conventional frequency synthesizer circuit has a problem that the phase of the RF modulation signal fluctuates due to ON / OFF of the power supply of the mixer 35, and the modulation accuracy deteriorates. The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a frequency synthesizer circuit that can prevent a phase variation of an RF modulation signal due to a disturbance and that has good modulation accuracy.

[0008]

According to the present invention, an offset voltage for canceling the fluctuation of the frequency due to the disturbance signal based on the disturbance signal which causes the fluctuation of the frequency of the local oscillation signal which is the output of the voltage controlled oscillator. Is provided, and an offset signal adding circuit that adds the offset voltage from the offset signal generating circuit to the tuning voltage and supplies the voltage to the voltage controlled oscillator.

[0009]

The offset signal generating circuit generates an offset voltage for canceling the fluctuation of the frequency due to the disturbance signal, based on the disturbance signal which causes the fluctuation of the frequency of the local oscillation signal output from the voltage controlled oscillator. The offset signal addition circuit adds the offset voltage from the offset signal generation circuit to the tuning voltage and supplies the tuning voltage to the voltage controlled oscillator.

[0010]

Embodiments of the present invention will now be described in detail with reference to the drawings. FIG. 1 is a circuit block diagram of a frequency synthesizer circuit according to an embodiment of the present invention. This frequency synthesizer circuit includes a reference oscillator 1, a phase comparator 2, a low pass filter 3, an offset signal generating circuit 4, Offset signal addition circuit 5, voltage controlled oscillator 6, mixer 7
And a comparison frequency divider 8. The reference oscillator 1 generates a frequency signal serving as a reference of the frequency switching width of the frequency synthesizer circuit and outputs it to the phase comparator 2. The phase comparator 2 detects a phase difference between the frequency signal from the reference oscillator 1 and the frequency-divided output signal from the comparison frequency divider 8 and supplies a voltage according to the phase difference to the low pass filter 3. The low pass filter 3 integrates the voltage from the phase comparator 2 and outputs it as a tuning voltage to the offset signal addition circuit 5. The offset signal generation circuit 4 generates an offset voltage based on the burst power supply control signal and outputs it to the offset signal addition circuit 5. The offset signal addition circuit 5
The offset voltage from the offset signal generation circuit 4 is added to the tuning voltage from the low pass filter 3 and the corrected voltage is output to the voltage controlled oscillator 6. The voltage controlled oscillator 6 generates a frequency signal according to the tuning voltage from the offset signal addition circuit 5, and outputs it as a local oscillation signal to the mixer 7 and the comparison frequency divider 8. The power supply of the mixer 7 is controlled by the burst power supply control signal, and based on the local oscillation signal from the voltage controlled oscillator 6 and the IF modulation signal, the mixer 7 outputs RF only during the burst period.
Output modulated signal. The comparison frequency divider 8 frequency-divides the local oscillation signal from the voltage controlled oscillator 6 according to the frequency division ratio data from the control unit (not shown), and outputs the frequency division output to the phase comparator 2.

FIG. 2 is a circuit diagram of the offset signal generating circuit 4. The offset signal generating circuit 4 is an operational amplifier OP.
1 and a variable resistor VR1. Operational amplifier O
The output terminal of P1 is connected to the inverting input terminal of the operational amplifier OP1 and the slider of the variable resistor VR1, and the non-inverting input terminal of the operational amplifier OP1 and one end of the variable resistor VR1 are grounded. The other end of the variable resistor VR1 is connected to the supply source of the burst power supply control signal.

FIG. 3 is a circuit diagram of the offset signal adder circuit 5. The offset signal adder circuit 5 is an operational amplifier OP.
2 and resistors R1 to R4. Operational amplifier O
The output terminal of P2 is connected to the non-inverting input terminal of the operational amplifier OP2 and one end of the resistor R2 via the resistor R1, and the inverting input terminal of the operational amplifier OP2 is connected to one end of the resistor R3 and one end of the resistor R4. It is connected to the. Resistor R2
Is connected to the output end of the offset signal generating circuit 4, and the other end of the resistor R3 is connected to the output end of the low pass filter 3. The other end of the resistor R4 is grounded.

