A single operational amplifier charge pump circuit for phase-locked loop

Abstract

The present invention discloses a single operational amplifier charge pump circuit for a phase-locked loop, the charge pump circuit comprising: a single operational amplifier; a first field effect tube; a second field effect tube; a first current source switch; a second current source switch; a first current sink switch; a second current sink switch; the single operational amplifier has two output terminals, the two output terminals are respectively connected to the gate of the first field effect tube and the gate of the second field effect tube, the source currents of the two field effect tubes are respectively a current source and a current sink, the first current source switch, the second current source switch, the first current sink switch and the second current sink switch are mutually connected to form a loop, and the non-inverting input terminal of the single operational amplifier is connected to the phase-locked loop. The charge pump circuit designs the branch that is not connected to the low-pass filter in a single operational amplifier into the entire amplifier circuit structure, which can simultaneously solve the voltage mutation problem and the upper and lower current mismatch problem caused by the charge sharing effect.

Description

Technical Field

[0001] The present invention relates to the technical field of charge pumps, and in particular to a single operational amplifier charge pump circuit for a phase-locked loop. Background Art

[0002] In the existing charge pump circuit, when the operational amplifier is used as a follower, the input voltage of the operational amplifier needs to be equal to the output voltage, so that when the branch output to the low-pass filter is opened, the sudden change of the input voltage caused by the charge sharing effect can be reduced. The existing charge pump circuit cannot solve the problem of sudden change of the input voltage of the operational amplifier caused by the current mismatch between the current sink and the current source in a single amplifier. Summary of the invention

[0003] One of the inventive purposes of the present invention is to provide a single operational amplifier charge pump circuit for a phase-locked loop. The charge pump circuit designs a branch that is not connected to a low-pass filter into the entire amplifier circuit structure in a single operational amplifier, which can simultaneously solve the voltage mutation problem and the upper and lower current mismatch problem caused by the charge sharing effect.

[0004] Another inventive object of the present invention is to provide a single operational amplifier charge pump circuit for a phase-locked loop, wherein the charge pump circuit is configured with two field effect transistors of different channel types on a circuit connected to a single amplifier, and the two field effect transistors can be connected to the single amplifier to form an amplifier with one more amplification stage, and the output end of the single amplifier is connected to the inverting input end to form a source-following structure, which can effectively solve the technical problem of power supply sharing.

[0005] Another object of the present invention is to provide a single operational amplifier charge pump circuit for a phase-locked loop, wherein the charge pump circuit achieves the current matching problem between the current source and the current sink through two field effect transistors. Due to the single amplifier structure, the cost of the charge pump circuit can be reduced.

[0006] In order to achieve at least one of the above-mentioned invention objects, the present invention further provides a single operational amplifier charge pump circuit for a phase-locked loop, the charge pump circuit comprising:

[0007] A single operational amplifier;

[0008] The first field effect transistor;

[0009] The second field effect transistor;

[0010] a first current source switch;

[0011] a second current source switch;

[0012] a first current sink switch;

[0013] a second current sink switch;

[0014] The single operational amplifier has two output terminals, which are respectively connected to the gate of the first field effect transistor and the gate of the second field effect transistor. The source currents of the two field effect transistors are current sources and current sinks respectively. The first current source switch, the second current source switch, the first current sink switch and the second current sink switch are interconnected to form a loop. The non-phase input terminal of the single operational amplifier is connected to a phase-locked loop.

[0015] According to one of the preferred embodiments of the present invention, the two field effect transistors include a pmos transistor and a nmos transistor, wherein the source of the pmos transistor is connected to a current source, and the source of the nmos transistor is connected to a current sink.

[0016] According to another preferred embodiment of the present invention, the operational amplifier includes a first output terminal and a second output terminal, wherein the gate of the pmos tube is connected to the first output terminal, and the nmos tube is connected to the second output terminal.

[0017] According to another preferred embodiment of the present invention, the non-inverting input terminal of the single operational amplifier is connected to a loop formed by the first current source switch, the second current source switch, the first current sink switch and the second current sink switch, and the non-inverting input terminal is connected between the first current source switch and the first current sink.

