CN104090625B - A kind of current mirror for low supply voltage - Google Patents

Abstract

The present invention relates to technical field of integrated circuits, relate to a kind of current mirror specifically.Current mirror of the present invention, is characterized in that, this current mirror by PMOS MP1, MP2, NMOS tube MN1, electric capacity C1, C2, resistance R1, input current source, output end current source and bias current sources are formed; Wherein, the source electrode of MP1 meets power supply VCC, and its grid connects the grid of MP2, and its drain electrode connects the positive pole of input current source; The minus earth VSS of input current source; The drain electrode of MN1 meets power supply VCC, and its grid connects the positive pole of input current source, and its source electrode connects the positive pole of bias current sources, and its substrate connects the tie point of MP1 grid and MP2 grid by R1; The tie point of the source electrode of MP1 and the drain electrode of MN1 connects the tie point of MN1 grid and input current source positive pole successively by C1, C2; The source electrode of MP2 meets power supply VCC, and its drain electrode connects the positive pole of output current source.Beneficial effect of the present invention is, is applicable to using at low supply voltages; Also improve the PSR of current mirror simultaneously.The present invention is particularly useful for current mirroring circuit.

Description

A kind of current mirror for low supply voltage

Technical field

The present invention relates to technical field of integrated circuits, relate to a kind of current mirror specifically.

Background technology

Current mirror is an important circuit unit in mimic channel, and it both as bias unit, also as signal processing unit, can be widely used in mimic channel and radio circuit.

Fig. 1 is existing a kind of current mirroring circuit schematic diagram, by input current source I _in, output current source I _outform with PMOS MP1, MP2.Wherein, grid and the drain electrode short circuit of MP1 pipe, the overdrive voltage of such MP1 pipe is:

V _OV1＝V _SG1-|V _THP1|

And the source-drain voltage of MP1 pipe is:

V _SD1＝V _SG1

Wherein | V _tHP1| be the absolute value of the threshold voltage of PMOS MP1, V _sG1for the voltage between MP1 pipe source electrode to grid.V can be found out from two formulas above _sD1than the overdrive voltage V of MP1 pipe _oV1the absolute value of the threshold voltage of a large PMOS MP1, this causes the minimizing of voltage remaining, and therefore this traditional current mirroring circuit is not suitable for working at low supply voltages.

Summary of the invention

Object of the present invention, is not suitable for the problem worked at low supply voltages exactly for above-mentioned conventional current mirror circuit, propose a kind of current mirror being applicable to low supply voltage.

Technical scheme of the present invention is, a kind of current mirror for low supply voltage, is characterized in that, this current mirror by PMOS MP1, MP2, NMOS tube MN1, electric capacity C1, C2, resistance R1, input current source, output end current source and bias current sources are formed; Wherein, the source electrode of MP1 meets power supply VCC, and its grid connects the grid of MP2, and its drain electrode connects the positive pole of input current source; The minus earth VSS of input current source; The drain electrode of MN1 meets power supply VCC, and its grid connects the positive pole of input current source, and its source electrode connects the positive pole of bias current sources, and its substrate connects the tie point of MP1 grid and MP2 grid by R1; The minus earth VSS of bias current sources; The tie point of the source electrode of MP1 and the drain electrode of MN1 connects the tie point of MN1 grid and input current source positive pole successively by C1, C2; The source electrode of MP2 meets power supply VCC, and its drain electrode connects the positive pole of output current source; The minus earth VSS of output current source.

Beneficial effect of the present invention is, is applicable to using at low supply voltages; Also improve the PSR (suppression to power supply noise) of current mirror simultaneously.

Accompanying drawing explanation

Fig. 1 is traditional current-mirror structure schematic diagram;

Fig. 2 is current-mirror structure schematic diagram of the present invention.

Embodiment

Below in conjunction with accompanying drawing, the specific embodiment of the present invention is described

As shown in Figure 2, current mirror of the present invention, by PMOS MP1, MP2, NMOS tube MN1, electric capacity C1, C2, resistance R1, input current source, output end current source and bias current sources are formed; Wherein, the source electrode of MP1 meets power supply VCC, and its grid connects the grid of MP2, and its drain electrode connects the positive pole of input current source; The minus earth VSS of input current source; The drain electrode of MN1 meets power supply VCC, and its grid connects the positive pole of input current source, and its source electrode connects the positive pole of bias current sources, and its substrate connects the tie point of MP1 grid and MP2 grid by R1; The minus earth VSS of bias current sources; The tie point of the source electrode of MP1 and the drain electrode of MN1 connects the tie point of MN1 grid and input current source positive pole successively by C1, C2; The source electrode of MP2 meets power supply VCC, and its drain electrode connects the positive pole of output current source; The minus earth VSS of output current source.

