Summary

The theory that the article introduced to input voltaic noise to amplifier of operation of wave of a kind of behead is analysed and measure, this amplifier has 10 PF to input bandwidth of gain of PSD of noise of voltage of capacitance, 5.6 NV/√Hz and 4 MHz unit. When the closed circuit gain that should configure is taller, noise of input electric current in order to input behead wave implement the thermal noise that is in dynamic conductance is given priority to. In addition, the another origin — that theoretical analysis decided noise of input electric current by input behead wave implement the place of amplifier voltage noise that manages dynamic conductance sampling is caused. And, when sampling, spectrum density of broadband voltage noise can be folded return low frequency, make corresponding voltaic noise spectrum density takes wide broaden as closed circuit actually and increase, the closed circuit gain that configures consequently is smaller, voltaic noise spectrum density is bigger. It is when closed circuit gain 10 when, measures electric current noise is 0.28pA/√Hz, but when unit gain is configured, voltaic noise increases 0.77 PA/√Hz.

 

I. Foreword

Behead wave technology the maladjusted voltage of periodic corrective amplifier, reason can achieve level of small bend over maladjusted voltage and very little 1/f noise (its turn frequency under inferior hertz) 1, 2. Accordingly, amplifier of a lot of behead wave operation and appearance amplifier basically are used at detecting the small input voltage with source impedance and signal relatively inferior frequency. Its are important the signal of millivolt class sensor that one of application are enlarge report light, temperature, magnetic field, force, the frequency of this kind of signal thises under kilohertz mostly 2 however, compare at doing not have the traditional CMOS amplifier of behead wave, input behead wave implement switch can introduce get much input high to slant buy electric current and noise of input electric current 3, 4. The input when amplifier by Gao Yuan when impedance drive, noise of electric current of this kind of input can be changed to be voltage noise, its hold dominant position possibly in amplifier whole noise 3, 4.

 

Article“All sorts of possibilities that the measurement that voltaic noise inputs in behead wave amplifier and analytic ”4 explained noise of input electric current origin, and the charge with input MOS switch infuse comes loose relevantly bead noise is main noise source certainly. However, the ”5 of additional electricity noise in the amplifier that article “ takes switch to input will input behead wave implement the thermal noise of the dynamic conductance of place is main noise source certainly. In foregoing all measurement, the feedback attenuation that the output voltage noise of amplifier outputs an input through amplifier and input behead wave implement segregation.

 

Although be used at configuration of gain of tall closed circuit on tradition of amplifier of behead wave operation, but gain of low closed circuit and / or configuration of Gao Yuan impedance also needs his low maladjusted voltage and character of low 1/f noise 2. Accordingly, the voltaic noise action in understanding its to be configured in these is very significant. This article introduced simply to be mixed high low the noise of input electric current of amplifier of operation of wave of the behead below configuration of gain of two kinds of closed circuit is analysed and measure, the amplifier of operation of wave of 5.6 NV/√Hz behead that refers to “ to use technology of the Zhong Zengjiang when suiting oneself inputs the implementation inside limits to course in course the biggest 0.5μV is maladjusted ”6. It decided another origin that inputs voltaic noise, namely by input behead wave implement the place of noise of voltage of operation amplifier broadband of dynamic conductance sampling is caused. In addition, when sampling, come from behead wave occasionally second the voltage noise power spectral density of overtone frequency (PSD) can be folded return low frequency, bring about corresponding voltaic noise PSD to increase. Accordingly, when closed circuit gain is inferior, this noise source takes dominant place possibly in always inputting voltaic noise, make the output voltage noise of operation amplifier inputs behead wave with arriving lesserly damply implement.

 

The source of noise of input electric current that II part reviewed previous report, III part explained by sampling broadband voltage noise is mixed the inputs voltaic noise source mechanism that effect of relevant noise chart fold causes. All sorts of voltaic noise sources to operation amplifier had share of I V a few numerical value are calculated 6. The voltaic noise that V share gives consideration and emulate and measure a result to undertake comparative, with analysis of test and verify. VI part put forward to input a few proposals of voltaic noise about reducing, the article gave out in VII part finally a few conclusion.

 

II. The source of noise of input electric current of previous report

The measurement that voltaic noise inputs in amplifier of “ behead wave and analytic ” explained sources of following noise of 3 kinds of electric current in article. The first, the channel charge infuse that inputs switch can be Iq_ave of average electric current approximately, bring about thereby medicinal powder bead noise:

 

 

Among them FCHOPP is behead wave frequency, and (WLCox)SW and (VGS–The capacitance of grid oxidation layer that VTH)SW is switch respectively and voltage living drive.

