Charge pump with temperature compensation and phase-locked loop

Abstract

The invention discloses a charge pump with temperature compensation and a phase-locked loop, the charge pump comprises a constant current source, a temperature control current source, a proportion module and a control module, the proportion module is used for combining the constant current source and the temperature control current source according to a certain proportion and outputting combined current to a control unit; when the charge pump forwards injects current into the next-stage circuit, the control module injects current formed by combining the constant current source and the temperature control current source according to a certain proportion into the next-stage circuit; and when the charge pump reversely extracts the current from the next stage, the control module extracts the current formed by combining the constant current source and the temperature control current source according to a certain proportion from the next stage of circuit. According to the scheme, the PTAT current and the constant current are combined according to a certain proportion to generate the power supply voltage of the KVCO for compensation, so that temperature compensation is realized, and meanwhile, the problem of excessive compensation is avoided.

Description

Technical Field

[0001] The present invention relates to the field of semiconductor technology, and particularly to a charge pump with temperature compensation and a phase-locked loop (PLL). Background Art

[0002] One of the key indicators of a phase-locked loop (PLL) circuit is the loop bandwidth, which depends on the charge pump current, the loop filter resistance, and the gain (K vco ) of the voltage-controlled oscillator (VCO). The gain of the VCO depends on PVT (Process-Voltage-Temperature), and temperature is an important factor among them. When the chip operating temperature changes, it will cause the loop bandwidth to change, thereby reducing the chip performance.

[0003] In the prior art, either no temperature-related compensation is performed, or pure PTAT current is used for compensation, but this solution is prone to over-compensation problems. Summary of the Invention

[0004] To solve this problem, the present invention patent reduces the influence of the PLL circuit bandwidth on temperature by introducing a method of temperature compensation with adjustable ratio at the charge pump, thereby improving the chip performance.

[0005] The present invention provides a charge pump with temperature compensation, comprising:

[0006] A constant current source, a temperature-controlled current source, a ratio module, and a control module, wherein the ratio module is used to combine the constant current source and the temperature-controlled current source in a certain ratio and output the combined current to the control unit;

[0007] When the charge pump injects current forward into the subsequent stage circuit, the control module injects the current combined by the constant current source and the temperature-controlled current source in a certain ratio into the subsequent stage circuit;

[0008] When the charge pump extracts current reversely from the subsequent stage, the control module extracts the current combined by the constant current source and the temperature-controlled current source in a certain ratio from the subsequent stage circuit.

[0009] The present invention further provides a phase-locked loop with temperature compensation, comprising:

[0010] A voltage-controlled oscillator, a low-pass filter, a charge pump, and a frequency discriminator / phase discriminator;

[0011] The charge pump includes a constant current source, a temperature-controlled current source, a control module, and a ratio module, wherein the ratio module is used to combine the constant current source and the temperature-controlled current source in a certain ratio and output the combined current to the control unit;

[0012] When the charge pump outputs forward to the low-pass filter, the control module inputs the current after combining a constant current source and a temperature-controlled current source to the low-pass filter according to a certain ratio;

[0013] When the charge pump reversely returns current from the low-pass filter, the control module extracts the current after combining a constant current source and a temperature-controlled current source to the low-pass filter according to a certain ratio.

[0014] Compared with the existing scheme, the advantages of the present invention are as follows:

[0015] In this scheme, by combining the PTAT current and the constant current according to a certain ratio, the control voltage of the KVCO is generated to compensate the loop bandwidth, so as to achieve temperature compensation and avoid the problem of over-compensation at the same time. Brief Description of the Drawings

[0016] By describing the exemplary embodiments of the present invention in more detail in conjunction with the drawings, the above and other objects, features and advantages of the present invention will become more obvious. Among them, in the exemplary embodiments of the present invention, the same reference numerals generally represent the same components.

