CN104506151A - An operational amplifier for medical electronics - Google Patents

Abstract

The invention discloses an operational amplifier for medical electronics, wherein, a three-stage operational amplifier is compensated in a single-capacitor-embedded compensation mode, a gain bandwidth product of the operational amplifier is expanded, and also constant bias current is generated by adopting a PMOS pipe, to increase transconductance of a current-amplifier-embedded and reduce a quality factor of a conjugate pair of secondary poles of the operational amplifier. In the case that the operational amplifier is in specific work, in the case of a low frequency, the operational amplifier provides high gain through three gain-stages; and in the case of intermediate and high frequencies, a compensation capacitor Cc couples a variation of an output signal VOUT, and the coupled signal is amplified, is sent to an output end of a first stage of the operational amplifier, is amplified further by a second stage and a third stage, and then is returned to the output end VOUT, to reduce the variation of the original signal. According to the operational amplifier for medical electronics, the three-stage operational amplifier is small in compensation capacitance, is high in the gain bandwidth product, and can greatly enhance, with low power consumption, the capacity that the operational amplifier drives a capacitive load.

Description

A kind of operational amplifier for medical electronics

Technical field

The invention belongs to electronic circuit technology field, more specifically say, relate to a kind of operational amplifier for medical electronics.

Background technology

Operational amplifier is one of basic module of analog circuit and system.System needs the operational amplifier of high-gain, high bandwidth and wide output area.Along with the lifting of technique, metal-oxide-semiconductor channel length reduces, and maximum withstand voltage reduction, op-amp gain and output area also reduce thereupon.Multi-stage operational amplifier can improve amplifier gain and increase output area, but casacade multi-amplifier introduces extra low-frequency pole, usually needs compensation technique to remain stable.Especially, in the application of some medical electronics, need to drive bulky capacitor, limit by system power dissipation simultaneously, the quiescent dissipation of operational amplifier must be low as far as possible, in addition in order to reduce system response time, the switching rate of operational amplifier can not be compromised, and this application needs three-stage operational amplifier.

Document " Low-voltage operational amplifier with rail-to-rail input and outputstages (IEEE J.Solid-State Circuits; 1985; 20 (12): 1144 – 1150) " proposes first item three-stage operational amplifier, have employed Nested Miller compensation mode.But, when driving identical capacitive load, the maximum accessible gain bandwidth product of Nested Miller compensation three-stage operational amplifier is only 1/4th of one-stage amplifier, is all directly proportional to load capacitance based on Nested Miller compensation three-stage operational amplifier miller capacitance value.Drive in large capacitive load application, need large-area Miller integrated capacitance based on Nested Miller compensation three-stage operational amplifier, this not only can increase chip area, causes system cost significantly to increase, and also can reduce frequency response and the transient response characteristic of system.

Document " Advances in active-feedback frequency compensation with poweroptimization and transient improvement (IEEE Trans.Circuits Syst.I; 2004; 51 (9): 1690 – 1696) " proposes the three-stage operational amplifier compensated based on active frequencies, this technology kind makes miller capacitance value be directly proportional to the square root of load capacitance, the capacitance of building-out capacitor reduces greatly, and gain bandwidth sum switching rate obviously increases simultaneously.But be still carried between the output of amplifier and the amplifier second level in the second miller capacitance of the three-stage operational amplifier of active frequencies compensation, non-dominant pole frequency is restricted.

Summary of the invention

The object of the invention is to overcome the deficiencies in the prior art, a kind of operational amplifier for medical electronics is provided, the embedded compensation way of single capacitor is adopted to compensate three-stage operational amplifier, expand the gain bandwidth product of operational amplifier, adopt PMOS to produce constant-current bias simultaneously and increase the mutual conductance of nested current amplifier, reduce the quality factor that operational amplifier conjugation time limit is right, improve frequency characteristic and the transient response performance of operational amplifier.

