JP3819509B2 - Constant current charge pump circuit for phase-locked loop - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a constant current type charge pump circuit used in a phase locked loop (PLL) suitable as a frequency synthesizer or the like.
[0002]
[Prior art]
The phase synchronization circuit is a circuit that obtains a local oscillation frequency with good frequency stability from a reference frequency. For example, as shown in FIG. 2, a phase comparator 101, a charge pump 110, a loop filter (LPF) 103, and a voltage controlled oscillator ( (VCO) 104 constitutes a closed loop. The output frequency of the voltage controlled oscillator 104 and its phase are compared with the reference frequency and its phase input from the input terminal IN by the phase comparator 101, and a phase error is detected. The phase error component is input to the charge pump 110 as a frequency DOWN (charge-down) signal or a frequency UP (charge-up) signal, and the charge pump 110 draws in or flows out current in response to the DOWN or UP signal. This current is converted to a voltage by the loop filter 103, and after unnecessary waves and noise are reduced, the current is input to the voltage controlled oscillator 104 to control the frequency and phase of the voltage controlled oscillator 104. The output of the voltage controlled oscillator 104 is input to the phase comparator 101 again. This series of loops is repeated, and the output frequency and phase of the voltage controlled oscillator 104 are synchronized with the reference frequency and phase.
[0003]
FIG. 4 shows a conventional constant current type charge pump circuit 110 used in a phase locked loop circuit having such a function. In the circuit of FIG. 4, when the DOWN signal is input High from the phase comparator 101, the transistor Q24 is turned on. At this time, since the UP signal is low, the transistor Q21 is turned off. As a result, the transistors Q22 and Q23 are turned off, and no current flows from the constant voltage power supply Vcc to the transistor Q23. A current flows from the loop filter 103 to the transistor Q24 and the resistor R26 through the control input / output terminal Vin-out. The current at this time is determined by the voltage value obtained by dividing the voltage Vdown of the DOWN signal by resistors R24 and R25 = {R25 / (R24 + R25)} × Vdown. Since the transistor Q21 is turned on when the UP signal is high, the transistors Q22 and Q23 are turned on, and since the DOWN signal is low, the transistor Q24 is turned off, and the current from the constant voltage power supply Vcc is the transistor It flows through Q23 and flows out to the loop filter 103 via the control input / output terminal Vin-out. The current at this time is determined by the voltage value obtained by dividing the voltage Vup of the UP signal by resistors R21 and R22 = {R22 / (R21 + R22)} × Vup.
[0004]
[Problems to be solved by the invention]
In the configuration of the conventional constant current type charge pump circuit 110 described above, the current from the loop filter 103 when the DOWN signal is input from the phase comparator 101 or the current to the loop filter 103 when the UP signal is input, It is determined only by the value obtained by dividing the voltage of the DOWN signal or the voltage of the UP signal by resistors R24 and R25 or resistors R21 and R22, respectively. That is, there are two independent current paths, a current path composed of resistors R24 and R25, and a current path composed of resistors R21 and R25. Therefore, if the resistance values of ICs (integrated circuits) constituting the circuit vary, the current value cannot be determined. When designing the loop filter 103 that actually configures the phase-locked loop circuit, the constant current value of the control input / output terminal Vin-out of the charge pump circuit 110 cannot be defined. There was an obstacle that was difficult to do.
[0005]
The present invention has been made to solve such a problem, and provides a constant current type charge pump circuit that is less affected by variations in the performance of ICs and variations in resistance values. The object is to realize circuit operation in a stable state of the phase synchronization circuit.
[0006]
[Means for Solving the Problems]
A constant current type charge pump circuit for a phase locked loop circuit of the present invention made to achieve the above object will be described with reference to FIGS. 1 and 2 corresponding to the embodiments.
[0007]
The constant current type charge pump circuit for phase locked loop circuit to which the present invention is applied is used for the phase locked loop circuit shown in FIG. In this phase synchronization circuit, the phase comparator 101, the charge pump 102, the loop filter 103, and the voltage controlled oscillator 104 constitute a closed loop, and a current flows from the loop filter 103 by the charge-down signal from the phase comparator 101, and the charge-up signal As a result, current flows out to the loop filter 103. As shown in FIG. 1, the constant current type charge pump circuit 102 constitutes a single constant current source circuit that always conducts current from the constant voltage power source Vcc with the transistor Q3 that divides the resistors R1 and R4. This transistor Q3 has two transistors Q4 and Q15 which are current mirror circuits, one of which is a charge-down signal as an operation signal and the other current mirror circuit is an operation signal as a charge-up signal. It is characterized by that.