[0017] Figure 1 It is a schematic structural diagram of a phase-locked loop with temperature compensation according to the present invention;

[0018] Figure 2 It is a schematic diagram of a charge pump with temperature compensation according to an embodiment of the invention;

[0019] Figure 3 It is a circuit diagram of a charge pump with temperature compensation according to an embodiment of the invention;

[0020] Figure 4 It is a circuit diagram of a proportional module of a charge pump with temperature compensation according to an embodiment of the invention;

[0021] Figure 5 It is a circuit diagram of a current source of a charge pump with temperature compensation according to an embodiment of the invention. Detailed Description of the Invention

[0022] A typical phase-locked loop circuit is as Figure 1 shown, and is composed of a voltage-controlled oscillator (VCO), a low-pass filter (LPF), a charge pump (CP), a frequency divider (DIV) and a phase frequency detector (PFD).

[0023] The bandwidth of the phase-locked loop is one of the key indicators of the phase-locked loop. The loop bandwidth affects the loop stability and system performance of the phase-locked loop. Its loop bandwidth is:

[0024] Where I cp is the current at the charge pump, R lf is the resistance of the loop filter, Kvco is the gain of the oscillator. All parameters are affected by process corners and temperature, leading to large process corner and temperature fluctuations in the PLL loop bandwidth. In traditional designs, I cp is typically generated by a bandgap reference voltage (V bgr ) and a poly resistor (R poly ) on the chip, resulting in a current (i.e., I pp ). I cp = V bgr / R poly . The loop filter resistor R lf is also usually a poly resistor on the chip. Then, there will be I cp * R lf = V bgr * R lf / R poly . Since the bandgap reference voltage (V bgr ) is little affected by temperature and process, if R lf / R poly is well-matched, then I cp * R lf = I pp * R lf will hardly be affected by temperature and process. However, K vco is relatively complex and varies with temperature, process, and control voltage. As the temperature rises, K vco becomes smaller. Usually, when the chip is powered on, calibration is performed, during which the process deviation can be calibrated out, i.e., K vco is calibrated out along with the process deviation. However, during the normal operation of the chip after calibration, the temperature may change, leading to a change in K vco . For a ring oscillator, as the temperature rises, K vco decreases, resulting in a smaller loop bandwidth.

[0025] The preferred embodiments of the present invention will be described in more detail below. Although the preferred embodiments of the present invention are described below, it should be understood that the present invention can be implemented in various forms and should not be limited by the embodiments set forth herein.

[0026] Refer to Figure 1 and Figure 2, the present invention provides a charge pump with temperature compensation, which includes a constant current source, a temperature-controlled current source, a proportionality module, and a control module. The proportionality module is used to combine the constant current source and the temperature-controlled current source in a certain proportion and output the combined current to the control unit. When the charge pump outputs current forward to the subsequent circuit, the control module outputs the current combined by the constant current source and the temperature-controlled current source in a certain proportion. When the charge pump draws current back from the subsequent circuit, the control module inputs the current combined by the constant current source and the temperature-controlled current source in a certain proportion from the subsequent circuit.

[0027] In one embodiment, as Figure 3 shown, the control module includes a first current mirror 110 connected to the negative power supply (GND in this embodiment) and a second current mirror 120 connected to the high level. The reference current input terminal of the first current mirror 110 is connected to the current output terminal of the combined constant current source and temperature-controlled current source. In this embodiment, it is connected to the output terminal of the proportionality module. The first current output terminal of the first current mirror 110 is connected to the reference current input terminal of the second current mirror 120, and the second current output terminal of the first current mirror 110 is connected to the current output terminal of the second current mirror 120 through the control module.

[0028] Continue to refer to Figure 3 , in one embodiment, the control module further includes a first forward switch S1 and a first reverse switch S2 connected in series between the current output terminal of the second current mirror 120 and the second current output terminal of the first current mirror 110. The connection point of the first forward switch S1 and the first reverse switch S2 is connected to the subsequent low-pass filter LPD.