For achieving the above object, a kind of operational amplifier for medical electronics of the present invention, comprise the biasing circuit, first order amplifying circuit, second level amplifying circuit and the third level amplifying circuit that connect successively, it is characterized in that, the first order to third level amplifying circuit connects a building-out capacitor Cc, this building-out capacitor Cc one end concatenation operation amplifier out, the other end is connected to the efferent duct grid of first order amplifying circuit.

Further, described biasing circuit comprises: PMOS M _p11with outside constant-current bias source I _b;

PMOS M _p11source electrode connect supply voltage V _dD, PMOS M _p11grid be connected to outside constant-current bias source IB, PMOS M _p11grid, PMOS M _p11drain electrode and PMOS M _p2grid be all connected, for generating the constant bias voltage V of PMOS _bP;

Described first order amplifying circuit comprises: PMOS M _p1, PMOS M _p2, PMOS M _p3, PMOS M _p4, PMOS M _p5, PMOS M _p6, PMOS M _p7, NMOS tube M _n1, NMOS tube M _n2, NMOS tube M _n3, NMOS tube M _n4with building-out capacitor Cc;

PMOS M _p1, PMOS M _p2, PMOS M _p3, PMOS M _p6, PMOS M _p7source electrode connect supply voltage V respectively _dD;

PMOS M _p1grid, PMOS M _p2grid, PMOS M _p3grid be connected with outside constant-current bias source IB;

PMOS M _p1drain electrode, PMOS M _p4source electrode, PMOS M _p5source electrode is connected;

PMOS M _p2drain electrode, PMOS M _p4drain electrode, NMOS tube M _n1drain electrode, NMOS tube M _n1grid, NMOS tube M _n4grid be connected with building-out capacitor Cc one end;

PMOS M _p3drain electrode, PMOS M _p5drain electrode, NMOS tube M _n2drain electrode, NMOS tube M _n2grid, NMOS tube M _n3grid, and NMOS tube M in the second amplifier _n6grid be connected;

NMOS tube M _n3drain electrode and PMOS M _p6grid, PMOS M _p6drain electrode, PMOS M _p7grid be connected;

NMOS tube M _n4drain electrode and PMOS M _p7drain electrode, PMOS M in the amplifier of the second level _p8grid, PMOS M _p9grid be connected;

NMOS tube M _n1source electrode, NMOS tube M _n2source electrode, NMOS tube M _n3source electrode, NMOS tube M _n4source electrode respectively ground connection;

Described second level amplifying circuit comprises PMOS M _p8, PMOS M _p9with NMOS tube M _n5, NMOS tube M _n6;

PMOS M _p8grid and PMOS M _p9grid be connected, then with PMOS M _p7drain electrode and the first amplifier in NMOS tube M _n4drain electrode be connected;

PMOS M _p8drain electrode, NMOS tube M _n5drain electrode, NMOS tube M _n5grid, NMOS tube M in third level amplifier _n7grid be connected;

PMOS M _p8, PMOS M _p9source electrode be connected respectively to supply voltage V _dD;

PMOS M _p9drain electrode, NMOS tube M _n6drain electrode, PMOS M in third level amplifier _p10grid be connected;

NMOS tube M _n6grid and the first amplifier in PMOS M _p3drain electrode, PMOS M _p5drain electrode, NMOS tube M _n2drain electrode, NMOS tube M _n2grid, NMOS tube M _n3grid be connected;

NMOS tube M _n5, NMOS tube M _n6source electrode respectively ground connection;

Described third level amplifying circuit comprises PMOS MP ₁₀with NMOS tube M _n7;

PMOS M _p10source electrode be connected to supply voltage V _dD;

PMOS M _p10grid and second level amplifier in PMOS M _p9drain electrode, NMOS tube M _n6drain electrode be connected;

PMOS M _p10drain electrode and NMOS tube M _n7drain electrode, the building-out capacitor Cc other end be connected and be linked into the output V of operational amplifier _oUT;