Compared with existing current mirror, the grid of MP1 pipe is not shorted to drain electrode, but by the drain voltage of MP1 pipe through one by NMOS tube MN1 and bias current sources I _bthe source formed reduces the gate source voltage V of a MN1 pipe with amplifier _gS1, a large resistance of then connecting, be connected to the grid of MP1 pipe, source is operated in subthreshold region with the NMOS tube MN1 in amplifier, the V of MN1 pipe _gS1approximate greatly the threshold voltage V of this NMOS tube _tHN1, because the threshold voltage V of NMOS tube _tHN1be less than the absolute value of the threshold voltage of PMOS MP1 | V _tHP1|, MP1 therefore can be made to manage and to be still operated in saturation region, realize current mirror principle.The drain voltage of MP1 pipe is improve V simultaneously _tHN1, the voltage between MP1 pipe source electrode to drain electrode reduces V _tHN1.Voltage between MP1 pipe source electrode to drain electrode is:

V _SD(MP1)≈V _SG(MP1)-V _THN1(1)

V in formula (1) _{sG (MP1)}represent the voltage between MP1 pipe source electrode to grid.

Such current mirror has saved V _tHN1voltage remaining, make current mirror be particularly suitable for working at low supply voltages.

The present invention has the characteristic of high PSR, and electric capacity C1 is the same with existing current mirror, power supply noise is coupled to the grid of PMOS, improves the PSR of current mirror.But by NMOS tube MN1 and bias current sources I _bthis branch road of composition, it is larger that this point of the source electrode of MN1 pipe is subject to power supply noise impact.The power path of the power path utilizing electric capacity C1 and C2 to form and the drain electrode of MN1 pipe, known

${\tilde{V}}_{S\left(\mathrm{MN}1\right)}\≈{\tilde{V}}_{\mathrm{CC}}\frac{R_1+1/s(C_1+C_2)}{1/g_{m\left(\mathrm{MN}1\right)}+R_1+1/s(C_1+C_2)}\≈{\tilde{V}}_{\mathrm{CC}}---\left(2\right)$

Here introduce a large resistance R1, reduce MP1 pipe and the dividing potential drop of MP2 tube grid to the power supply noise of this point of MN1 pipe source electrode.

${\tilde{V}}_{G(\mathrm{MP}1,\mathrm{MP}2)}\≈{\tilde{V}}_{S\left(\mathrm{MN}1\right)}/[s{R}_1(C_1+C_2)+1]+{\tilde{V}}_{\mathrm{CC}}\{s{R}_1(C_1+C_2)/[s{R}_1(C_1+C_2)+1\left]\right\}---\left(3\right)$

By formula (2) and formula (3), can show that the impact that the grid of MP1 and MP2 is subject to power supply noise is:

${\tilde{V}}_{G(\mathrm{MP}1,\mathrm{MP}2)}\≈{\tilde{V}}_{\mathrm{CC}}---\left(4\right)$

In formula (2) ~ (4) refer to power supply noise, with the grid representing MN1 pipe source electrode and MP1 and MP2 is respectively subject to the voltage small-signal of impact, g _{m (MN1)}refer to the mutual conductance of MN1 pipe.Can show that the gain that affects that MP1 manages and the grid of MP2 pipe is subject to power supply noise is approximately 1 by formula (4), then ensure that MP1 manages and the gate source voltage of MP2 pipe is all close to zero in all frequency ranges, improve the PSR of current mirror.

In addition, electric capacity C2 and MP1 constitutes miller-compensated structure, in conjunction with electric capacity C1, arranges MP1 tube grid in order to bulky capacitor node.In the setting by large resistance R1, the dominant pole of the feedback control loop in this structure can be arranged on the grid of MP1 pipe, ensure the steady operation of system.

Claims (1)

1., for a current mirror for low supply voltage, it is characterized in that, this current mirror by PMOS MP1, MP2, NMOS tube MN1, electric capacity C1, C2, resistance R1, input current source, output current source and bias current sources are formed; Wherein, the source electrode of MP1 meets power supply VCC, and its grid connects the grid of MP2, and the drain electrode of MP1 connects the positive pole of input current source; The minus earth VSS of input current source; The drain electrode of MN1 meets power supply VCC, and its grid connects the positive pole of input current source, and its source electrode connects the positive pole of bias current sources, and its substrate connects the tie point of MP1 grid and MP2 grid by R1; The minus earth VSS of bias current sources; The tie point of the source electrode of MP1 and the drain electrode of MN1 connects the tie point of MN1 grid and input current source positive pole successively by C1, C2; The source electrode of MP2 meets power supply VCC, and its drain electrode connects the positive pole of output current source; The minus earth VSS of output current source.