[0029] Continue to refer to Figure 3 , in one embodiment, the control module further includes a second forward switch S3, a second reverse switch S4, and an operational amplifier 130. The second forward switch S3 and the second reverse switch S4 are connected in series between the second current output terminal of the first current mirror 110 and the current output terminal of the second current mirror 120. The positive input terminal of the operational amplifier 130 is connected to the connection point of the first forward switch S1 and the first reverse switch S2, and the negative input terminal and the output terminal of the operational amplifier are connected to the connection point of the second forward switch S3 and the second reverse switch S4.

[0030] Specifically, in one embodiment, the first current mirror 110 includes a first NMOS transistor N1, a second NMOS transistor N2, and a third NMOS transistor N3. The sources of the first NMOS transistor N1, the second NMOS transistor N2, and the third NMOS transistor N3 are grounded, and their gates are connected and connected to the drain of the first NMOS transistor N1. The drain of the first NMOS transistor N1 is the reference current input terminal of the first current mirror. The drain of the second NMOS transistor N2 is the first current output terminal, and the drain of the third NMOS transistor N3 is another first current output terminal.

[0031] The second current mirror 120 includes a first PMOS transistor P1 and a second PMOS transistor P2. The sources of the first PMOS transistor P1 and the second PMOS transistor P2 are connected to the positive power supply voltage, and their gates are connected to the drain of the first PMOS transistor P1. The drain of the first PMOS transistor P1 is the reference current input terminal of the second current mirror, and the drain of the second PMOS transistor P2 is the second current output terminal.

[0032] In one embodiment, refer to Figure 4 , the temperature-controlled current source is a PTAT current source. The proportional circuit includes: a third current mirror 210, which is used to provide the mirror current of the PTAT current source; a first current mirror group 220 connected in parallel, which is used to provide the proportional current of the PTAT current; a fourth current mirror 230, which is used to provide the mirror current of the constant current source; a second current mirror group 240 connected in parallel, which is used to provide the proportional current of the constant current. The outputs of the first current mirror group and the second current mirror group are connected to output the current after the constant current source and the temperature-controlled current source are combined in a certain proportion.

[0033] In this embodiment, the proportional circuit further includes a gating circuit, which dynamically adjusts the combined current by selecting the number of current mirrors in the first current mirror group and the second current mirror group.

[0034] In this embodiment, it further includes: the gating circuit is encoded according to three-bit binary, and one encoding corresponds to a proportional selection relationship between a fixed current source and a temperature-controlled current source.

[0035] Specifically, the first current mirror group 220 includes PMOS transistors P9, P10, P11, and P12. Among them, the gate and drain of the PMOS transistor P9 are connected to the current output terminal of the third current mirror 210, and the source is connected to the power supply line. The gates of the PMOS transistors P10, P11, and P12 are connected to the gate of the PMOS transistor P9, and the drains are connected to the output terminal to output a proportional temperature-controlled current. The sources of the PMOS transistors P10, P11, and P12 are respectively connected to the power supply line through their gating circuits. As Figure 4The gating of the PMOS transistor P10 shown is achieved by using the PMOS transistor P15, whose gate is the gating control terminal and is controlled by the digitally encoded Ictrl[2] bit. The PMOS transistors P11 and P12 are sequentially controlled by the digitally encoded Ictrl[1] and Ictrl[0] bits respectively.

[0036] The second current mirror group 240 includes PMOS transistors P20, P21, P23, P24, and P25. Among them, the gate and drain of the PMOS transistor P20 are connected to the current output terminal of the fourth current mirror 230, and the source is connected to the power supply line. The gates of the PMOS transistors P21, P23, P24, and P25 are connected to the gate of the PMOS transistor P20, the drains are connected to the output terminal and are connected to the output of the first current mirror group, and the second current mirror outputs a constant current in a certain proportion. The sources of the PMOS transistors P21, P23, and P24 are respectively connected to the power supply line through their gating circuits. As Figure 4 The gating of the PMOS transistor P21 shown is achieved by using the PMOS transistor P26, whose gate is the gating control terminal and is controlled by the digitally encoded Ictrl[2] bit. The PMOS transistors P27 and P28 are sequentially controlled by the digitally encoded Ictrl[1] and Ictrl[0] bits respectively. The source of the PMOS transistor P25 is connected to the power supply line through the PMOS transistor P29 whose gate is connected to the negative power supply.

