CN101521496A - Low-gain switching capacitor in-phase integrator with insensitive parasitic effect and low power consumption - Google Patents

Abstract

The invention discloses a low-gain switching capacitor in-phase integrator with low power consumption, which comprises an operational amplifier, an integral capacitor and a sampling capacitor, wherein the first end of the sampling capacitor is respectively connected with a switch which switches on the input voltage at the sampling phase position and a switch which switches on the common mode voltage at the second input end of the operational amplifier at the integral phase position, and the second end of the sampling capacitor is connected with the first input end of the operational amplifier through the switch which switches on at the integral phase position; the first end of a fourth capacitor is respectively connected with the switch which switches on the input voltage at the sampling phase position and a switch which switches on the input signal common mode voltage at the integral phase position, and the second end of the fourth capacitor is respectively connected with a switch which switches on the sampling capacitor at the sampling phase position and the switch which switches on the input signal common mode voltage at the integral phase position; the first end of a third capacitor is connected with the second end of the fourth capacitor, and the second end of the third capacitor is connected with the input signal common mode voltage. The integrator has low gain coefficient and is insensitive to the parasitic effect of the capacitor, thereby reducing the load capacitance of the operational amplifier and the power consumption of the integrator.

Description

Ghost effect is insensitive, the little gain switch electric capacity noninverting integrator of low-power consumption

Technical field

The present invention relates to the switched-capacitor circuit technical field, relate in particular to that a kind of ghost effect is insensitive, the little gain switch electric capacity noninverting integrator of low-power consumption.

Background technology

Switched-capacitor integrator is widely used in the various electronic signal process system, as filter, data converter and sensor network etc.Under certain integrated circuit processing technique condition, the electric capacity value is restricted, and is approximately 0.1pF as the capacitance that can accurately realize under 0.35um technology, and this has just largely limited the realization of little gain coefficient switched-capacitor integrator.Yet in some application scenarios, need use the switched-capacitor integrator of little gain, such as Sigma-Delta data converter feedback factor with optimize zero point such as coefficient etc.The conventional switch capacitance integrator generally can be realized the gain coefficient greater than 1/20, if will realize gain coefficient and one timing of integrating capacitor value less than 1/20, so just to realize accurately little gain coefficient with accurate little capacitance.Unless, in keeping integrator, under the constant condition of sampling capacitance value, increases the integrating capacitor value and could realize little gain coefficient, but this just brings shortcoming of circuit area increase.In addition, in order to reduce the switched-capacitor integrator power consumption, corresponding low power design technique has been adopted in the design of integrator, and as switched OPAMP technology, this technology only needs operational amplifier in the integrate phase operate as normal.Switched-capacitor integrator disclosed by the invention not only can be realized gain of small scale coefficient and big time constant, and it is insensitive to the electric capacity ghost effect, and has optimized the integrator circuit area and be applicable to the low-power consumption field.

Conventional switch capacitance integrator circuit comprises: an operational amplifier, two electric capacity and four switches.A work period of circuit comprises two non-overlapping clock phase places: sampling phase φ ₁, integrate phase φ ₂, as shown in Figure 1.Conventional switch capacitance integrator circuit as shown in Figure 2.C ₁Be sampling capacitance, C ₂Be integrating capacitor, V _CMBe the input signal common-mode voltage, INCM is the operational amplifier common mode input, V _INBe input voltage, V _OUTBe output voltage, Op-amp is an operational amplifier, and T is the sampling clock cycle, and fs is the sampling clock frequency.

The course of work of conventional switch capacitance integrator is as follows:

1. at sampling phase φ ₁The time, input voltage V _INBy capacitor C ₁Sampling.At sampling phase φ ₁During end, C ₁On storing certain electric charge.

2. at integrate phase φ ₂The time, the sampled signal on the sampling capacitance is delivered to integrating capacitor C by operational amplifier ₂On.