 

The 2nd, clock driver generates KTCC noise charge, its are gone to by sampling on the capacitance of grid oxidation layer of switch, next noise charge inputs in what amplifier flows into when behead wave every time:

 

 

Graph 1. Behead wave and the trends that input capacitance to cause input electric current.

 

The 3rd, if the graph is shown 1 times, input behead wave every time implement when CHOP1 switch, IIN(t) of dynamic input electric current can flow into the input capacitance CIN of amplifier. Should bring to bear on when VIN(t) = VIN_DC of volts d.c. source, IIN_ave of average input electric current gives out by next type:

 

 

Next, GIN_ave of relevant dynamic input conductance and thermal noise In_GIN give out by next type:

 

 

Attention, 3 noise are equational 1, 2, 5 medium any include a group of distinctive circuit and switch parameter, differ according to joining numerical value, a kind of any noise take dominant place possibly in integral noise. In 3 all metrical amplifier (amplifier of appearance of wave of behead of an open loop and amplifier of operation of two behead wave, closed circuit gain is 100) , equation shows 1 times medicinal powder bead noise all takes dominant place in noise of total electric current 4. Amplifier of appearance of this open loop is only 125 FF inputs capacitance, because this is equational,the thermal noise of 5 shown dynamic conductance nots matter.

 

In the ” of additional electricity noise in the amplifier that takes switch input in article “ , measured the behead wave that makes by schism FET implement, when the schism electric capacity that adds 10pF to 100pF, the thermal noise that equation shows 5 times takes dominant place in noise of total electric current. Ask an attention, voltaic noise increases along with capacitance value and increase.

 

III. The voltaic noise that sampling voltage noise and effect of noise chart fold cause

Like equation 5 are alluded, dynamic conductance itself can produce thermocurrent noise, and its sampling operation returns meeting general to input behead wave implement the voltage noise changeover that go up is voltaic noise.

 

Sampling communication inputs the trends that voltage causes to input electric current

The dynamic input electric current below dc input voltage by equation 3 give out. The consideration has communication sine one kind to differ cent to input voltage VIN(t) and frequency now 2×The circumstance of FCHOPP, if pursue,2 are shown. Can see, when CHOP of behead wave clock and CHOP_INV switch, VIN(t) achieves VIN_AC of its peak value. Accordingly, like inputting voltage with respect to poor like dc cent, this communication differs cent to input voltage to produce trends to input voltaic IIN(t) , its are average voltaic IIN_ave gives out by next type:

 

Graph 2. The trends that communicates poor cent to input voltage to fall inputs voltaic weaveform.

 

Graph 3. Voltage noise PSD is changed to be the effect of noise chart fold when voltaic noise PSD by sampling

 

Should inputting the phasic difference between voltage and behead wave clock is random moment, equation can use the virtual value that inputs voltage VIN_RMS and IIN_ave_RMS of corresponding input electric current to rescript:

 

 

When with taller behead wave occasionally second overtone frequency (for example 4×FCHOP or 6×FCHOP) brings to bear on when communication inputs the voltage that need branch, input electric current also can appear with same way.

 

The PSD of noise of input electric current that PSD of sampling voltage noise and effect of noise chart fold cause

Include behead wave when the spectrum that inputs voltage many occasionally second when overtone frequency, they are folded entirely return low frequency, this is called effect of noise chart fold 1. Behead wave is considered as technology of a kind of modulation, is not sampling technology. However, input voltage and appear what this dynamic input electric current is based on sampling, either be based on successive input voltage and appear, because this meeting produces noise chart fold. In other words, the poor cent that flow of average and dynamic cable issues by behead wave circumstance only inputs voltage to decide, is not by the input needing branch of any other time voltage is decided.

 

Graph 3 showed effect of noise chart fold, input voltage noise PSD to arrive in DC among them 5×Enn is between FCHOP, but in 5×FCHOPP above is 0. This produced DC to arrive ±fCHOP (namely Nai Kui this special frequency) the PSD of noise of input electric current between. The PSDen(fen) of input voltage noise between ±fCHOP can contribute the PSDin_en_GIN_0 of noise of input electric current that moves without frequency.

 

 

W among them, fen and Fin are an input respectively the frequency of voltage noise PSD and PSD of corresponding noise of input electric current. Prep above FCHOP and under 3×The PSD of input voltage noise of FCHOP can contribute frequency to move for –2×The PSD of noise of input electric current of FCHOP:

 

 

PSDin_en_GIN_RSS(f) of noise of total input electric current is to pass pair of operation amplifier to shut the PSD of all frequency folding inside annulus bandwidth to undertake sue for peace gets, include equation 8 with those 9 medium PSD, use and root (RSS) computation:

 

 

Be evenness is in in En when voltage noise PSD, and take be restricted frequency is Fen_BW, PSD of corresponding noise of low frequency electric current gives out by next type:

 

 

When Fen_BW/fCHOP >>1 when, equation can be approximately:

 

Among them, en×√fen_BW is replaced by En_RMSINT of noise of voltage of integral virtual value. The square root of size of capacitance of the noise of virtual value voltage that source of noise of this input electric current carries with the input that need branch roughly, input and behead wave frequency becomes scale.