[0037] In other embodiments, the current mirror group may include a different number of current mirrors to achieve an output current more suitable for the application.

[0038] In the present invention, the constant current source is mainly a current source generated by a bandgap reference voltage and a poly resistor in the chip. The temperature-controlled current source utilizes a PTAT (Proportional To Absolute Temperature) current source. The PTAT current generated by the PTAT current source is a current proportional to the absolute temperature. The PTAT current is generated through a specific circuit structure, usually including the temperature-dependent characteristics of diodes or transistors. The magnitude of the PTAT current increases linearly with the increase in temperature. This is because the voltage drop of the diode or transistor (such as the base-emitter voltage) decreases with the increase in temperature, resulting in an increase in current. It includes two transistors of different sizes, and by controlling their current density ratio, a current proportional to the temperature is generated.

[0039] In one embodiment, the temperature-controlled current source and the constant current source, such as Figure 5As shown, in this embodiment, there is a PTAT current source and a Poly current source circuit. These circuits are used to generate a temperature-compensated reference current within the chip. Among them, the output current of the PTAT current source is proportional to the absolute temperature. This current source utilizes the base-emitter voltage difference between BJTs (bipolar junction transistors) to generate the PTAT current. Bipolar transistors T1 and T2 operate at different current densities. Due to their different emitter currents, different base-emitter voltages (V BE ) are generated. Resistors R1 and R2 are respectively connected to the emitters of T1 and T2 and are used to determine the current ratio. Resistor R3 is used to stabilize the current. Operational amplifier A1 is used to maintain the base-emitter voltage difference between bipolar transistors T1 and T2 to ensure the generation of current Iptat. This circuit utilizes the temperature characteristic of (VBE_T1 - VBE_T2) to generate a current Iptat that is proportional to the temperature.

[0040] The Poly current source circuit is used to generate the poly current, which is usually process-related. Since the Bandgap voltage is used as the input of amplifier A2, this current source can maintain a relatively stable output when the temperature changes. PMOS transistors P31 and P32 are used to control the PTAT current Iptat. Operational amplifier A2, P33, and R4 form an analog loop to generate the Ipp current, and P34 mirrors out the generated IPP current.

[0041] Thus, the PTAT current source: generates a current proportional to the temperature and is usually used for temperature sensing or temperature compensation. The Poly current source: generates a current independent of temperature and is usually used for bias generation or reference generation of other circuits.

[0042] The present invention also provides a phase-locked loop with temperature compensation, including: a voltage-controlled oscillator (VCO) with a power supply voltage of (VDDVCO), which is used to generate a frequency-tunable clock signal for the phase-locked loop (PLL); a low-pass filter (LPF) that provides a filtered analog voltage control signal to the voltage-controlled oscillator unit; a charge pump (CP) that inputs or extracts current to the low-pass filter (LPF), thereby indirectly generating the control voltage signal required by the VCO..

[0043] A phase-frequency detector (PFD) is used to provide a control signal to the charge pump (CP), so that the charge pump outputs a control voltage to adjust the frequency and phase of the voltage-controlled oscillator (VCO).

[0044] The current pulse output by the charge pump passes through a low-pass filter (LPF) to filter out high-frequency components, obtaining a smooth voltage signal. This voltage signal serves as the control voltage for the VCO. The output frequency of the VCO is controlled by the input control voltage. As the control voltage changes, the output frequency of the VCO increases or decreases accordingly.

[0045] When the PFD detects that the reference signal and the feedback signal are out of sync, the charge pump adjusts the control voltage so that the output frequency of the VCO gradually locks to the same frequency as the reference signal. When the frequencies and phases of the reference signal and the feedback signal are synchronized, the UP and DOWN signals act alternately to make the control voltage reach an equilibrium value, and the VCO output frequency stabilizes at the target frequency.