Analyze by the z domain model, the transfer function of conventional switch capacitance integrator is:

$\frac{V_{\mathrm{OUT}}}{V_{\mathrm{IN}}}=\frac{c_1}{c_2}\frac{z^{-\frac{1}{2}}}{1-z^{-1}}$

And then the time constant of conventional switch capacitance integrator is:

$\mathrm{\&tau;}=\frac{c_2}{{\mathrm{<figure-callout\; id="1"\; label="c"\; filenames="A200910097673E00091.png,A200910097673E00102.png"\; state="\{\{state\}\}">c</figure-callout>}}_1}\frac{1}{f_s}$

The gain that can get the conventional switch capacitance integrator according to transfer function is the ratio C of two electric capacity ₁/ C ₂The minimum capacity value is 0.1pF under 0.35um technology, capacitor C ₂Value is 2pF, and the least gain value of conventional switch capacitance integrator can only be accurate to about 1/20 so.If realizing gain coefficient is the integrator below 1/40, that can only be by increasing integrating capacitor C ₂To 4pF with on realize that the total capacitance that this moment, integrator adopted is more than the 4.1pF, circuit area, power consumption obviously increase.Yet, in some application scenario, such as adder, Sigma-Delta data converter etc., integrating capacitor C ₂Can not arbitrarily increase, so traditional switched-capacitor integrator just can not be realized little gain coefficient, therefore just this drawbacks limit its application.

Shortcoming in view of the conventional switch capacitance integrator, in the prior art as " AParasitic-Insensitive Area-Efficient Approach to Realizing Very Large TimeConstants in Switched-Capacitor Circuits " (" IEEE TRANSACTIONS ONCIRCUITS AND SYSTEMS " P 1210-1216 of K.NAGARAJ, VOL.36, NO.9, SEPTEMBER1989) introduced a kind of improved switching capacity noninverting integrator in, it is compared with traditional switched-capacitor integrator has increased an extra capacitor C ₃, physical circuit as shown in Figure 3.The course of work of the switched-capacitor integrator after the improvement is as follows:

1. in phase ₁The time, electric charge C ₁V _INBe delivered to integrating capacitor C by operational amplifier ₂On.The while capacitor C ₃Will be at the output voltage signal V of the last end of term in week sampling preservation _OUT(n-1) with integrating capacitor C ₂Again distribute.

2. in phase ₂The time, capacitor C ₁By operational amplifier from integrating capacitor C ₂Last absorption electric charge.The while capacitor C ₃Output voltage signal V is preserved in sampling _OUT(n), prepare for next cycle conversion.

Analyze by the z domain model, the transfer function of improvement switching capacity noninverting integrator of the prior art is:

$\frac{V_{\mathrm{OUT}}}{V_{\mathrm{IN}}}=\frac{c_1{c}_3}{c_2({\mathrm{<figure-callout\; id="2"\; label="c"\; filenames="A200910097673E00091.png,A200910097673E00102.png"\; state="\{\{state\}\}">c</figure-callout>}}_2+c_3)}\frac{z^{-\frac{1}{2}}}{1-z^{-1}}$

And then the time constant of improvement switching capacity noninverting integrator of the prior art is:

$\mathrm{\&tau;}=\frac{c_2({\mathrm{<figure-callout\; id="2"\; label="c"\; filenames="A200910097673E00091.png,A200910097673E00102.png"\; state="\{\{state\}\}">c</figure-callout>}}_2+c_3)}{c_1{c}_3}\frac{1}{f_s}$

The gain that can get improvement switching capacity noninverting integrator of the prior art according to above-mentioned transfer function is C ₁C ₃/ C ₂(C ₂+ C ₃).The minimum capacity value is 0.1pF under 0.35um technology equally, capacitor C ₂Value is 2pF, and the least gain value of this switched-capacitor integrator can be accurate to about 1/420 so.At this moment, C ₁And C ₃Value all is 0.1pF, and the total capacitance that integrator adopts is 2.2pF.Yet, in some application scenario, allow operational amplifier only be operated in half period in order to reduce the integrator power consumption, half period is closed operational amplifier in addition.But improvement switching capacity noninverting integrator of the prior art needs operate as normal all of whole cycle of operational amplifier.This technology is also mentioned the switched-capacitor integrator of T type network, and it can realize the switched-capacitor integrator of little gain, and only needs operational amplifier operate as normal half period, but T type network switching capacitance integrator is relatively more responsive to the electric capacity ghost effect.

Summary of the invention

The invention discloses that a kind of ghost effect is insensitive, the little gain switch electric capacity noninverting integrator of low-power consumption.