 

The noise of input electric current of amplifier of behead wave operation estimates

Block diagram of amplifier of behead wave operation

The amplifier of this part and the partial analysis from the back, operation of wave of behead of 5.6 NV/√H Z that emulate and measures “ to use technology of the Zhong Zengjiang when suiting oneself inputs the implementation inside limits to course in course the biggest 0.5µThe amplifier of behead wave operation that V introduces in maladjusted ” . This operation amplifier uses implementation of 0.35μm CMOS craft, complementary with 5 V transistor, realized the unit gain bandwidth of the voltage noise PSD of 5.6 NV/√Hz and 4 MHz. Its block diagram is shown 4 times like the graph, express 1 summary input behead wave implement (the parameter of CHOP1) . Input to course to achieve orbit in all modular limits, the input is crossed guide amplifier class Gm11 divides pair of composition by N raceway groove and difference of P raceway groove, both can contribute input capacitance CIN. Need the input MOS parts of an apparatus of larger size in addition, compare those who increase Gm1 to cross with tall effect thereby guide. Input behead wave implement there are 4 switches in CHOP1, every switch is come true by NMOS, and its grid voltage is based on input voltage and suit oneself slant buy, make when inputting voltage to change, its cross drive voltage constant in 0.5 V.

 

Graph 4. Block diagram of amplifier of behead wave operation

 

Express 1. Input behead wave implement (the parameter of CHOP1)

 

The input that need branch carries the voltage noise on

For computational equation 12 in shows voltaic noise PSD, need knows Vin_RMSINT of noise of voltage of integral virtual value. =1 of gain of use closed circuit, 2, 5, amplifier of operation of wave of 10 emulation behead. Graph 5(a) and (the voltage noise PSD that B) showed to operation amplifier differs minute of input to carry respectively and noise of its integral virtual value. All emulation in the article all emulate by SpectreRF periodic noise (PNOISE) undertakes, in order to consider the switch effect of behead wave 7. As a result of behead wave, noise PSD is even under 100 KHz, but peak value is reached in the place of behead wave frequency of 200 KHz 6. Ask an attention, these numbers state operation amplifier differs cent to input the noise of end, is not to output upright noise, because this is under the noise PSD of 100kHz below gain of different closed circuit,be constant. In 1MHz above, noise PSD also can increase, and with Gm2, gm3, give priority to with the thermal noise of Gm4, the gain that the reason is Gm1 drops. Accordingly, noise of its integral virtual value also can increase in 1 MHz above, fall in the circumstance with closed circuit inferior gain especially, main reason is closed circuit bandwidth taller. When gain = 10, the noise of voltage of integral virtual value that the input that need branch carries is 11 μVrms, but 68 μVrms is when gain = 1.

 

Graph 5. The emulation difference of amplifier of behead wave operation divides input voltage noise

 

Every input the estimation of voltaic noise source

Will emulate noise of gotten voltage of integral virtual value to apply at equation next 12 with PSD of noise of computational electric current. Additional, other noise source the 4 voltaic noise PSD that cause are through will be being expressed 1 medium parameter applies at equation 1, 2, 5 come calculative. Graph 6 showed closed circuit gain the voltaic noise PSD from the 1 4 noise source to 10 chronometer cipher out. It is when closed circuit gain 1 and 2 when, the voltaic noise PSD that PSD of noise of sampling broadband voltage causes (equational 12) dominant place is taken in PSD of noise of total electric current. It rises as closed circuit gain and reduce, it is when closed circuit gain 10 when, its make always input voltaic noise PSD to increase only 7% . Contrary, when prep above of closed circuit gain 5 when, PSD of noise of total electric current the thermal noise with dynamic conductance itself (equational 5) give priority to, keep constant almost so. Accordingly, to this operation amplifier, use 10 times more highest closed circuit gain will evaluate voltaic noise namely enough 6

 

V. Emulate and measure an outcome

For analysis of test and verify, the figure PSD of 6 shown noise of total electric current are calculated result and emulate and measure a result to undertake comparative. PNOISE is emulated and measure all use a figure 7 show circuit setting to undertake. Voltage noise PSDen_OUT is to pass short circuit RS to measure, total noise PSDen_OUT_RS is undertake metrical below RS = 100 KΩ . Voltaic noise PSD In_IN gives out by next type:
 

 

Among them, (1 + RF/RG) is the closed circuit gain all round operation amplifier, GPOST =100 is postposition gain, in order to simplifies the measurement of HP 35670A of dynamic signal analyzer. The attention is in equational 13 in, en_OUT_RS and En_OUT subtract with RSS form, because voltaic noise PSD is main by relatively high-frequency fold noise is caused, consequently with voltage noise PSD not relevant.