[0018] According to another preferred embodiment of the present invention, the inverting input terminal of the operational amplifier is connected to a loop formed by the first current source switch, the second current source switch, the first current sink switch and the second current sink switch, and the inverting input terminal is connected between the second current source switch and the second current sink switch.

[0019] According to another preferred embodiment of the present invention, a first inverter is installed in the circuit between the first current source switch and the second current source switch.

[0020] According to another preferred embodiment of the present invention, a second inverter is installed in the circuit between the second current source switch and the first current sink.

[0021] According to another preferred embodiment of the present invention, the source and the drain of the pmos tube are respectively connected to the line between the first current source switch and the second current source switch of the loop.

[0022] According to another preferred embodiment of the present invention, the source and drain of the nmos tube are respectively connected to the line between the second current source switch and the first current sink switch of the loop.

[0023] According to another preferred embodiment of the present invention, the non-inverting input terminal of the single operational amplifier is connected to a low-pass filter, the low-pass filter is grounded, and the inverting input terminal of the single operational amplifier is connected to one end of a capacitor, the other end of the capacitor is grounded. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 Shown is a structural schematic diagram of a single operational amplifier charge pump circuit for a phase-locked loop in one state of the present invention.

[0025] Figure 2 The figure shows a schematic diagram of another state of a single operational amplifier charge pump circuit in a phase-locked loop of the present invention, wherein UP is the first current source switch, / UP is the second current source switch, DN is the first current sink switch, / DN is the second current sink switch, P1 is the first field effect transistor, N1 is the second field effect transistor, vout1 is the first output terminal, vout2 is the second output terminal, isource is the current source current, isink is the current sink current, C1 is the first capacitor, and LPF is a low-pass filter. DETAILED DESCRIPTION

[0026] The following description is used to disclose the present invention so that those skilled in the art can implement the present invention. The preferred embodiments described below are only examples, and those skilled in the art can think of other obvious variations. The basic principles of the present invention defined in the following description can be applied to other embodiments, variations, improvements, equivalents, and other technical solutions that do not deviate from the spirit and scope of the present invention.

[0027] It is to be understood that the term "one" should be understood as "at least one" or "one or more", that is, in one embodiment, the number of an element may be one, while in another embodiment, the number of the element may be multiple, and the term "one" should not be understood as a limitation on the quantity.

[0028] Please combine Figure 1-Figure 2The present invention discloses a single operational amplifier charge pump circuit for a phase-locked loop, the charge pump circuit comprising a single operational amplifier, a first field effect transistor, a second field effect transistor, a first current source switch, a second current source switch, a first current sink switch, and a second current sink switch, wherein the first current source switch, the second current source switch, the first current sink switch, and the second current sink switch are interconnected to form a loop circuit, different positions on the loop are respectively connected to the first field effect transistor and the second field effect transistor and different pins of the operational amplifier, a first inverter is provided between the first current source switch and the second current source switch, and a second inverter is provided between the first current sink and the second current sink, the input end of the single operational amplifier is respectively connected to a low-pass filter and a phase-locked loop, the above four switches and inverters are arranged to enable the single operational amplifier to solve the problem of upper and lower current mismatch, and the single operational amplifier is used as a follower to reduce the problem of current mutation.

[0029] Specifically, the non-inverting input terminal of the single operational amplifier is connected to the above loop, and the non-inverting input terminal is connected between the first current source switch and the first current sink switch in the loop, the inverting input terminal of the single operational amplifier is connected to the loop, and the inverting input terminal is connected to the line between the second current source switch and the second current sink switch, which is used to invert the dead zone prevention pulse level from the phase-locked loop, the first field effect tube is a pmos tube, the source of the first field effect tube is connected to the line of the first current source switch and the second current source switch, and is close to the first current source. The drain of the first field effect tube is connected to the above loop, specifically connected to the line of the first current source switch and the second current source switch. The gate of the first field effect tube is connected to the first output terminal of the single operational amplifier, and the source of the first field effect tube is also connected to the current source. The second field effect transistor is an NMOS tube, the gate of the second field effect tube is connected to the second output end of the single operational amplifier, the source and drain of the second field effect tube are respectively connected to the loop, wherein the source of the second field effect tube is connected to the line of the first current sink switch and the second current sink switch, the drain of the second field effect tube is connected to the line of the first current sink switch and the second current sink switch, and the source of the second field effect tube is grounded.

