CN100521518C - Digital microphone - Google Patents
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- CN100521518C CN100521518C CNB2005800043951A CN200580004395A CN100521518C CN 100521518 C CN100521518 C CN 100521518C CN B2005800043951 A CNB2005800043951 A CN B2005800043951A CN 200580004395 A CN200580004395 A CN 200580004395A CN 100521518 C CN100521518 C CN 100521518C
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Abstract
An integrated circuit, configured to process microphone signals, where the integrated circuit comprises: a preamplifier (306) with an amplifier section (301) which has a first input ([phi]) and a second input ([phi]*) and an output (phi), and with a feedback filter network (Z1; Z1, Z1 *, Z2) coupled between the output (phi; phi, phi*) and the second input ([phi]'); where the first input ([phi]) to the amplifier section (301) has an input impedance which by means of the input impedance of the amplifier section is substantially isolated from the feedback network with respect to input impedance; and where the preamplifier has a frequency-gain transfer function which suppress low frequencies; and an analogue-to-digital converter coupled to receive an anti-aliasing filtered input signal and providing a digital output signal (Do).
Description
Technical field
The present invention relates to comprise microphone preamplifier and be used to provide the integrated circuit of the A-D converter of digital output signal.In addition, the invention still further relates to the digital microphone that comprises microphone unit and above-described integrated circuit.
Background technology
The acoustic pressure that microphone unit detected will make its motion of membrane, thereby change by its diaphragm and the electric capacity of the capacitor that forms of so-called microphone unit backboard.When the electric charge on the capacitor that is formed by these two members remained unchanged, the voltage between two members of capacitor just changed with the acoustic pressure that acts on the diaphragm.Because the electric charge on the microphone capacitor must remain unchanged to keep the proportionate relationship of the voltage between acoustic pressure and the capacitor component, importantly microphone electric capacity should not be added with resistive load.Resistive load will make the capacitor discharge, therefore worsen even destroy the performance as microphone of capacitor.
Therefore,, preferably dispose the amplifier that main purpose provides high input resistance, so that make capacitor and break away from for the optimized circuit of other purposes in order to pick up microphone signal from capacitor.Be connected the amplifier that picks up microphone signal and be commonly referred to preamplifier or buffer amplifier, perhaps abbreviate buffer as.Preamplifier is connected into physically very usually near capacitor, and distance has only several millimeters even less than 1 millimeter.
For small-sized microphone, effective capacitance is very little (being generally 1 to 10pF).This has further improved the requirement to high input resistance and electric capacity.Therefore, the input resistance of the preamplifier of small-sized microphone must be very high, be in the magnitude of begohm.In addition, the input capacitance of this amplifier must be very little, so that acoustic pressure is had goodish sensitivity.
Particularly, the so-called telecommunication microphone that has integrated preamplifier is sold with low-down price in a large number.Because the cost of the amplifier of telecommunication microphone is directly relevant with the size of preamplifier chip, therefore importantly make preamplifier chip as far as possible little in order to reduce price.Therefore, compact circuit is especially noticeable, and sort circuit has very big demand.Yet, importantly to provide noise level low circuit in this respect.Low noise is important, because noise can change area into, that is to say, ifs circuit has low noise, noise ratio is desired also low, and this noise level can be converted into less chip area so, thereby just can make preamplifier with lower cost.
When using the preamplifier of CMOS art designs microphone, consider three noise sources usually.These sources come the noise of self-bias resistor, from the 1/f noise of input transistors with from the white noise of input transistors.Suppose that the noise of input transistors preponderates.Can minimize white noise and 1/f noise by length and the width of optimizing input transistors.This is applicable to any input stage, for example single transistor stage or differential stage.Come the noise of self-bias resistor also can be minimized.If make biasing resistor very big, will carry out high-pass filtering to noise from this resistance, in-band noise is just very low like this.But this have make amplifier the low bandwidth limit with low-down influence.This may be a problem, because amplifier input terminal is only powering up back one section later for a long time nominal value that just is stabilized in.In addition, the signal with strong low-frequency content that causes owing to the infrasound of for example closing the door with strength or car is interior may make the amplifier overload.Another relevant issues are because chip is installed in the microphone module and can causes little leakage current.This electric current will be set up the DC biasing very greatly owing to input impedance.This will make the g tolerance of amplifier reduce.
Except above, also have comprising microphone unit and having preamplifier and the demand of the digital microphone of the integrated circuit of the A-D converter that digital output signal is provided.Because the telecommunication microphone is integrated into a large amount of Digital Signal Processing usually by mainly being the home electronics that digital integrated circuit chip is carried out, therefore usually preferably in the future the signal of autobiography sensor (such as microphone) provide as digital signal.This carries out having introduced new problem aspect the signal processing in being embedded with the integrated circuit of microphone, particularly aspect the distortion in numeric field.