[0046] The charge pump (CP) can refer to the above embodiments and will not be elaborated here.

[0047] The formula for calculating the loop bandwidth is as follows:

[0048]

[0049] The charge pump (CP) is used to close the first forward switch S1 and the second forward switch S2 when the UP signal is valid. The second current mirror above injects current into the output node Q through the first forward switch S1 to increase the control voltage. The current injected into the output node Q is Icp = m * Ipp(1 + (1 - m) / m * (1 + 0.05625 * T)). When the temperature rises, the gain Kvco of the VCO becomes smaller, which causes the loop bandwidth fc to become smaller. In the present invention, a PTAT current source is added at Icp. As the temperature rises, the current IPTAT increases, while the output current Ipp of the constant current source remains unchanged. Therefore, the current Icp (composed of IPTAT and Ipp) at the output node becomes larger. Thus, the current I output or input by the CP becomes larger, compensating for the influence of Kvco on the loop bandwidth due to temperature, and generally reducing the change in the loop bandwidth.

[0050] From the above formula, it can be seen that for a ring oscillator: as T increases, Kvco decreases, and f c decreases;

[0051] Then after compensating Icp with Iptat: as T increases, Icp increases, and f c increases;

[0052] In the present invention, the compensated Icp = m * Ipp(1 + (1 - m) / m * (1 + 0.05625 * T))

[0053] Since temperature changes can cause the gain K of the VCO vcoChanges will occur, thus causing changes in the loop bandwidth. At the same time, the magnitude of the current at the charge pump can also cause changes in the loop bandwidth. Therefore, the present invention compensates for the magnitude of the current at the charge pump to a certain extent with temperature, so as to offset the loop bandwidth changes caused by the temperature change of the VCO as much as possible as a whole.

[0054] The charge pump of the present invention combines a PTAT current and a constant current to generate a temperature-dependent charge pump. The PTAT current is a current proportional to temperature. As the temperature rises, the current increases. The constant current is a current that does not change with temperature and remains constant. By combining the PTAT current and the constant current, a temperature-dependent charge pump can be designed such that the output current of the charge pump has the desired temperature characteristics. In this embodiment, the PTAT current source generates the PTAT current. The constant current source generates the constant current.

[0055] In one embodiment, specifically, I PTAT =(kT / q)*In(mn) / R ptat , where k, q, m, n are constants in the bandgap reference circuit, and T is Fahrenheit temperature. Among them, R ptat is also a poly resistor within the chip. In actual implementation, at a certain temperature (such as 0°C = [32 + 1.8*0]°F), deliberately make the I PTAT current and the I PP current have the same magnitude, that is, (K*(32 + 1.8*0) / q)*In(mn) / R ptat =I pp . Then it can be obtained that

[0056] I ptat =I pp *(32 + 1.8*T) / (32 + 1.8*0°C), that is

[0057] I ptat =I pp *(32 + 1.8*T°C) / 32 = I pp *(1 + 0.05625*T°C)

[0058] Therefore, in Figure 3 there is I cp =m*I pp +(1 - m)*I ptat ,

[0059] That is:

[0060] Among them, 0 < m <= 1;

[0061] If m = 1, then the current I CPThe temperature compensation coefficient is 0. If m ranges from 1 to 0, then I CP In I PTAT The proportion will gradually increase. Figure 3 In it, Ictrl<2:0> is used to adjust I PTAT And I PP The proportion size.

[0062] The corresponding K is listed in the following table vco Compensation range.

[0063]

[0064] The embodiments of the present invention have been described above. The above description is exemplary, not exhaustive, and is not limited to the disclosed embodiments. Many modifications and variations are obvious to those of ordinary skill in the art without departing from the scope and spirit of the described embodiments.