[0030] The inverting output terminal is further connected to one end of a capacitor after being connected to the second current source switch and the second current sink switch of the loop, and one end of the capacitor is grounded.

[0031] In order to better illustrate the technical effect of the present invention, the present invention further explains the following two working states of the circuit:

[0032] Please refer to Figure 1The present invention shows a schematic diagram of a single operational amplifier charge pump circuit for a phase-locked loop when the phase-locked loop is in a locked state and the periodic pulses of the anti-dead zone output by the PFD (phase frequency detector) have not reached the charge pump. In this state, the first current source switch and the first current sink switch are in an open disconnected state of 0, that is, UP=DN='0', wherein the first current source switch, the second current source switch, the first current sink and the first current sink switch can be set as single-phase switches, and after being inverted by the first inverter, the second current source switch and the second current sink switch are in a closed conductive state of 1, that is, / UP= / DN='1', and the first output end of the single operational amplifier inputs the output current to the gate of the first field effect tube, and the drain of the first field effect tube is connected to the inverting input end of the single operational amplifier due to the closure and conduction of the first current source switch, so that the single operational amplifier and the first field effect tube form a common source amplifier with a first-level pmos input. Similarly, a common source amplifier with NMOS input is formed between the second output terminal of the single operational amplifier and the second field effect transistor, and an amplifier with an additional stage of amplification is formed between the first field effect transistor, the second field effect transistor and the single operational amplifier. Since the output of the single operational amplifier is fed back to the inverting input terminal to form a source-following structure, the voltage at the non-inverting input terminal of the single operational amplifier is equal to the voltage at the inverting input terminal, that is, vfb=vctrl, and the sum of the current of the current source and the current of the first field effect transistor is equal to the sum of the current sink current and the current of the second field effect transistor. The capacitor C1 can achieve the technical effect of stabilizing compensation for the amplifier, and can also protect the voltage connected to the non-inverting input terminal.

[0033] Please refer to Figure 2The present invention shows a circuit state diagram of a single operational amplifier charge pump circuit for a phase-locked loop when the phase-locked loop is in a locked state and the periodic pulse of the anti-dead zone output by the PFD (phase frequency detector) reaches the charge pump. In this circuit state, the first current source switch and the first current sink switch are in a closed conduction state of 1, that is, UP = DN = '1'. Due to the action of the first inverter and the second inverter, the second current source switch and the second current sink switch are in an open circuit state of 0, that is, / UP = / DN = '0'. Before the periodic pulse reaches the charge pump, the voltages of the positive input terminal and the negative input terminal of the single operational amplifier are equal to vfb = vctrl, and the voltage of the negative input terminal of the single operational amplifier is equal to the current source voltage and the current sink voltage, that is, vtop = vbot = vfb. When the first current source switch and the first current sink switch are closed and the second current source switch and the second current sink switch are open and disconnected, the voltage of the positive input terminal of the single operational amplifier is equal to the current source voltage and the current sink voltage, that is, vtop = vbot = vctrl. Thus, the sudden change of the voltage at the non-inverting input terminal of the single operational amplifier caused by the charge sharing effect can be eliminated to a large extent.