In the last few years, the ∑ Delta modulator had been used for realizing the A/D converter already very at large.The ∑ Delta modulator has many advantages, does not particularly need high-precision assembly and highly linear; For so-called monocycle modulator, also has the advantage that chip area is little, operating voltage is low and power consumption may be very little.These advantages make the ∑ Delta modulator be very suitable for monolithic and realize.
The ∑ Delta modulator that a kind of special ∑ Delta modulator is 1 bit quantization.This modulator is particularly suitable for low-cost the realization, because this A/D converter is compared with the A/D converter of other types, the simulation part is the simplest.Whole 1 bit sigma Δ converter includes only one 1 bit analog sigma-delta modulator and a digital decimation filter.Usually required more high-order frequency overlapped-resistable filter can be realized with a simple RC filter.This is that therefore digital decimation filter is carried out the task of anti-aliasing filter owing to use very heavy over-sampling.
1 bit sigma Delta modulator is realized very simple at analog domain.Therefore, they are suitable for low-cost miniature digital microphone very much.Unfortunately, they also have some shortcomings really.Particularly, 1 bit sigma Delta modulator can present so-called empty mould sound (idle mode tone), and these sky mould sounds are the low level sounds in the voiced band that causes of low frequency on the input of modulator or DC level.Reason that 1 bit sigma Delta modulator given up by many people that Here it is is although it has many advantages.Can eliminate this problem with dither, perhaps design the Chaos Modulation device, but all these solutions all can make the complexity of design enlarge markedly.Therefore, power consumption still is that chip area all enlarges markedly.
This empty mould audio should make the ∑ Delta modulator not quite be fit to high-quality voice applications.Obviously, this may seem to use few of relation with family expenses/telecommunication.But,, also make performance bring up to the performance that almost can equal high quality audio with requiring along with the demand to the low-cost digital microphone increases.Therefore, empty mould audio is tackled in the telecommunication application also will become increasing problem.
In order to make digital microphone have high performance, the preamplifier of digital microphone ASIC must have high as far as possible performance, and promptly noise is low, distortion is little, dynamic range is big etc.According to current available technology, the CMOS technology is that the acquisition low-noise performance is necessary, can see that the input stage that can make amplifier is to the noise optimization.In addition, input impedance should be big as far as possible, so that minimum noise.This for new thinner have than the telecommunication microphone of the much lower sensitivity of former institute experience and pick-up head electric capacity outstanding especially.
Unfortunately, the result who makes like this be preamplifier with regard to amplifying because close the door with strength, automobile rumble or the low frequency signal that causes with the acoustic pressure of the change of humidity of the sensitivity of microphone unit just.If adopt 1 bit sigma Delta modulator, this has aggravated empty mould mail topic discussed above.In fact, 2 bits and have even more multistage modulator is done the time spent and also will be presented this behavior being subjected to this low frequency signal.
In addition, these low frequency signals have reduced dynamic range and have produced intermodulation distortion, because these low frequency signals can be excessive on amplitude.
Require the gain of preamplifier increasing along with the telecommunication microphone is more and more littler with more and more approaching therefore, the problems referred to above are more serious.Yet the low frequency signal of upsetting can't diminish on amplitude usually.Therefore, the relative effect of upset will increase.
Therefore, be necessary to develop preamplifier and the A/D converters that is suitable for the very low and thin ECM pick-up head that electric capacity is very little of sensitivity.In addition, this configuration should have very high performance in noise, dynamic range and distortion.And this configuration should be able to realize almost there is not external module on the very little single chip of area.
In the following description, used term " voiced band ".In the prior art, this term has different definition in different contexts.Yet, below it will to be used to refer to a usually low half-power frequency be 20 hertz to 500 hertz and high half-power frequency is 5 kilo hertzs to 25 kilo hertzs a frequency band.The concrete define and represent of this frequency band the criterion of design, but for following explanation, should define widely and understand with this.
Add behind the simple buffer amplifier that this so-called two-stage preamplifier configuration of filter has two shortcomings: because it has two-stage, noise is just bigger, and because not gain of the first order, the physical size of filter have to be bigger.The size of filter can minimize by the gain that increases the first order, but amplifier is very sensitive to the overload owing to low frequency component, and the filter that these low frequency components will arrive subsequently just can obtain reducing.Therefore, this was best for the solution of hearing aids microphone exploitation is far from for new highly sensitive telecommunication microphone originally.The area of amplifier chip only can be too big, so device is not economic.
Because the shared chip area of preamplifier must be as far as possible little, so that cost is lower, so preamplifier must be as far as possible little.Therefore, because the amplifier configuration of knowing from hearing aids is not optimized to the degree same with the telecommunication microphone to chip area usually, these configurations are not suitable for telecommunication and use.In addition, it should be noted, be used for the buffer of hearing aids or amplifier be not configured to provide as use in telecommunication employed muting sensitivity microphone desired high gain level.