Claims

1. A charge pump with temperature compensation, characterized in that: include: It includes a constant current source, a temperature-controlled current source, a proportional module and a control module, wherein the proportional module is used to combine the constant current source and the temperature-controlled current source in a certain proportion and output the combined current to the control unit; When the charge pump injects a positive current into the next stage circuit, the control module injects a current obtained by combining a constant current source and a temperature-controlled current source in a certain ratio into the next stage circuit; When the charge pump reversely extracts current from the subsequent stage, the control module extracts a current that is a combination of a constant current source and a temperature-controlled current source in a certain ratio from the subsequent stage circuit.

2. The charge pump with temperature compensation as claimed in claim 1, characterized in that: The control module includes a first current mirror connected to a negative power supply and a second current mirror connected to a positive power supply, a reference current input terminal of the first current mirror is connected to a current output terminal which is a combination of a constant current source and a temperature-controlled current source in a certain proportion, the first current output terminal is connected to the reference current input terminal of the second current mirror, and the second current output terminal is connected to the current output terminal of the second current mirror through the control module.

3. The charge pump with temperature compensation as claimed in claim 2, characterized in that: The control module also includes a first forward switch and a first reverse switch connected in series between the current output end of the second current mirror and the second current output end of the first current mirror, and the connection point of the first forward switch and the first reverse switch is connected to the next-stage low-pass filter.

4. The charge pump with temperature compensation as claimed in claim 3, characterized in that: The control module also includes a second forward switch, a second reverse switch and an operational amplifier, wherein the second forward switch and the second reverse switch are connected in series between the second current output terminal of the first current mirror and the current output terminal of the second current mirror, the positive input terminal of the operational amplifier is connected to the connection point of the first forward switch and the first reverse switch, and the negative input terminal and the output terminal are connected to the connection point of the second forward switch and the second reverse switch.

5. The charge pump with temperature compensation as claimed in claim 4, characterized in that: The temperature-controlled current source is a PTAT current source, and the proportional circuit includes: A third current mirror, used for providing a mirror current of the PTAT current source; A first current mirror group connected in parallel, for providing a proportional current of the PTAT current; a fourth current mirror, used for providing a mirror current of a constant current source; A second current mirror group connected in parallel, for providing a proportional current of the constant current; The outputs of the first current mirror group and the second current mirror group are connected to output a current that is a combination of a constant current source and a temperature-controlled current source in a certain ratio.

6. The charge pump with temperature compensation as claimed in claim 5, characterized in that: The output current of the PTAT current source is I PTAT =(kT / q)*In(mn) / R ptat , where k, q, m, n are constants, T is the temperature in Fahrenheit, R ptat It is a poly resistor inside the chip.

7. The charge pump with temperature compensation as claimed in claim 5, characterized in that: At 0°C, the output current of the PTAT current source I PTAT and the output current I of the constant current source PP , I cp =m*I pp +(1-m)*I ptat .

8. The charge pump with temperature compensation as claimed in claim 7, characterized in that: The proportional circuit also includes a gating circuit, which achieves dynamic regulation of the combined current by selecting the number of current mirrors in the first current mirror group and the second current mirror group.

9. The charge pump with temperature compensation as claimed in claim 8, characterized in that: Also includes: The gating circuit is coded in three-bit binary format, with one code corresponding to a proportional selection relationship between a constant current source and a temperature-controlled current source.

10. A phase-locked loop comprising a charge pump with temperature compensation according to any one of claims 1 to 9, characterized in that: include: Voltage controlled oscillator, low pass filter, charge pump and phase frequency detector; The charge pump includes a constant current source, a temperature-controlled current source, a control module, and a proportional module. The proportional module is used to combine the constant current source and the temperature-controlled current source in a certain ratio and output the combined current to the control unit; When the charge pump outputs positively to the low-pass filter, the control module inputs a current obtained by combining a constant current source and a temperature-controlled current source in a certain ratio to the low-pass filter; When the charge pump reverses the current from the low-pass filter, the control module extracts the current that is a combination of the constant current source and the temperature-controlled current source in a certain ratio from the low-pass filter.

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