Next, the operation will be described. When the burst power supply control signal as shown in FIG. 4A is input to the offset signal generation circuit 4, the offset signal generation circuit 4 inverts the burst power supply control signal and changes the level of the burst power supply control signal. The signal as shown in (b) is output to the offset signal addition circuit 5. That is, the variable resistor VR of FIG.
The level is adjusted by 1 and the polarity is inverted by the inverter configured by the operational amplifier OP1. The offset signal adding circuit 5 adds the signal from the offset signal generating circuit 4 and the signal from the low-pass filter 3 as shown in FIG. 4C, and outputs the signal as shown in FIG. 4D. The signal is output to the voltage controlled oscillator 6. That is, by the differential amplifier configured by the operational amplifier OP2 shown in FIG.
The signal from the offset signal generation circuit 4 and the signal from the low pass filter 3 are differentially amplified.

By the way, it is assumed that the frequency of the local oscillation signal output from the voltage controlled oscillator 6 is locked at f0 and the mixer 7 is not supplied with power.
When the mixer 7 is operated by the burst power supply control signal applied to the mixer 7 in this state, the input impedance of the local oscillation signal input end of the mixer 7 fluctuates, and the voltage controlled oscillator 6
Of the tuning voltage and the oscillation frequency of the voltage controlled oscillator 6 changes from the state shown by the solid line in FIG. 8 to the one-dot chain line as described above. The state changes to. Therefore, if the offset signal generation circuit 4 and the offset signal addition circuit 5 are not provided, frequency fluctuation occurs and the frequency converges to f0 through the transition shown by the arrow B in FIG.

At this time, the difference between the off period and the on period of the burst power supply control signal appears as the difference between Vt0 and Vt1 with respect to the tuning voltage Vt. Therefore, as in the present embodiment, the offset signal generation circuit 4 and the offset signal addition circuit 5 are provided so that the tuning voltage Vt0 is supplied to the tuning voltage input terminal of the voltage controlled oscillator 6 in the off period in synchronization with the burst power supply control signal. If the tuning voltage Vt1 is applied in advance during the ON period, the oscillation frequency f0 of the voltage controlled oscillator 6 does not change as shown in (e) of FIG. 7 even if the input impedance of the mixer 7 changes. Therefore, the phase of the RF modulation signal does not change even when the mixer 7 is powered on / off, and good modulation accuracy can be maintained.

[0016]

As described above, according to the present invention, on the basis of the disturbance signal which causes the frequency of the local oscillation signal which is the output of the voltage controlled oscillator, the frequency fluctuation due to the disturbance signal is canceled. Since an offset signal generating circuit for generating the offset voltage of (1) and an offset signal adding circuit for adding the offset voltage from the offset signal generating circuit to the tuning voltage and supplying it to the voltage controlled oscillator are provided, Phase fluctuations can be prevented, and good modulation accuracy can be maintained.

[Brief description of drawings]

FIG. 1 is a circuit block diagram of a frequency synthesizer circuit according to an embodiment of the present invention.

FIG. 2 is a circuit diagram of an offset signal generation circuit provided in a frequency synthesizer circuit according to an embodiment of the present invention.

FIG. 3 is a circuit diagram of an offset signal addition circuit provided in a frequency synthesizer circuit according to an embodiment of the present invention.

FIG. 4 is a signal waveform diagram of each part of the frequency synthesizer circuit in the embodiment of the present invention.

FIG. 5 is a circuit block diagram of a conventional frequency synthesizer circuit.

FIG. 6 is a circuit diagram of a mixer included in a conventional frequency synthesizer circuit.

FIG. 7 is a signal waveform diagram of each part of a conventional frequency synthesizer circuit.

FIG. 8 is an explanatory diagram of input / output characteristics of the voltage controlled oscillator.

[Explanation of symbols]

 4 Offset signal generation circuit 5 Offset signal addition circuit 6 Voltage controlled oscillator

Continuation of front page (51) Int.Cl. ⁶ Identification code Office reference number FI Technical display area H03L 7/093

Claims (1)

[Claims] 1. An offset signal generation circuit for generating an offset voltage for canceling the fluctuation of the frequency due to the disturbance signal, based on the disturbance signal which causes the frequency of the local oscillation signal output from the voltage controlled oscillator to fluctuate. And an offset signal adding circuit for adding an offset voltage from the offset signal generating circuit to a tuning voltage and supplying the voltage to the voltage-controlled oscillator, the frequency synthesizer circuit.