The analog input signal that US 6583658-B1 has disclosed first end of self-capacitance formula microphone in a kind of future is transformed into the balancing circuitry structure of symmetrical output signal.First operational amplifier connects into a voltage follower, and its output is as first output signal of symmetrical output signal.Second end of condenser microphone is directly received on the output of second operational amplifier, thereby second output signal of symmetrical output signal is provided.The non-inverting input terminal of second operational amplifier is received on the ground reference, and its inverting terminal is received on the voltage divider that the voltage that is in second and first output signal centre is provided.The symmetry output signal offers the ∑ Δ pattern A/D converter of output bifurcation output signal.
This configuration that is disclosed is being owing to providing the low noise while can handle from the higher voltage level of the ratio of condenser microphone, thereby is convenient.Yet the input impedance of condenser microphone and amplifier is combined and will be formed the filter with the impulse response that can only decay very slowly.Be subjected at microphone the transient state sound of large amplitude or low-frequency degree signal do the time spent will produce the signal component that very slowly changes, input ∑ Δ pattern A/D converter.In ∑ Δ pattern A/D converter, these signal components will produce so-called empty mould sound in the bifurcation output signal.In addition, this configuration is very sensitive to the caused overload of the very uneven signal spectra of distribution that microphone produces.
US 2002/0106091-Al has disclosed a kind of microphone unit that has the internal mode A/D converter.This unit comprises that a sound transducer (condenser microphone that has the electret member) and input are received on the sound transducer and output is connected into the preamplifier of the signal that the input A-D converter is provided.A high pass filter is arranged between preamplifier and A-D converter, be configured to block the DC signal and reduce noise level.In addition, between preamplifier and A-D converter, also disposed a low pass filter, as frequency overlapped-resistable filter.
Though important signal processing aspect has been considered in this configuration, do not solve basic but crucial with in the relevant problem of implementation of performance aspect cost and the noise.This configuration that is disclosed comprises some signal processing levels.Each level all makes noise level increase to some extent.In addition, these grades have taken big chip area, this means that cost is higher.In addition, this configuration is very sensitive to the caused overload of the very uneven signal spectra of distribution that microphone produces.
US 5339285 has disclosed a kind of preamplifier that is used for piezoelectric transducer.This preamplifier is configured to full differential amplifier, and its input is received on the piezoelectric transducer, and its output is for example received on the A-D converter.This preamplifier comprises a common-mode filter feedback configuration, this configuration and the capacitance group of transducer lump together formed one with the integrated high pass filter of preamplifier.This configuration sized is little, has lower noise, and its differential configuration makes that for example silicon base noise (when preamplifier is realized) is rendered as the common-mode signal that can eliminate later on chip.Yet this configuration is not suitable, because Amplifier Gain depends on microphone.In addition, can not make the noise of preamplifier and microphone unit optimization independently.
Summary of the invention
Therefore, an object of the present invention is to provide have as far as possible little input capacitance, alap noise, maximum output amplitude present the preamplifier of as far as possible little chip area simultaneously.
An object of the present invention is to provide a kind of power supply and suppress big and the little preamplifier of distortion.
An object of the present invention is to provide a kind of signal that can handle the slow variation that amplitude is bigger on the input simultaneously can be with the amplifier of the higher low level signal of little distortion amplification frequency.
An object of the present invention is to provide a kind of performance to leakage on the input and the very insensitive amplifier of parasitic couplings.
In addition, also have a purpose to provide the little digital output signal of distortion.
In addition, also have a purpose to provide the preamplifier configuration of the relative microphone circuit independent optimization of a kind of energy.
A kind of integrated circuit that is configured to handle microphone signal is provided, this integrated circuit comprises a preamplifier with an enlarging section and a feedback filter network, the enlarging section has first input end, second input and an output, and the feedback filter network is connected between the output and second input.The first input end of enlarging section has an input impedance, isolate with feedback network basically for input impedance by this input impedance first input end of enlarging section, and preamplifier has the frequency gain transfer function that suppresses low frequency.In addition, it also comprises an A-D converter, connects into reception through the input signal of anti-aliasing filter with digital output signal is provided.
Provide through the input signal of anti-aliasing filter frequency overlapped-resistable filter by the output signal that connects into receiving preamplifier, or because be configured to band pass filter, its high stopband stops the result of anti-aliasing frequency gain transfer function to provide.
Anti-aliasing how realization the no matter, preamplifier is configured to provide the determined frequency gain transfer function that remains unchanged basically, provides the frequency impedance characteristic of the microphone circuit of input signal regardless of being connected to become preamplifier.This is important improvement, because the design and the microphone unit itself of common preamplifier and microphone circuit are contradictory.Particularly because microphone unit is a mechanical component, the difficult control of its electrical property usually, thus microphone unit to have nothing to do with the frequency gain transfer function be favourable.This is applicable to the capacitor type microphone unit that is arranged as the independent chip branch of unit and bearing integrated and the MEMS microphone unit that partly is provided with as the micromachine of MEMS device.Because preamplifier has differential input level (being made up of operational amplifier) usually, therefore can obtain big high impedance.This high input impedance can not be fed filter and destroy, thereby amplifier can not form the load to microphone circuit.