 

Graph 6. The noise of input electric current of different origin contributes computational result

 

 

Graph 7. Use at inputting the circuit setting that voltaic noise is emulated and measures

 

Exterior capacitance CS = 100 PF is in the noise bandwidth limitation of RS end frequency 16 KHz. Below this kind of circumstance, the thermal noise of RS is in of behead wave the first occasionally second overtone frequency (400kHz) place gets sufficient attenuation, because this won’t pass noise of electric current of contribution of effect of noise chart fold. On the other hand, operation amplifier broadband outputs voltage noise to achieve negative input VINN, , by input behead wave implement the dynamic conductance sampling of place, may contribute noise of electric current of quite a few. Subsequently, the voltaic noise PSD in low frequency is changed to be voltage noise by RS again, this noise can be in the output end of postposition gain level undertakes metrical.

 

Graph 8 showed gain = 1 is configured (RG open a way and RF short circuit, if the graph is shown 7 times) next emulation and measure gotten complete frequency range to input voltaic noise PSD. When 0.01 KHz, emulate and measure gotten noise PSD to be 0.69 PA/√Hz and 0.78 PA/√Hz respectively. Next, noise PSD ends in the 16 KHz that arises by RS and CS frequency place begins to drop. Graph the PSD of 9 noise of input electric current when showing gain of different closed circuit issues 0.01 KHz, with will pursueing 6 medium computation are worth with emulate and measure a result to undertake comparative. Emulate and measure gotten voltaic noise PSD to reduce and all increase of gain as closed circuit, with computation the result has good dependency. The PSD of noise of input electric current that measures when gain =10 is 0.28 PA/√Hz, but the biggest 0.77 PA/√Hz rises when gain = 1.

 

Graph 8. Input the relation of voltaic noise PSD and frequency

 

Graph 9. The inputs voltaic noise PSD and closed circuit gain relation when 10 Hz

 

VI. Reduce the proposal that inputs voltaic noise

Equational 1, 2, 5, the sources of 12 noise of all electric current that give out increase into scale with the square root of behead wave frequency. In addition, with input behead wave implement the voltaic noise source related place trends conductance (equational 5 and 12) capacitance increases and increase as the input of amplifier. The amplifier of behead wave operation that this means in the light of PSD of inferior voltage noise design often has PSD of taller noise of input electric current, because need increases his,input the size of parts of an apparatus. In give source impedance to fall, must understand ability of this kind of balance to realize optimal voltage noise and voltaic noise PSD. If likelihood, should avoid to be in invert to complementary input is used to be opposite below the area or input transistor infirmly, so that reduce input electric capacity.

 

Equational 12 make clear, voltaic noise PSD divides the integral virtual value on the input to voltage noise increases and increase as amplifier difference, can increase as noise bandwidth consequently and increase. Compare with amplifier of appearance of wave of open loop behead, amplifier of behead wave operation is planted more easily by this the influence of noise source, because its output noise,can reach input end through feedback network. If likelihood, can use gain of taller closed circuit to reduce noise bandwidth. Another kind of idea that drops noise bandwidth is capacitance and RG, RS and / or amplifier differs cent to input paralell connection, if pursue,7 are shown.

 

VII. Conclusion

The article determined cause of noise of electric current of another kind of input, it is by input behead wave implement the place of noise of amplifier broadband voltage that manages dynamic conductance sampling causes. The article returns discovery, differ with the other noise source that tells before, PSD of noise of this electric current takes wide broaden as closed circuit and increase, the reason depends on with input behead wave implement effect of relevant noise chart fold. Measure the analysis that confirmed the article as a result: When gain =10, voltaic noise is 0.28pA/√Hz; When gain =1, because shut annulus bandwidth to increase, voltaic noise raises 0.77pA/√Hz. The article designed personnel and user to offer a few proposals that input voltaic noise about reducing behead wave amplifier for amplifier. Express the amplifier of 2 behead wave operation that compared the article to evaluate 6 with its he has PSD of similar voltage noise recently amplifier of behead wave operation 8, 9, the integral function of 10.

 

Express 2. The norms of amplifier of behead wave operation