A kind of ghost effect is insensitive, the little gain switch electric capacity noninverting integrator of low-power consumption, comprising:

The operational amplifier that has first input end, second input and output;

The integrating capacitor C that two ends link to each other with output with the first input end of operational amplifier respectively ₂

The sampling capacitance C that links to each other with the first input end of operational amplifier ₁

Described sampling capacitance C ₁First end be connected to respectively at sampling phase and connect input voltage V _INFirst switch and connect the second switch of the operational amplifier second input common-mode voltage INCM, sampling capacitance C in integrate phase ₁The three switch concatenation operation amplifier first input end of second end by connecting in integrate phase;

Be provided with the 4th capacitor C ₄, the 4th capacitor C ₄First end be connected to respectively at sampling phase and connect input voltage V _INThe 4th switch and connect input signal common-mode voltage V in integrate phase _CMThe 5th switch, the 4th capacitor C ₄Second end be connected to respectively at sampling phase and connect sampling capacitance C ₁Second end the 6th switch and connect input signal common-mode voltage V in integrate phase _CMMinion close;

Be provided with the 3rd capacitor C ₃, the 3rd capacitor C ₃First end connect the 4th capacitor C ₄Second end, the 3rd capacitor C ₃Second end connect input signal common-mode voltage V _CM

Input signal common-mode voltage V _CMDescribed in input signal refer to input voltage V _INThe input signal at place.

The invention discloses that a kind of ghost effect is insensitive, the little gain switch electric capacity noninverting integrator of low-power consumption.This little gain switch electric capacity noninverting integrator circuit comprises: an operational amplifier Op-amp, four electric capacity and seven switches.A work period of circuit comprises two non-overlapped phase places: sampling phase φ ₁With integrate phase φ ₂In circuit, additionally introduce two capacitor C ₃And C ₄, make switched-capacitor integrator can realize little gain coefficient, obtain big time constant.

The realization of this circuit function only needs the operational amplifier operate as normal at integrate phase φ ₂The needed non-overlapped phase clock of integrator as shown in Figure 1.

Whole switched-capacitor integrator circuit as shown in Figure 4, the dotted line switch of operational amplifier link represents to allow operational amplifier only need operate as normal at integrate phase φ ₂

This switched-capacitor integrator circuit with respect to the advantage of conventional switch capacitance integrator is: because two electric capacity of extra introducing, make switched-capacitor integrator can realize little gain coefficient, and under certain integrated circuit processing technique and little gain coefficient condition, this circuit has been realized circuit area optimization well.Simultaneously, owing to do not have unsettled node in the circuit, this switched-capacitor integrator is insensitive to the electric capacity ghost effect.And circuit only needs the operational amplifier operate as normal at integrate phase φ ₂, so the power consumption of integrator obviously reduces.Circuit of the present invention is that a kind of ghost effect is insensitive, the little gain switch electric capacity noninverting integrator of low-power consumption.

Description of drawings

Fig. 1 is a switched-capacitor integrator circuit working cycle schematic diagram in the prior art, has shown the non-overlapping clock phase place among the figure, wherein sampling phase (φ ₁), integrate phase (φ ₂);

The circuit diagram of the switched-capacitor integrator that Fig. 2 is traditional;

The circuit diagram of Fig. 3 improvement switching capacity of the prior art noninverting integrator;

Fig. 4 is insensitive for ghost effect of the present invention, the circuit diagram of the little gain switch electric capacity noninverting integrator of low-power consumption.

Embodiment

Ghost effect of the present invention is insensitive, the little gain switch electric capacity noninverting integrator course of work of low-power consumption is as follows:

1. at sampling phase φ ₁The time, first switch, the 4th switch and the 6th switch connection, input voltage V _INBe sampled capacitor C ₁, the 3rd capacitor C ₃And the 4th capacitor C ₄The capacitance network sampling of forming.At sampling phase φ ₁During end, sampling capacitance C ₁, the 3rd capacitor C ₃And the 4th capacitor C ₄On all storing certain electric charge.

2. at integrate phase φ ₂The time, second switch, the 3rd switch.The 5th switch and minion are closed and are connected the 3rd capacitor C ₃And the 4th capacitor C ₄Two ends are connected to common-mode voltage, and electric charge is cleared on it.Sampling capacitance C ₁On electric charge be delivered to integrating capacitor C by operational amplifier ₂On.The process that exists twice gain to dwindle at first is that input signal is sampled capacitor C like this ₁, the 3rd capacitor C ₃And the 4th capacitor C ₄Distribute, realized gaining and dwindled for the first time; Then in integrate phase only to sampling capacitance C ₁On charge transfer to integrating capacitor C ₂On, realized gaining and dwindled for the second time.