In addition, the intermodulation distortion of the outer low-frequency frequency component introducing of voiced band will be very low.The loop-gain characteristic that feedback configuration provided particularly provides lower distortion.
It should be noted that preamplifier can be presented as single-ended amplifier, be presented as that perhaps differential amplifier or differential differential amplifier or other have the amplifier of several inputs and output.
Yet in a preferred embodiment, preamplifier is configured to differential amplifier.Therefore, advantageously, preamplifier is configured to provide differential output signal by first and second enlarging sections, and preamplifier has a differential mode transfer function that comprises bandpass characteristics.Preamplifier comprises that a foundation is connected to the filter feedback path of inverting terminal separately and the feedback filter network of the filter interconnection vias of setting up the interconnection inverting terminal with the output of each enlarging section.
The differential configuration of preamplifier provides big common-mode rejection ratio and very high input impedance usually.Because the configuration of feedback filter can obtain simply the circuit of frequency gain transfer function to be controlled.Like this, just can there be the big degree of freedom to repair or control transfer function.In addition, differential configuration cooperates permission to use common-mode rejection ratio in the mode relevant with frequency with feedback filter.
Preferably, the low cut-off frequency of the filter of preamplifier realization is arranged to be lower than the low half-power frequency of voiced band.What like this, just can obtain microphone circuit and preamplifier is combined in suitably compromise between the enough short wide and impulse response of voiced band low side die-away time.Impulse response weak point die-away time is favourable, the influence of the low-frequency degree pulse that ping or electrical Interference cause because this has reduced.Otherwise such low-frequency degree pulse can make amplifier and the overload of signal processing circuit subsequently, thereby uncomfortable nonlinear distortion is made us in generation.In an advantageous embodiments, cut-off frequency is arranged on about 10 hertz.
Advantageously, preamplifier has one and comprises that higher cutoff frequency is lower than the differential mode transfer function of 1/2nd bandpass characteristics of the sample frequency of A-D converter.Like this, just can to provide for chip area be that frequency overlapped-resistable filter is realized efficiently to preamplifier.For example, for the sample frequency about 2.4 megahertzes, higher cutoff frequency can be chosen in about the 40-70 kilohertz.In addition, also introduce circuit control to cut-off frequency that can be consistent with the frequency band limits of enlarging section itself.
In one embodiment, preamplifier has a differential mode transfer function that comprises bandpass characteristics, this bandpass characteristics has a nominal passband and a flat gain frequency band, the nominal passband has covered the frequency of voiced band, and the flat gain frequency band has covered the above frequency up to higher cutoff frequency of voiced band.Like this, just can restrain because the noise component(s) that is higher than voiced band that sound/mechanical sources or power supply cause.Therefore, just can protect the preamplifier can be owing to the noise signal of microphone circuit and the gain of resonance peak/amplitude influence is transshipped.Such peak can have for example amplitude about 6dB.
Preamplifier can have a common mode transfer function that comprises low-pass characteristic.Like this, just the common mode DC output level that preamplifier is set at the input of preamplifier can utilized in the common-mode rejection ratio at each frequency place of voiced band.Because the input impedance of preamplifier is very high, therefore can very high ohmage be arranged (for example with one, the 1-20 begohm, the CMOS transistor realization of the reverse mode and range of linearity work a little less than for example being used in) pullup resistor is provided with the DC incoming level, and this can not increase the weight of the load of microphone circuit basically.
In addition, preamplifier can have a common mode transfer function that comprises band resistance characteristic, for low frequency provides smooth gain response.Like this, just can become when low frequency range (being lower than voiced band) and two frequency bands of high frequency (being higher than voiced band) provide common-mode signal to keep DC input setting in preamplifier work.Thereby for resetting, audio sound can reach effective damping to undesirable frequency component.Stopband will comprise voiced band.
In one embodiment, preamplifier has a common mode transfer function and a differential mode transfer function, and preamplifier is arranged such that in its common-mode gain of low frequency preponderates and preponderate in its difference mode gain of voiced band frequency.
In addition, common-mode gain can be preponderated in the frequency of the higher cutoff frequency that is higher than bandpass characteristics.
In an advantageous embodiments, there is a phase shifter to be connected across between the input of the output of first enlarging section and second enlarging section.This is a kind of effective configuration, guarantee hope for example when the difference mode gain of voiced band frequency is preponderated second enlarging section be operated in or near with first enlarging section have 180 the degree phase differences.In addition, phase shifter can be configured to control the DC level of input second enlarging section.This is to realize when phase shifter is included in the input separately of each amplifier and the resistive paths between the output.
Can be that a phase shifter is connected between the input of each enlarging section in addition or also.This configuration also can provide the phase shift of 180 degree, and the DC level of input second enlarging section can randomly be provided on demand.
Preferably, preamplifier comprises the DC biasing circuit that integrates with feedback filter, provides DC skew with the output at preamplifier.This integrated can providing by a voltage divider is received on the AC feedback resistor, voltage divider has the impedance more much lower than AC feedback resistor, for example is about 1/5,1/8 or 1/10 of AC feedback resistor.Perhaps, also can be that the DC skew realizes with the effective current source.