Goal of the invention of the present invention is achieved in that

A kind of operational amplifier for medical electronics of the present invention, the embedded compensation way of single capacitor is adopted to compensate three-stage operational amplifier, expand the gain bandwidth product of operational amplifier, adopt PMOS to produce constant-current bias simultaneously and increase the mutual conductance of nested current amplifier, reduce the quality factor that operational amplifier conjugation time limit is right.Operational amplifier is when specific works, and when low frequency, operational amplifier provides very high gain by 3 gain stages; At high frequency, building-out capacitor Cc coupled output signal V _oUTchange, after amplifying, be sent to the output of the operational amplifier first order, the second level and the third level amplify this signal further, then turn back to output V _oUT, to reduce the change of original signal.Three-stage operational amplifier building-out capacitor of the present invention is little, and gain bandwidth product is high, significantly can promote operational amplifier and drive capacitance load capability under low-power consumption.

Meanwhile, a kind of operational amplifier for medical electronics of the present invention also has following beneficial effect:

(1), improve as a step of the present invention, the first order to third level amplifying circuit increase only a building-out capacitor Cc, by single capacitor embedded compensation way, three-stage operational amplifier is compensated, which reduce building-out capacitor, improve gain bandwidth, significantly promote operational amplifier under making low-power consumption and drive capacitance load capability, also a saving cost.

(2), when low frequency, operational amplifier provides very high gain by 3 gain stages; At high frequency, building-out capacitor Cc coupled output signal V _oUTchange, after amplifying, be sent to the output of the operational amplifier first order, the second level and the third level amplify this signal further, then turn back to output V _oUT, to reduce the change of original signal.

Accompanying drawing explanation

Fig. 1 is a kind of logical construction schematic diagram of the operational amplifier for medical electronics;

Fig. 2 is a kind of a kind of implementing circuit figure of the operational amplifier for medical electronics;

Fig. 3 is a kind of frequency response characteristic the result of the operational amplifier for medical electronics;

Fig. 4 is a kind of transient response characteristic the result of the operational amplifier for medical electronics.

Embodiment

Below in conjunction with accompanying drawing, the specific embodiment of the present invention is described, so that those skilled in the art understands the present invention better.Requiring particular attention is that, in the following description, when perhaps the detailed description of known function and design can desalinate main contents of the present invention, these are described in and will be left in the basket here.

Embodiment

Fig. 1 is a kind of logical construction schematic diagram of the operational amplifier for medical electronics.

In the present embodiment, as shown in Figure 1, the logical construction of operational amplifier comprises three each and every one mutual conductance amplifying stages.First order mutual conductance is g _m1, output resistance is R ₁, output capacitance is C ₁.Second level mutual conductance is g _m2, output resistance is R ₂, output capacitance is C ₂.Third level mutual conductance is g _m3, output resistance is R ₁, output capacitance is C ₃.

G _mithe mutual conductance of input transistors, g _mcthe mutual conductance of nested current amplifier, g _mf1and g _mf2constitute two feedforward levels, they only for increasing the switching rate of the operational amplifier second level and the third level, improve mapping, do not affect frequency response.C _cfor building-out capacitor, C _lbe load capacitance, operational amplifier small-signal transfer function of the present invention is:

$\frac{V_{\mathrm{out}}}{V_{\mathrm{in}}}\left(s\right)=\frac{g_{m1}{R}_1{g}_{m2}{R}_2{g}_{m3}{R}_3(1+s\frac{C_c}{{2g}_{\mathrm{mc}}})}{(1+{\mathrm{sR}}_1{g}_{m2}{R}_2{g}_{m3}{R}_3{C}_c)(1+s\frac{C_L{C}_1}{g_{m2}{R}_2{g}_{m3}{C}_c}+s^2\frac{C_L{C}_1}{g_{m2}{R}_2{g}_{m3}{g}_{\mathrm{mc}}})(1+{\mathrm{sR}}_2{C}_2)}---\left(1\right)$

The gain bandwidth product GBW of operational amplifier is:

$\mathrm{GBW}=\frac{g_{m1}}{C_c}---\left(2\right)$

By the transfer function shown in formula (1), the secondary limit of operational amplifier and relevant zero point can be derived, specifically as shown in formula (3) to (5).Wherein, second time limit p ₂with third time limit p ₃define complex poles pair, their frequency and corresponding quality factor Q value as shown in formula (3) and (4), and shown in formula (5) second zero point z ₂for improving the phase margin of system.

