CN101895192A

CN101895192A - Charge pump capable of solving problems of charge distribution and current mismatching

Info

Publication number: CN101895192A
Application number: CN 201010241851
Authority: CN
Inventors: 梅海涛; 孙礼中
Original assignee: SUZHOU COSINE MICROELECTRONICS TECHNOLOGY Co Ltd
Current assignee: SUZHOU COSINE MICROELECTRONICS TECHNOLOGY Co Ltd
Priority date: 2010-07-30
Filing date: 2010-07-30
Publication date: 2010-11-24

Abstract

The invention relates to a charge pump capable of solving problems of charge distribution and current mismatching. The charge pump is provided with a charge pump core circuit, a current copy feedback circuit, and a seventh NMOS transistor. The charge pump core circuit comprises a differential charge pump input structure, a first PMOS transistor, a first NMOS transistor and an operational amplifier, wherein the differential charge pump input structure consists of a sixth PMOS transistor, a seventh PMOS transistor, an eighth PMOS transistor and a ninth PMOS transistor. A grid of a third NMOS transistor is connected with a positive input end of the operational amplifier; the source and grid of a third PMOS transistor are connected with the sources and grids of the first PMOS transistor and a second PMOS transistor respectively; the source and grid of a fifth NMOS transistor are connected with the sources and grids of the first NMOS transistor and a second NMOS transistor respectively; the grid of a fourth NMOS transistor is connected with the drain of a fifth PMOS transistor; and the drains and sources of the third PMOS transistor and the fourth PMOS transistor are in short circuit. The grid and source of the seventh NMOS transistor are connected with the grid and source of the first NMOS transistor. The charge pump cannot generate ripple vibration, can realize perfect charging and discharging current matching, and has the advantages of simple structure and convenient operation.

Description

A kind of charge pump that solves charge distributing and current mismatch problem

Technical field:

The present invention relates to a kind of charge pump that solves charge distributing and current mismatch problem, be used for phase-locked loop (PLL).

Background technology:

In Fig. 1 phase-locked loop (PLL), the signal of phase discriminator (PFD) input is respectively the clock of reference clock and divider output, PFD compares by frequency and the phase place to two signals, produce error signal UP and DN, error signal just can generate the direct-current control voltage VCTRL that is used for controlling voltage-controlled oscillator (VCO) (VCO) output frequency by charge pump and loop filter.This is an automatic feedback system, and when this reponse system locking, REF_CLK=DIV_CLK=OUT_CLK/M has also just realized the purpose by a high-frequency signal of a low frequency signal generation.As very crucial part in the pll system, the design of charge pump can run into two major issues usually: charge distributing and current mismatch.

When UP=1, M1 is in cut-off state among Fig. 1, and the N1 point connects current source, be used for realizing that the common area of transistor of current source is bigger, so parasitic capacitance is also bigger, accumulates in the N1 point with regard to having a large amount of electric charges like this.The voltage of VCTRL can be subjected to phase-locked loop control and change when M1 is in cut-off state, when UP signal during by high step-down, the M1 conducting, in the moment of conducting, if the voltage that the voltage of VCTRL and N1 are ordered is unequal, just will inevitably cause the electric charge between VCTRL and the N1 to be redistributed at 2, the result that this electric charge is redistributed produces ripple at VCTRL voltage, this ripple can make the VCO signal irregular chatterin occur, thus the noiseproof feature of grievous injury output clock.Also there is identical problem at M2 with N2 one end, the charge distributing problem of Here it is charge pump.

In addition, variation along with VCTRL voltage, M1, M2 and being used for realizes that the transistorized Vds of two current sources can change up and down, because transistorized output impedance can not be infinitely great in the practical application, output characteristic curve certainly exists certain slope, therefore at different VCTRL voltage, the charging current Iup of charge pump and discharging current Idn just can not equate and mate fully, so-called current mismatch problem that Here it is.Current mismatch can produce static shift in pll system, this static shift can influence the noiseproof feature of system equally.

Summary of the invention:

In order to solve the problems of the technologies described above, the invention provides a kind of charge pump that solves charge distributing and current mismatch problem.