In addition, a DC biasing circuit and feedback filter can be integrated, provide differential mode DC skew with output at preamplifier.Differential mode DC skew is determined by the difference of the direct current biasing that first and second biasing circuits are provided.Like this, just can control the so-called empty mould sound of the A-D converter of ∑ Delta modulator type.The position of empty mould sound and differential mode DC shift into direct ratio (and be by the definite constant of the sampler of ∑ Delta modulator, for sample frequency 1/2nd).
Preferably, A-D converter comprises a ∑ Delta modulator.The noise power spectrum of ∑ Delta modulator (in reality realizes) is distributed in low frequency to be smooth and to be lower Noise Background, but increases in the above noise level of half-power frequency.Because usefulness is heavy over-sampling, so half-power frequency appears at the frequency more much higher than voiced band.Advantageously, modulator provides the serial output signal.
The ∑ Delta modulator can comprise the switching capacity sampler, the differential wave that preamplifier provides is sampled, for the A/D conversion of ∑ Δ provides single-ended input signal, and, make single-ended input signal be superimposed upon on the dc voltage level of being sampled to the dc voltage level sampling.This provides for more or less freely optimization ∑ Delta modulator, because free mould sound control system is arranged in modulator.(and to its control) can be to the signal sampling from preamplifier because sampler, therefore if more complicated slightly just can realize sampling to the DC level.In addition, preamplifier is not born the common mode DC expense that finally will reduce output AC swing.
Preferably, sampler is included as the summing amplifier of an integration section of sampler and ∑ Delta modulator loop.∑ Delta modulator loop is well-known for the personnel that are familiar with this technical field, but for the sake of completeness, it comprises an integration filter that exponent number is given, and being used for provides error signal through integration for the quantizer that semaphore is changed into some discrete levels (for example two, three or four level).
In addition, can provide the integral error feedback signal of ∑ Delta modulator for summing amplifier by first series capacitor, and the dc voltage level be offered summing amplifier by second series capacitor.Like this, empty mould sound just can be with the control recently of the capacitance of first and second series capacitor.The position of empty mould sound is determined by following formula
F
idle＝(V
DC?offsetΣΔ/V
REFΣΔ)＊(C
S1/C
S2)＊1/2?F
s
Wherein, F
IdleBe the position of empty mould sound, C
S1And C
S2Be the capacitance of first and second capacitors, F
sBe sample frequency, V
DC offset Σ ΔBe the dc voltage of being sampled, and V
REF Σ ΔInternal reference for the quantizer in the ∑ Delta modulator.
When A-D converter comprises a ∑ Delta modulator, and when the low-frequency degree pulse that the DC bias voltage level of input ∑ Delta modulator is chosen to make the input preamplifier handle provides the empty mould sound that is higher than voiced band, just can realize reducing significantly nonlinear distortion.The DC bias voltage level is provided by preamplifier, as differential mode DC signal, is perhaps provided by sampler, and is as explained above such.The transient state duration of the impulse response of microphone circuit and this combination of preamplifier is subjected to the restriction of the high pass filter function of preamplifier, and this has further reduced producing the sensitiveness of empty mould sound.
In addition, a kind of microphone is provided, this microphone comprises an integrated circuit as the above proposed and a capacitor microphone unit, and microphone unit is configured to the microphone signal to the response of suffered acoustic pressure is offered the input of microphone preamplifier.Capacitor type microphone unit can be that microphone with electret layer (is the electret capacitor microphone, ECM) or the condenser microphone of DC biasing.
In addition, also provide a kind of microphone, this microphone comprises an integrated circuit as the above proposed and a Micro Electro Mechanical System MEMS microphone unit, will offer microphone preamplifier to the microphone signal of the response of suffered acoustic pressure.
Description of drawings
The present invention will carry out comparatively detailed explanation in conjunction with the preferred embodiments, wherein:
Fig. 1 shows the digital microphone of the preamplifier that comprises microphone unit, has the high pass filter function, frequency overlapped-resistable filter and an A-D converter;
Fig. 2 shows one and comprises microphone unit, has the preamplifier of integrated bandpass filter function and the digital microphone of A-D converter;
Fig. 3 shows one and is included in the microphone that has the differential preamplifier of filter function and phase shifter in first configuration;
Fig. 4 shows one and is included in the microphone that has the differential preamplifier of filter function and phase shifter in second configuration;
Fig. 5 shows first phase shifter;
Fig. 6 shows second phase shifter;
Fig. 7 shows the four port high pass feedback networks that functions of low-pass filter is provided in amplifier;
Fig. 8 shows four a port bands resistance feedback network that bandpass filter function is provided in amplifier;
Fig. 9 illustrates in greater detail a preamplifier with differential mode bandpass filter function and common mode functions of low-pass filter;
Figure 10 shows a preamplifier with differential mode bandpass filter function and common mode functions of low-pass filter, and a differential DC skew wherein is provided;
Figure 11 shows the first frequency gain transfer function of a preamplifier;
Figure 12 shows the second frequency gain transfer function of a preamplifier;
Figure 13 shows the situation that a differential preamplifier back is connected to the switching capacity sampler that integrates with ∑ Δ converter;
Figure 14 shows first configuration of a digital microphone;
Figure 15 shows second configuration of a digital microphone;
Figure 16 shows a single-ended preamplifier and an A-D converter with filter function:
Figure 17 shows a schematic diagram with microphone of integrated circuit and microphone unit;
Figure 18 shows a schematic diagram with microphone of integrated circuit and MEMS microphone unit.