$\left|p_{\mathrm{2,3}}\right|=\sqrt{\frac{g_{m2}{R}_2{g}_{m3}{g}_{\mathrm{mc}}}{C_L{C}_1}}---\left(3\right)$

$Q=\sqrt{\frac{{C_c}^2{g}_{m2}{R}_2{g}_{m3}}{g_{\mathrm{mc}}{C}_L{C}_1}}---\left(4\right)$

$z_2=\frac{{2g}_{\mathrm{mc}}}{C_c}---\left(5\right)$

By by load capacitance, the gain bandwidth product GBW of operational amplifier determines that time limit affects, the secondary pole frequency that the three-stage operational amplifier of Nested Miller compensation mode is determined by load capacitance is:

$p_3=\frac{g_{m3}}{C_L}---\left(6\right)$

The secondary pole frequency that operational amplifier is determined by load capacitance is:

$p_3=\frac{g_{m2}{R}_2{g}_{m3}}{C_L}---\left(7\right)$

Compare with the three-stage operational amplifier of traditional Nested Miller compensation mode, the secondary limit determined by load capacitance has been raised g by the operational amplifier that the present invention proposes _m2r ₂doubly, therefore frequency response characteristic significantly increases, and building-out capacitor area and quiescent current significantly reduce.

In order to ensure that operational amplifier is stable under wide load capacitance, the frequency that complex poles is right | p _2,3| to design gain bandwidth product GBW's doubly.In order to avoid frequency domain spike, quality factor Q value is can derive, building-out capacitor value and nested current amplifier mutual conductance g _mcbe respectively:

$C_c=1.3\sqrt{\frac{g_{m1}{C}_L{C}_1}{g_{m2}{R}_2{g}_{m3}}}---\left(8\right)$

$g_{\mathrm{mc}}=2\sqrt{3}{g}_{m1}---\left(9\right)$

Fig. 2 is a kind of a kind of implementing circuit figure of the operational amplifier for medical electronics.

In the present embodiment, in order to ensure while, do not reduce the input voltage range of operational amplifier, the present invention adopts PMOS M _p2and M _p3additional bias current is provided, thus increases nested current amplifier mutual conductance g _mc, reduce the quality factor that operational amplifier conjugation time limit is right.

A kind of operational amplifier for medical electronics, comprise: the biasing circuit connected successively, first order amplifying circuit, second level amplifying circuit and third level amplifying circuit, and a building-out capacitor Cc is connected in the first order to third level amplifying circuit, this building-out capacitor Cc one end concatenation operation amplifier out, the other end is connected to the efferent duct grid of first order amplifying circuit.

Wherein, biasing circuit comprises: PMOS M _p11with outside constant-current bias source I _b;

PMOS M _p11source electrode connect supply voltage V _dD, PMOS M _p11grid be connected to outside constant-current bias source IB, PMOS M _p11grid, PMOS M _p11drain electrode and PMOS M _p2grid be all connected, for generating the constant bias voltage V of PMOS _bP;

First order amplifying circuit comprises: PMOS M _p1, PMOS M _p2, PMOS M _p3, PMOS M _p4, PMOS M _p5, PMOS M _p6, PMOS M _p7, NMOS tube M _n1, NMOS tube M _n2, NMOS tube M _n3, NMOS tube M _n4with building-out capacitor Cc;

PMOS M _p1, PMOS M _p2, PMOS M _p3, PMOS M _p6, PMOS M _p7source electrode connect supply voltage V respectively _dD;

PMOS M _p1grid, PMOS M _p2grid, PMOS M _p3grid be connected with outside constant-current bias source IB;