The technical solution adopted for the present invention to solve the technical problems is: a kind of charge pump that solves charge distributing and current mismatch problem is provided with:

The charge pump core circuit, comprise the differential charge pump input structure of forming by the 6th PMOS pipe, the 7th PMOS pipe and the 8th NMOS pipe, the 9th NMOS pipe, the source electrode of described the 6th PMOS pipe, the 7th PMOS pipe links to each other with the drain electrode of a PMOS pipe, the source electrode of described the 8th NMOS pipe, the 9th NMOS pipe links to each other with the drain electrode of a NMOS pipe, the drain electrode of the 6th PMOS pipe, the 8th NMOS pipe is connected on the positive input terminal of operational amplifier, and the negative input end of its transportation amplifier is connected with the output short circuit and with the drain electrode of the 7th PMOS pipe, the 9th NMOS pipe;

The current replication feedback circuit, the grid of its 3rd NMOS pipe is connected with the positive input terminal of operational amplifier, the source of the 3rd PMOS pipe, grid are connected with PMOS pipe, the source of the 2nd PMOS pipe, grid respectively, the deleting of the 5th NMOS pipe, source electrode are connected with the deleting of NMOS pipe, the 2nd NMOS pipe, source terminal respectively, the grid of the 4th NMOS pipe is connected in the drain electrode of the 5th PMOS pipe, the leakage of described the 3rd PMOS pipe and the 4th PMOS pipe, grid be short circuit all, and the grid of the source electrode of the 4th PMOS pipe and the 6th NMOS pipe connects power supply;

And delete, the deleting of source electrode and a NMOS pipe, the 7th NMOS pipe that source electrode is connected, leakage, the grid of described the 7th NMOS pipe connect external current source.

Further: described PMOS pipe and the 2nd PMOS pipe measure-alike, a NMOS are managed and the 2nd NMOS pipe measure-alike.

The present invention not only can not produce the ripple shake on VCTRL, can also realize perfect charging and discharging currents coupling, and simple in structure, easy to operate.

Description of drawings:

Fig. 1 is the phase-locked loop circuit schematic diagram.

Fig. 2 is the charge pump core circuit.

Fig. 3 has adopted the circuit diagram that duplicates feedback current source and the combination of unit gain operational amplifier.

Fig. 4 is a circuit diagram of the present invention.

Among the figure: 1, PMOS pipe; 2, the 2nd PMOS pipe; 3, the 3rd PMOS pipe; 4, the 4th PMOS pipe; 5, the 5th PMOS pipe; 6, operational amplifier; 7, NMOS pipe; 8, the 2nd NMOS pipe; 9, the 3rd NMOS pipe; 10, the 4th NMOS pipe; 11, the 5th NMOS pipe; 12, the 6th NMOS pipe; 13, the 7th NMOS pipe; 14, the 6th PMOS pipe; 15, the 7th PMOS pipe; 16, the 8th NMOS pipe; 17, the 9th NMOS pipe.

Embodiment:

The present invention is further described below in conjunction with drawings and Examples.

The circuit structure of Fig. 2 can be with the problem that solves charge distributing, as shown in Figure 2, its inside is provided with operational amplifier, the positive input terminal of described operational amplifier is connected with two branch roads of differential charge pump input structure respectively with output, and its negative input end and output short circuit are to form unity gain buffer.The PFD output signal adopts difference form, when UP=high, M1 is in cut-off state, but UPB=low, M4 then is in conducting state, therefore the voltage of N1 point voltage and VCTRLDUM equates all the time, because the employing of the operational amplifier among Fig. 2 is the connected mode of unity gain buffer, makes no matter how VCTRL changes, the voltage of VCTRLDUM is all followed VCTRL and is changed, that is to say, under any state, N1, it is equal that the voltage of VCTRLDUM and VCTRL all keeps, therefore when UP signal during by high step-down, because voltage identical, can not produce the redistributing of electric charge between VCTRL and the N1 at 2, just can on VCTRL, not produce ripple yet and shake.

And the problem of current mismatch mainly is owing to the variation along with VCTRL voltage, and transistorized Vds can change, and therefore causes the charging current Iup of charge pump and discharging current Idn not to equate fully and to mate.Adopted among Fig. 3 and duplicated the mode that feedback current source and unit gain operational amplifier combine, can address this problem effectively.As shown in Figure 3, if M4=M8, the bias current of M4 and M8 equates, just Idn=Irp.Wherein Irp had both flow through M8 and had also flow through M5.When VCTRL changed, operational amplifier forced Vx to follow VCTRL, so the bias voltage Vgs of M1 and M5 and Vds can equate all the time, and as long as like this M1=M5, Irp just equals Iup all the time.Even, also can guarantee Iup=Irp=Idn so Vctrl constantly changes.In this way, charge pump has just been realized perfect charging and discharging currents coupling.