Embodiment
Fig. 1 shows the digital microphone of the preamplifier that comprises microphone unit, has the high pass filter function, frequency overlapped-resistable filter and an A-D converter.Microphone unit C
m105 comprise first member that is rendered as diaphragm or vibrating reed, and the diaphragm response acts on the acoustic pressure motion on it.Relative second component movement of diaphragm, second member are generally so-called backboard or are microphone case simply, but it also is used for keeping dynamic diaphragm.One of them member, normally second member is received on the ground reference, and another member, and diaphragm normally is by receiving DC bias voltage V
MbOn biasing resistor R
Mb104 are setovered.Like this, electric charge just is provided to microphone unit 105C
mDiaphragm or movable link on.Because the quantity of electric charge keeps constant (for very low frequency and the frequency more than the very low frequency), diaphragm just provides electric microphone signal when moving in the suffered acoustic pressure effect of response.The microphone signal that causes owing to motion of membrane is superimposed upon on the caused DC signal of biasing.The circuit that comprises microphone unit 105, biasing resistor 104 and blocking capacitor has been formed microphone circuit 107.
Microphone signal offers the input φ of preamplifier 101 by blocking capacitor 106, and blocking capacitor 106 prevents that the DC offset signal from arriving on the input of this preamplifier.
The feature of preamplifier 101 is to have the high pass gain characteristic, and is smaller and bigger for the frequency gain in the voiced band for the frequency gain that is lower than voiced band.Preferably, gain characteristic below voiced band with single order, second order, three rank, quadravalence or more high-order descend.Preferably, the cut-off frequency of low pass gain characteristic is approximately 10 hertz.In addition, the feature of this amplifier is that the low frequency microphone signal is treated to common-mode signal (common-mode signal) and the high frequency microphone signal is treated to difference mode signal (differential mode signal).Therefore, suppressed low frequency component effectively.For low half-power frequency is 20 hertz voiced band, low frequency be 5-20 conspicuous about following frequency, and the high frequency conspicuous above frequency that is 10-30.
The output of preamplifier 101 is as output
With
On differential wave, offer ∑ Δ A/D converter 103 by frequency overlapped-resistable filter AAF 102.∑ Δ converter provides the over-sampling that is designated as Do 1 bit output signal.∑ Δ converter with 2.4 megahertzes about or higher sample frequency carry out work.
The digital microphone of Fig. 1 can be subjected to occurring in its environment has bigger amplitude and has the effect of sound of the amplitude slope of steeper in time domain.This sound can because close car door with strength, remote communicating device falls to wait on the table and causes, generation is comprised the input signal of the low-frequency degree signal of some large amplitudes.When microphone is received on its power supply, the circuit of microphone will be subjected to the effect of the power pulse of step-like.This also is expressed as one and starts or add electric pulse, and it will produce a signal that comprises low-frequency degree (input) signal of large amplitude equally.
At analog domain, the electric capacity of biasing resistor Rmb and microphone unit forms a high pass filter, and its impulse response has the relatively shorter rise time but long fall time.As a result, just having the low-down pulse of frequency (can think it almost is direct current) rests on the input of preamplifier.Unless revise this impulse response, the output signal of microphone is in seriously distortion of numeric field.
At analog domain, wish biasing resistor Rmb is designed to have big ohmic value usually with regard to considering noise, for example for the hundreds of megaohm to gigabit or teroihm magnitude.The typical capacitance value of microphone is combined to produce with big biasing resistor and is approximately 0.01 hertz low cut-off frequency.Be approximately a few minutes this fall time that is equivalent to impulse response.Therefore, big ping the input of preamplifier produce a decay but want the DC current potential that a few minutes just attenuate.In addition, because preamplifier provides 0dB the gain of above (for example being 6dB), if therefore there is not the high pass filter function of preamplifier, this gain meeting is set up even higher DC level at the output of amplifier.
The high pass filter function of preamplifier has been introduced and has been approximately 10 hertz low cut-off frequency.The impulse response that this filter of preamplifier makes microphone unit and preamplifier combine decays sooner, and is faster than 0.5 second usually.Therefore, the input of ∑ Δ converter can not be subjected to the effect of slow DC level of decaying and only can be subjected to the effect of the pulse of decay fast.