PMOS M _p1drain electrode, PMOS M _p4source electrode, PMOS M _p5source electrode is connected;

PMOS M _p2drain electrode, PMOS M _p4drain electrode, NMOS tube M _n1drain electrode, NMOS tube M _n1grid, NMOS tube M _n4grid be connected with building-out capacitor Cc one end;

PMOS M _p3drain electrode, PMOS M _p5drain electrode, NMOS tube M _n2drain electrode, NMOS tube M _n2grid, NMOS tube M _n3grid, and NMOS tube M in the second amplifier _n6grid be connected;

NMOS tube M _n3drain electrode and PMOS M _p6grid, PMOS M _p6drain electrode, PMOS M _p7grid be connected;

NMOS tube M _n4drain electrode and PMOS M _p7drain electrode, PMOS M in the amplifier of the second level _p8grid, PMOS M _p9grid be connected;

NMOS tube M _n1source electrode, NMOS tube M _n2source electrode, NMOS tube M _n3source electrode, NMOS tube M _n4source electrode respectively ground connection;

Second level amplifying circuit comprises PMOS M _p8, PMOS M _p9with NMOS tube M _n5, NMOS tube M _n6;

PMOS M _p8grid and PMOS M _p9grid be connected, then with PMOS M _p7drain electrode and the first amplifier in NMOS tube M _n4drain electrode be connected;

PMOS M _p8drain electrode, NMOS tube M _n5drain electrode, NMOS tube M _n5grid, NMOS tube M in third level amplifier _n7grid be connected;

PMOS M _p8, PMOS M _p9source electrode be connected respectively to supply voltage V _dD;

PMOS M _p9drain electrode, NMOS tube M _n6drain electrode, PMOS M in third level amplifier _p10grid be connected;

NMOS tube M _n6grid and the first amplifier in PMOS M _p3drain electrode, PMOS M _p5drain electrode, NMOS tube M _n2drain electrode, NMOS tube M _n2grid, NMOS tube M _n3grid be connected;

NMOS tube M _n5, NMOS tube M _n6source electrode respectively ground connection;

Institute's third level amplifying circuit comprises PMOS MP ₁₀with NMOS tube M _n7;

PMOS M _p10source electrode be connected to supply voltage V _dD;

PMOS M _p10grid and second level amplifier in PMOS M _p9drain electrode, NMOS tube M _n6drain electrode be connected;

PMOS M _p10drain electrode and NMOS tube M _n7drain electrode, the building-out capacitor Cc other end be connected and be linked into the output V of operational amplifier _oUT.

Further the frequency response of operational amplifier and transient response characteristic are verified below.Operational amplifier is verified under a kind of mixed signal 0.18 μm of CMOS technology, and the threshold voltage of NMOS tube and PMOS is 0.5V.

A kind of the result of the operational amplifier frequency response for medical electronics as shown in Figure 3.Wherein, operational amplifier positive input V _iN+ be 0.5V, operational amplifier negative input V _iN-connect output V _oUT, supply voltage V _dDfor 1.4V, load capacitance is 4nF, and operational amplifier quiescent current is 17 μ A.According to the result, op-amp gain is 110dB, and gain bandwidth product is 1.5MHz, and phase margin is 60 °.

A kind of the result of the operational amplifier transient response for medical electronics as shown in Figure 4.Wherein operational amplifier positive input V _iN+ switch between 0.2V and 0.7V, operational amplifier negative input V _iN-connect output V _oUT, supply voltage V _dDfor 1.4V, load capacitance is 4nF, and operational amplifier quiescent current is 17 μ A.According to the result, the settling time of operational amplifier is 1.5 μ s.

Although be described the illustrative embodiment of the present invention above; so that those skilled in the art understand the present invention; but should be clear; the invention is not restricted to the scope of embodiment; to those skilled in the art; as long as various change to limit and in the spirit and scope of the present invention determined, these changes are apparent, and all innovation and creation utilizing the present invention to conceive are all at the row of protection in appended claim.