[0008]
Further, in the constant current type charge pump circuit for phase locked loop circuit according to the present invention, the current mirror circuit of the charge-down signal is connected to the pair of transistors Q1 and Q2 which are respectively switched by the differential between the positive signal and the inverted signal of the charge-down signal. connect, you are connected to the transistor Q14 and Q17 of the pair of operating each switch by the differential between the positive signal and the inverted signal of the current mirror circuit is a charge-up signal of the charge-up signal.
[0009]
This constant current type charge pump circuit can be appropriately implemented by being constituted by an integrated circuit.
[0010]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings.
[0011]
A configuration of an embodiment of a constant current type charge pump circuit for a phase locked loop circuit to which the present invention is applied is shown in FIG. The charge pump circuit 102 constitutes a closed loop of a phase locked loop circuit together with, for example, the phase comparator 101, the charge pump 102, the loop filter (LPF) 103, and the voltage controlled oscillator (VCO) 104 shown in FIG.
[0012]
In the charge pump circuit 102 of FIG. 1, DOWN is an input signal from the phase comparator 101, -DOWN is an input signal obtained by inverting the input signal, and DOWN and -DOWN have a differential signal relationship. Similarly, UP is an input signal from the phase comparator 101, -UP is an input signal obtained by inverting the input signal UP, and UP and -UP have a differential signal relationship. Vcc is a constant voltage power supply for circuit operation, and Vin-out is a control input / output terminal for inputting / outputting a control current between the loop filter 103 and the charge pump circuit 102. Q10, Q11, Q18, Q19 are PNP transistors, Q1, Q2, Q3, Q4, Q8, Q14, Q15, Q16, Q17 are NPN transistors, R1, R2, R3, R4, R5, R6, R11, R12, R13 , R14 is a resistor.
[0013]
In this circuit, the base of the transistor Q3 is steadily turned on because a voltage is applied from the power supply Vcc, and the resistor R1, the transistor Q3, and the resistor R4 are constant constant current sources. The transistor Q3 and the transistor Q4 are paired to constitute a current mirror, the transistor Q4 is steadily turned on, and the transistor Q3 and the transistor Q15 are paired to constitute a current mirror, and the transistor Q15 is stationary. Turned on.
[0014]
When pulses of the input signals DOWN and -DOWN are input from the phase comparator 101, they operate as differential signals, the transistor Q1 is turned on, the transistor Q2 is turned off, and the base potential is lowered together with the collector potential of the transistor Q10. Current flows. A current also flows through transistor Q10 and transistor Q11 which is a current mirror, and further a current flows through resistor R3, transistor Q8 and resistor R6. Transistor Q8 and transistor Q16, which is a current mirror, are also turned on. However, since the pulse of the input signal DOWN is turned on, the input signal UP is off and the transistor Q14 is off. And the base potential remains off without lowering. Therefore, a current flows from the loop filter 103 to the transistor Q16 through the control input / output terminal Vin-out.
[0015]
When a pulse of the input signal UP and -UP is input from the phase comparator 101, it operates as a differential signal. Since the transistor Q14 is turned on and the transistor Q17 is turned off, a current flows through the resistor R11 and the transistor Q18. A current flows through the transistor Q19 of the mirror. When the pulse of the input signal UP is on, the input signal DOWN is off. Therefore, the transistor Q16 is off, and the current from the power source Vcc flowing through the resistor R12 and the transistor Q19 is It flows into the loop filter 103 via the control input / output terminal Vin-out.
[0016]
In the above circuit operation, the constant current from the constant voltage power source Vcc flows through the resistor R1, the transistor Q3, and the resistor R4, and the current value is determined by the values of the resistor R1 and the resistor R4. From the constant voltage power supply Vcc (for example, Vcc = 3V), the base potential of the transistor Q3 depends on the voltage drop of the resistor R1, the voltage drop between the base and emitter of the transistor Q3 (about 0.8V), and the voltage drop of the resistor R4. decide. The values of the resistors R1 and R4 can be arbitrarily selected, the current value is determined by the resistance value, and the base potential of the transistor Q3 can be selected (for example, around 1V). Since the transistor Q3 and the transistor Q4 constitute a pair constituting a current mirror, and the transistor Q3 and the transistor Q15 constitute a pair constituting a current mirror, the constant current determined by the values of the resistors R1 and R4 as described above is the resistor R5. And flows to the resistor R13. As a result, whether the input signal is DOWN or UP, the current value of the control input / output terminal Vin-out is determined by the values of the resistors R1 and R4.