∑ Δ converter is provided at the output signal Do in the numeric field.This output signal has the power spectrum that comprises smooth Noise Background.Be higher than the noise half-power frequency, noise level increases gradually with frequency.The characteristic of ∑ Δ converter makes the DC level-sensitive of converter to above-described low-frequency degree signal, because main sound occurs in the power spectrum of digital output signal.These sounds make the serious distortion of playback of the voice signal in the digital output signal.These sky mould sounds must be controlled, so that the good sound reproduction in numeric field to be provided.
Fig. 2 shows one and comprises microphone unit, has the preamplifier of integrated bandpass filter function and the digital microphone of A-D converter.Microphone unit 105 is included in the microphone circuit 107, as explained abovely carries out work like that.
Therefore, the feature of this preamplifier be have smaller for the frequency gain below the voiced band, bigger and for the smaller frequency gaining characteristic of the frequency gain more than voiced band for the frequency gain in the voiced band.Preferably, frequency gaining characteristic is being lower than and is being higher than the range of audibility by single order, second order, three rank, quadravalence or more high-order decline.In addition, the feature of amplifier is that the low frequency microphone signal is treated to common-mode signal and the high frequency microphone signal is treated to difference mode signal.So just suppressed low frequency component effectively.Therefore, this preamplifier has been realized a band pass filter.Below, also this preamplifier is called differential preamplifier.
The function of band pass filter amplifier be blanketing frequency the signal below the passband (being voiced band) with the input stage overload of avoiding differential amplifier and the frequency 1/2nd or more that is suppressed at about Nyquest frequency with avoid signal subsequently to the output of band pass filter amplifier sample with digitlization in the aliasing problem that occurs.So just do not need an independent frequency overlapped-resistable filter.
Fig. 3 shows one and is included in the microphone that has the differential preamplifier of filter function and phase shifter in first configuration.Differential preamplifier 306 is shown has input φ and output
With
Preamplifier is connected with microphone circuit 107, and its input φ receives microphone signal from microphone circuit 107.
Preamplifier is configured to the amplifier of an instrumented, has one by the impedance Z 1, Z2 and the Z2 that are designated as 305,303 and 304
*The filter feedback network of forming and have a phase shifter network 307.Impedance Z 2 303 is connected on output
And between the inverting terminal of operational amplifier 301.Impedance Z 2
*304 are connected into the similar feedback of operational amplifier 302.Impedance Z 1 is connected between the non-inverting input terminal of the inverting terminal of amplifier 301 and amplifier 302.The filter feedback network has been set up the high pass filter function or the bandpass filter function in its differential mode of differential preamplifier.Impedance Z 1, Z2 and Z2
*With can be used for the element realization that chip is realized, provide capacitive character or resistive effect or their combination effect.
Phase shifter network PD (f) 307 has the input port that is designated as (a) and is designated as the output port of (b).Input port (a) is received on the inverting terminal of first operational amplifier 301, and output port (b) is received on the inverting terminal of second operational amplifier 302.The phase shifter network is realized the phase shift relevant with frequency, about high frequency phase shift ± 180 degree, and about low frequency phase shift 0 degree.Like this, just guaranteed that the differential mode output signal shows as common-mode signal and shows as real difference mode signal at high frequency region at low frequency range.Phase shift provides effective high-pass filtering like this, because force output signal at low frequency range and be common-mode signal at low frequency range only.
This configuration of preamplifier is easily, because the input of phase shifter is received on the input of preamplifier by the inverting terminal of operational amplifier 301.
Yet in the another kind configuration, the input of phase shifter is received on the circuit node of setting up between the input of microphone unit 107 and preamplifier (the non-inverting input terminal place of operational amplifier 301).
Should be pointed out that feedback filter can realize with active filter and/or active DC server.
Fig. 4 shows one and is included in the microphone that has the differential preamplifier of filter function and phase shifter in second configuration.This configuration is quite near the configuration shown in Fig. 3, and just phase shifter 307 is connected between the non-inverting input terminal of the output of first operational amplifier 301 and second operational amplifier.
Therefore, the phase shifter as described above 307 shown in Fig. 3 and 4 is connected between two common mode amplifiers of differential preamplifier across.
Fig. 5 shows first phase shifter.Phase shifter 307 and an operational amplifier are combined realization, form a low-pass first order filter, low frequency range provide 0 the degree about phase shift and high frequency region provide 180 the degree about phase shift.
Fig. 6 shows second phase shifter.In this embodiment, phase shifter 401 and an operational amplifier are combined realization, form a band pass filter (BPF), the phase shift about low frequency provides 0 to spend, phase shift about intermediate frequency provides 180 to spend, and the phase shift about high frequency provides 0 to spend.Intermediate frequency is defined as and comprises voiced band and the high frequency that arrives the higher cutoff frequency of band pass filter.Higher cutoff frequency is usually designed to and is near the limit that operational amplifier introduces.The above frequency of higher cutoff frequency is called high frequency.