Fig. 4 is a circuit diagram of the present invention.It comprises: the charge pump core circuit, comprise by the 6th PMOS pipe 14, the 7th PMOS pipe the 15 and the 8th NMOS pipe 16, the differential charge pump input structure that the 9th NMOS pipe 17 is formed, described the 6th PMOS pipe 14, the source electrode of the 7th PMOS pipe 15 links to each other with the drain electrode of PMOS pipe 1, described the 8th NMOS pipe 16, the source electrode of the 9th NMOS pipe 17 links to each other with the drain electrode of NMOS pipe 7, the 6th PMOS pipe 14, the drain electrode of the 8th NMOS pipe 16 is connected on the positive input terminal of operational amplifier 6, the negative input end of its transportation amplifier 6 and output short circuit and with the 7th PMOS pipe 15, the drain electrode of the 9th NMOS pipe 17 connects; The current replication feedback circuit, the grid of its 3rd NMOS pipe 9 is connected with the positive input terminal of operational amplifier 6, the source of the 3rd PMOS pipe 3, grid are connected with source, the grid of PMOS pipe the 1, the 2nd PMOS pipe 2 respectively, the deleting of the 5th NMOS pipe 11, source electrode are connected with the deleting of NMOS pipe the 7, the 2nd NMOS pipe 8, source terminal respectively, the grid of the 4th NMOS pipe 10 is connected in the drain electrode of the 5th PMOS pipe 5, the leakage of described the 3rd PMOS pipe the 3 and the 4th PMOS pipe 4, grid be short circuit all, and the grid of the source electrode of the 4th PMOS pipe 4 and the 6th NMOS pipe 12 connects power supply; And delete, the deleting of source electrode and NMOS pipe 7, the 7th NMOS pipe 13 that source electrode is connected, leakage, the grid of described the 7th NMOS pipe 13 connect external current source.Wherein the charge pump core circuit is identical with the structure of Fig. 2, eliminate electric charge with amplifier and share, other parts then with Fig. 3 in structural similarity, only the amplifier among Fig. 3 is replaced by the differential pair among Fig. 4.By this differential amplifier, feedback circuit makes the voltage follow VCTRL of Vx, thereby realizes Iup=Irp=Idn.

It is emphasized that: above only is preferred embodiment of the present invention, be not that the present invention is done any pro forma restriction, every foundation technical spirit of the present invention all still belongs in the scope of technical solution of the present invention any simple modification, equivalent variations and modification that above embodiment did.

Claims

1. charge pump that can solve charge distributing and current mismatch problem, it is characterized in that: described charge pump is provided with:

The charge pump core circuit, comprise by the 6th PMOS pipe (14), the 7th PMOS pipe (15) and the 8th NMOS pipe (16), the differential charge pump input structure that the 9th NMOS pipe (17) is formed, described the 6th PMOS pipe (14), the source electrode of the 7th PMOS pipe (15) links to each other with the drain electrode that a PMOS manages (1), described the 8th NMOS pipe (16), the source electrode of the 9th NMOS pipe (17) links to each other with the drain electrode that a NMOS manages (7), the 6th PMOS manages (14), the drain electrode of the 8th NMOS pipe (16) is connected on the positive input terminal of operational amplifier (6), the negative input end of its transportation amplifier (6) and output short circuit and with the 7th PMOS pipe (15), the drain electrode of the 9th NMOS pipe (17) connects;

The current replication feedback circuit, the grid of its 3rd NMOS pipe (9) is connected with the positive input terminal of operational amplifier (6), the source of the 3rd PMOS pipe (3), grid is managed (1) with a PMOS respectively, the source of the 2nd PMOS pipe (2), grid connects, deleting of NMOS pipe (11), source electrode is managed (7) with a NMOS respectively, deleting of the 2nd NMOS pipe (8), source terminal connects, the grid of the 4th NMOS pipe (10) is connected in the drain electrode of the 5th PMOS pipe (5), the leakage of described the 3rd PMOS pipe (3) and the 4th PMOS (4) pipe, grid is short circuit all, and the grid of the source electrode of the 4th PMOS pipe (4) and the 6th NMOS pipe (12) connects power supply;

And delete, source electrode and a NMOS manage the deleting of (7), source electrode is connected the 7th NMOS pipe (13), leakage, the grid of described the 7th NMOS pipe (13) connect external current source.

2. the charge pump that solves charge distributing and current mismatch problem according to claim 1 is characterized in that: described PMOS pipe (1) and the 2nd PMOS manage the measure-alike of (2), and NMOS pipe (7) and the 2nd NMOS manage the measure-alike of (8).