[0017]
Further, as in the charge pump circuit 102 of this embodiment, by making the connection with the phase comparator 101 differential (a connection between DOWN and -DOWN and a connection between UP and -UP), it is caused by disturbance such as noise. Another advantage is that it is less affected.
[0018]
FIG. 3 shows characteristics when the operation of the phase locked loop circuit of FIG. 2 using the charge pump circuit 102 of FIG. 1 is simulated. (A) is the voltage at the control input / output terminal Vin-out of the charge pump circuit 102 when the DOWN signal is input from the phase comparator 101, and the output voltage from the loop filter 103 to the voltage controlled oscillator 104. (B) is the voltage at the control input / output terminal Vin-out of the charge pump circuit 102 when the UP signal is input from the phase comparator 101, and the output voltage from the loop filter 103 to the voltage controlled oscillator 104. (A) When the signal is DOWN, the change in the voltage of the control input / output terminal Vin-out per time is V / t = 6285 (V / sec), and (b) When the signal is UP, the control input / output terminal Vin-out The change per hour in the voltage of V / t = 6278 (V / sec) is almost the same, and the effect that both voltages are obtained from a single constant current source appears. ing. In the case of (a) the DOWN signal and (b) the UP signal, the output voltage of the loop filter 103 is delayed from the voltage of the control input / output terminal Vin-out of the charge pump 102. This is because of the time constant.
[0019]
【The invention's effect】
As described above in detail, the constant current type charge pump circuit for the phase locked loop circuit to which the present invention is applied determines the input / output current to the loop filter constituting the phase locked loop with a single constant current source. Even if there are variations in the constants of parts on the circuit, the circuit configuration is less susceptible to the influence. In the conventional constant current type charge pump circuit, the current value from the loop filter when the DOWN signal is input and the current value to the loop filter when the UP signal is input are constants of the components constituting the circuit. If there were variations, they did not match. However, the circuit of the present invention has an advantage that the current value from the loop filter matches the current value to the loop filter even in such a case.
[Brief description of the drawings]
FIG. 1 is a diagram showing an embodiment of a constant current type charge pump circuit for a phase locked loop circuit to which the present invention is applied.
FIG. 2 is a block diagram illustrating an example of a phase synchronization circuit.
FIG. 3 is a diagram showing characteristics of a phase locked loop circuit using the charge pump circuit of the present invention.
FIG. 4 is a diagram showing an example of a conventional constant current type charge pump circuit.
[Explanation of symbols]
101 is a phase comparator, 102 is a charge pump, 103 is a loop filter (LPF), 104 is a voltage controlled oscillator (VCO), Q10, Q11, Q18, Q19, Q22, Q23 are PNP transistors, Q1, Q2, Q3, Q4 , Q8, Q14, Q15, Q16, Q17, Q21, Q24 are NPN transistors, R1, R2, R3, R4, R5, R6, R11, R12, R13, R14, R21, R22, R23, R24, R25, R26 are Resistance, UP, -UP, DOWN, -DOWN are input terminals, Vin-out is a control input / output terminal, Vcc is a constant voltage power input terminal.

Claims (2)

Used in a phase-locked loop configured with a phase comparator, charge pump, loop filter, and voltage-controlled oscillator. Current flows from the loop filter with the charge-down signal from the phase comparator, and into the loop filter with the charge-up signal. In a constant current type charge pump circuit in which current flows out, a transistor that divides a resistor constitutes a single constant current source circuit that always conducts current from a constant voltage power supply, and this transistor serves as two current mirror circuits One of the current mirror circuits is connected to a pair of transistors that perform switching operation by the differential between the positive and inverted signals of the charge-down signal and used as an operation signal, and the other current mirror circuit is charged up. each switch operates according to a differential between the positive signal and the inverted signal of the signal Constant current charge pump circuit, characterized in that the operation signals are connected to a transistor pair that.     The constant current type charge pump circuit according to claim 1, wherein the constant current type charge pump circuit is constituted by an integrated circuit.

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