Analyze by the z domain model, ghost effect is insensitive, the transfer function of the little gain switch electric capacity noninverting integrator of low-power consumption is:

$\frac{V_{\mathrm{OUT}}}{V_{\mathrm{IN}}}=\frac{c_1{c}_3}{c_2({\mathrm{<figure-callout\; id="1"\; label="c"\; filenames="A200910097673E00091.png,A200910097673E00102.png"\; state="\{\{state\}\}">c</figure-callout>}}_1+c_3+c_4)}\frac{z^{-\frac{1}{2}}}{1-z^{-1}}$

And then ghost effect is insensitive, the little gain switch electric capacity noninverting integrator time constant of low-power consumption is:

$\mathrm{\&tau;}=\frac{c_2({\mathrm{<figure-callout\; id="1"\; label="c"\; filenames="A200910097673E00091.png,A200910097673E00102.png"\; state="\{\{state\}\}">c</figure-callout>}}_1+c_3+c_4)}{c_1{c}_3}\frac{1}{f_s}$

According to above-mentioned transfer function, the gain of this little gain switch capacitance integrator is a ratio C ₁C ₃/ (C ₂(C ₁+ C ₃+ C ₄)).The minimum capacity value is 0.1pF under 0.35um technology equally, capacitor C ₂, C ₄Value is 2pF, and the least gain value of this switched-capacitor integrator can be accurate to about 1/140 so.At this moment, C ₁And C ₃Value all is 0.1pF, C ₂Value is 2pF, C ₄Value is 0.5pF, and the total capacitance that integrator adopts is 2.7pF.If this switched-capacitor integrator realizes that gain is at 1/440 o'clock, then C ₁And C ₃Value all is 0.1pF, C ₂And C ₄Value is 2p, and the total capacitance that integrator adopts is 4.2pF.Because the equivalent load capacitance of operational amplifier depends primarily on C ₁And C ₂, then when this integrator realized that gain coefficient is 1/440, the area of integrator can increase to some extent but power consumption does not increase.And this integrator circuit is at sampling phase φ ₁The time, close operational amplifier, only at integrate phase φ ₂Allow its work.Thereby reached the minimizing operational amplifier operating time, reduced the purpose of power consumption.

Ghost effect disclosed by the invention is insensitive, the little gain switch electric capacity noninverting integrator of low-power consumption Compare at circuit with traditional switched-capacitor integrator, increased by two extra electric capacity and three and opened Close, can realize that gain is the switched-capacitor integrator more than 1/140. The improvement of it and prior art is opened Close the electric capacity noninverting integrator and compare, increased by four switches and one 's electric capacity, circuit area increases to some extent Add. But circuit of the present invention but do not increase the pay(useful) load electric capacity of operational amplifier. And circuit only Need the operational amplifier normal operation at integrate phase φ₂, reduced the operational amplifier working time, from And reach the purpose that reduces circuit power consumption. Therefore, the present invention can break through the restriction of integrated circuit technology, Be specially adapted to the fields such as little gain coefficient and low-power consumption, enlarged the application of switched-capacitor integrator.

Claims (1)

1, the little gain switch electric capacity noninverting integrator of insensitive, the low-power consumption of a kind of ghost effect comprises:

The operational amplifier that has first input end, second input and output;

Integrating capacitor (the C that two ends link to each other with output with the first input end of operational amplifier respectively ₂);

Sampling capacitance (the C that links to each other with the first input end of operational amplifier ₁);

It is characterized in that: described sampling capacitance (C ₁) first end be connected to respectively at sampling phase and connect input voltage (V _IN) first switch and connect the second switch of the operational amplifier second input common-mode voltage (INCM), sampling capacitance (C in integrate phase ₁) the three switch concatenation operation amplifier first input end of second end by connecting in integrate phase;

Be provided with the 4th electric capacity (C ₄), the 4th electric capacity (C ₄) first end be connected to respectively at sampling phase and connect input voltage (V _IN) the 4th switch and connect input signal common-mode voltage (V in integrate phase _CM) the 5th switch, the 4th electric capacity (C ₄) second end be connected to respectively at sampling phase and connect sampling capacitance (C ₁) second end the 6th switch and connect input signal common-mode voltage (V in integrate phase _CM) minion close;

Be provided with the 3rd electric capacity (C ₃), the 3rd electric capacity (C ₃) first end connect the 4th electric capacity (C ₄) second end, the 3rd electric capacity (C ₃) second end connect input signal common-mode voltage (V _CM).

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