Claims (2)

1. the operational amplifier for medical electronics, comprise the biasing circuit, first order amplifying circuit, second level amplifying circuit and the third level amplifying circuit that connect successively, it is characterized in that, the first order to third level amplifying circuit connects a building-out capacitor Cc, this building-out capacitor Cc one end concatenation operation amplifier out, the other end is connected to the efferent duct grid of first order amplifying circuit.

2. operational amplifier according to claim 1, is characterized in that, described biasing circuit comprises: PMOS M _p11with outside constant-current bias source I _b;

PMOS M _p11source electrode connect supply voltage V _dD, PMOS M _p11grid be connected to outside constant-current bias source IB, PMOS M _p11grid, drain electrode and PMOS M _p2grid be all connected, for generating the constant bias voltage V of PMOS _bP;

Described first order amplifying circuit comprises: PMOS M _p1, PMOS M _p2, PMOS M _p3, PMOS M _p4, PMOS M _p5, PMOS M _p6, PMOS M _p7, NMOS tube M _n1, NMOS tube M _n2, NMOS tube M _n3, NMOS tube M _n4with the first building-out capacitor Cc;

PMOS M _p1, PMOS M _p2, PMOS M _p3, PMOS M _p6, PMOS M _p7source electrode connect supply voltage V respectively _dD;

PMOS M _p1grid, PMOS M _p2grid, PMOS M _p3grid be connected with outside constant bias voltage source IB;

PMOS M _p1drain electrode, PMOS M _p4source electrode, PMOS M _p5source electrode is connected;

PMOS M _p2drain electrode, PMOS M _p4drain electrode, NMOS tube M _n1drain electrode, NMOS tube M _n1grid, NMOS tube M _n4grid be connected with building-out capacitor Cc one end;

PMOS M _p3drain electrode, PMOS M _p5drain electrode, NMOS tube M _n2drain electrode, NMOS tube M _n2grid, NMOS tube M _n3grid, and NMOS tube M in the second amplifier _n6grid be connected;

NMOS tube M _n3drain electrode and PMOS M _p6grid, PMOS M _p6drain electrode, PMOS M _p7grid be connected;

NMOS tube M _n4drain electrode and PMOS M _p7drain electrode, PMOS M in the amplifier of the second level _p8grid, PMOS M _p9grid be connected;

NMOS tube M _n1source electrode, NMOS tube M _n2source electrode, NMOS tube M _n3source electrode, NMOS tube M _n4source electrode respectively ground connection;

Described second level amplifier comprises PMOS M _p8, PMOS M _p9with NMOS tube M _n5, NMOS tube M _n6;

PMOS M _p8grid and PMOS M _p9grid be connected, then with PMOS M _p7drain electrode and the first amplifier in NMOS tube M _n4drain electrode be connected;

PMOS M _p8drain electrode, NMOS tube M _n5drain electrode, NMOS tube M _n5grid, NMOS tube M in third level amplifier _n7grid be connected;

PMOS M _p8, PMOS M _p9source electrode be connected respectively to supply voltage V _dD;

PMOS M _p9drain electrode, NMOS tube M _n6drain electrode, PMOS M in third level amplifier _p10grid be connected;

NMOS tube M _n6grid and the first amplifier in PMOS M _p3drain electrode, PMOS M _p5drain electrode, NMOS tube M _n2drain electrode, NMOS tube M _n2grid, NMOS tube M _n3grid be connected;

NMOS tube M _n5, NMOS tube M _n6source electrode respectively ground connection;

Described third level amplifier comprises PMOS MP ₁₀with NMOS tube M _n7;

PMOS M _p10source electrode be connected to supply voltage V _dD;

PMOS M _p10grid and second level amplifier in PMOS M _p9drain electrode, NMOS tube M _n6drain electrode be connected;

PMOS M _p10drain electrode and NMOS tube M _n7drain electrode, the first building-out capacitor Cc other end be connected and be linked into the output V of operational amplifier _oUT.