[0034] It is worth mentioning that when the branch of the inverting input terminal is in the closed conductive state of 1, the current source and the current sink are equal as the upper and lower currents, and in this state, the drain voltage of the first field effect tube is equal to the current source voltage and the inverting input terminal voltage, that is, the drain voltage of the first field effect tube = vtop = vfb = vctrl, and the drain voltage of the second field effect tube is equal to the current source voltage and the inverting input terminal voltage, that is, the drain voltage of the second field effect tube = vbot = vfb = vctrl. Since the inverting input terminal voltage of the single operational amplifier is equal to the positive input terminal voltage, that is, vfb = vctrl. When the periodic pulse reaches the charge pump, the second current source switch and the second current sink switch are disconnected, the first current source switch and the first current sink switch are closed and turned on, the drain voltage of the first field effect tube is equal to the positive input terminal of the single operational amplifier, that is, vtop = vctrl, and the drain voltage of the second field effect tube is equal to the positive input terminal of the single operational amplifier, that is, vbot = vctrl. The voltages of the non-inverting input and the inverting input of the single operational amplifier remain unchanged, that is, the voltages of the source, drain, and gate of the first field effect tube are the same as before, so during the circuit state switching, the sum of the current source current and the current of the first field effect tube is still equal to the sum of the current sink current and the current of the second field effect tube. This solves the problem of upper and lower current matching of the single operational amplifier. In the present invention, the above-mentioned loop structure prevents the charge from being released during the circuit state switching process, thereby preventing a sudden change in the voltage of the non-inverting input of the single operational amplifier.

[0035] Those skilled in the art should understand that the embodiments of the present invention described above and shown in the accompanying drawings are only examples and do not limit the present invention. The objectives of the present invention have been fully and effectively achieved. The functional and structural principles of the present invention have been demonstrated and explained in the embodiments. Without departing from the principles, the implementation methods of the present invention may be deformed or modified in any way.

Claims

1. A single operational amplifier charge pump circuit for a phase-locked loop, characterized in that: The charge pump circuit comprises: Single operational amplifier; The first field effect transistor; The second field effect transistor; a first current source switch; a second current source switch; a first current sink switch; a second current sink switch; The single operational amplifier has two output terminals, which are respectively connected to the gate of the first field effect transistor and the gate of the second field effect transistor. The source currents of the two field effect transistors are current sources and current sinks respectively. The first current source switch, the second current source switch, the first current sink switch and the second current sink switch are interconnected to form a loop. The non-phase input terminal of the single operational amplifier is connected to a phase-locked loop.

2. A single operational amplifier charge pump circuit for a phase-locked loop according to claim 1, characterized in that: The two field effect transistors include a pmos transistor and a nmos transistor, wherein the source of the pmos transistor is connected to a current source, and the source of the nmos transistor is connected to a current sink.

3. A single operational amplifier charge pump circuit for a phase-locked loop according to claim 2, characterized in that: The single operational amplifier comprises a first output terminal and a second output terminal, wherein the gate of the pmos tube is connected to the first output terminal, and the nmos tube is connected to the second output terminal.

4. A single operational amplifier charge pump circuit for a phase-locked loop according to claim 1, characterized in that: The non-inverting input terminal of the single operational amplifier is connected to a loop formed by the first current source switch, the second current source switch, the first current sink switch and the second current sink switch, and the non-inverting input terminal is connected between the first current source switch and the first current sink.

5. A single operational amplifier charge pump circuit for a phase-locked loop according to claim 1, characterized in that: The inverting input terminal of the single operational amplifier is connected to a loop formed by the first current source switch, the second current source switch, the first current sink switch and the second current sink switch and the inverting input terminal is connected between the second current source switch and the second current sink switch.

6. A single operational amplifier charge pump circuit for a phase-locked loop according to claim 1, characterized in that: A first inverter is installed in the circuit between the first current source switch and the second current source switch.

7. A single operational amplifier charge pump circuit for a phase-locked loop according to claim 1, characterized in that: A second inverter is installed in the circuit between the first current sink switch and the second current sink.

8. A single operational amplifier charge pump circuit for a phase-locked loop according to claim 2, characterized in that: The source and drain of the pmos tube are respectively connected to the line between the first current source switch and the second current source switch of the loop.

9. A single operational amplifier charge pump circuit for a phase-locked loop according to claim 2, characterized in that: The source and drain of the NMOS tube are respectively connected to the line between the first current sink switch and the second current sink switch of the loop.

10. The single operational amplifier charge pump circuit for a phase-locked loop according to claim 1, characterized in that: The non-inverting input terminal of the single operational amplifier is connected to a low-pass filter, which is grounded; and the inverting input terminal of the single operational amplifier is connected to one end of a capacitor, which is grounded.

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