Phase shifter 401 forces the output of preamplifier
With
Show as at low frequency range with at high frequency region and to be in common mode.At intermediate frequency zone, phase shifter permission preamplifier shows as and is in differential mode.Like this, the preamplifier with phase shifter network provides effectively the differential mode to low frequency and high frequency to suppress.Therefore, also provide an effective frequency overlapped-resistable filter.
Phase shifter comprises capacitor 603 and the resistor 601 that is connected in parallel, and forms a signal path between input port (a) and output port (b).Series capacitors 602 and resistor 604 provide a signal path between output port (b) and ground.
No matter phase shifter PD (f) makes single order, second order or the phase shifter of high-order more, all can guarantee at low frequency and high frequency but very not little in the difference mode gain of intermediate frequency.Phase shifter provides so very little gain by introduce at least one zero point and limit that is in the frequency that is higher than voiced band that is in 0 hertz (DC) in the transfer function of preamplifier filter.
Fig. 7 shows the four port high pass feedback networks that functions of low-pass filter is provided in amplifier.This feedback network comprises port (a) and (b), (c) and (d).From (b) to (a) and the feedback path from (d) to (c) are respectively by capacitor C2 701 and C2
*704 set up.
Set up being connected in series of a capacitor and resistor by C1 703 and R1 702 at port (a) and (c).This is connected in series and connects the input of enlarging section 301 and 302.
Fig. 8 shows four a port bands resistance feedback network that bandpass filter function is provided in amplifier.This feedback network comprises port (a) and (b), (c) and (d).From (b) to (a) and the feedback path from (d) to (c) are set up by the capacitor 802 that is connected in parallel, resistor 801 and the capacitor 805 that is connected in parallel, resistor 806 respectively.
Capacitor C1 804 and resistor R 1 803 be connected in series in port (a) and (c) between.This is connected in series and connects the input of enlarging section 301 and 302.
Yet, it should be noted, other feedback filter configurations also can be provided, include source filter and/or higher order filter.
Fig. 9 illustrates in greater detail a preamplifier with differential mode bandpass filter function and common mode functions of low-pass filter.Preamplifier 901 in configuration as shown in Figure 4, comprise with the corresponding AC feedback network shown in Fig. 8 and with the corresponding phase shifter network shown in Fig. 5.Feedback network and phase shifter have been set up differential mode high pass filter function.The DC feedback network that integrates therewith provides the common mode functions of low-pass filter, and it provides definite common-mode gain for DC and low frequency.This preamplifier is arranged such that in the impedance of DC (low frequency) DC feedback network preponderates, and preponderates in the impedance of high-frequency AC feedback network.Like this, provide the DC level of differential wave just can when realizing desirable AC filter function, control with very limited circuit.
Benchmark dc voltage level Vb is added to the input of preamplifier, and preamplifier determines that with its common mode DC gain foundation provides definite DC level of differential wave.
The input φ of preamplifier 901 receives on the microphone circuit 107, and in check dc voltage level is added on this input by resistor R b 902 by the voltage source (not shown).This dc voltage level is according to the common mode DC gain setting of desirable common mode DC output level and preamplifier.It should be noted for this reason, give the power supply of microphone normally single-ended, promptly at nominal supply voltage level V
DdTo between the ground reference level.For the symmetry constraint to the AC output voltage swing is provided at differential mode, common mode DC output level should be near 1/2nd of nominal supply voltage.So just can reach maximum differential mode AC voltage swing.To this respect is ben, because this restriction is restrictive in order to obtain the big AC tool that gains.In addition, owing to the increase of the noise in the digital microphone signal along with pregain reduces, therefore big pregain (and big AC voltage swing space) is preferred.It should be noted that bigger AC signal swing can improve signal to noise ratio, because the noise of being introduced by ∑ Δ converter for different amplitudes is constant.
Because the input stage of preamplifier will be saturated in the time spent of doing of the input DC level that is subjected to comparing big with supply voltage usually, therefore export the DC level and must use DC pregain to obtain greater than 0dB.
For example, if the nominal supply voltage level is 1.5 volts, common mode DC output level should be approximately 1.5 volts 1/2nd, promptly 0.75 volt.For 1.5 volts supply voltages and the differential typical input stage to type of PMOS, input should be able to be handled the input dc voltage level up to approximate 0.4 volt.In order to set the DC level of output, the DC gain should be at least about twice.0.75 the DC output level of volt and the DC of twice gain require DC reference voltage V b to equal 0.375 volt, and be littler than 0.4 volt.
This preamplifier is made by two operational amplifiers 903 and 904 differential preamplifiers of forming.
The DC gain of differential preamplifier is realized by the other DC feedback network of these two operational amplifiers.The DC feedback network detects separately output signal with voltage divider.Voltage divider is realized for operational amplifier 903 usefulness resistors 906 and 907 and is realized for operational amplifier 904 usefulness resistors 909 and 908.
The AC feedback network is configured to as shown in Figure 8.Yet because it and DC network integration are together, so the resistive feedback path of AC network comprises resistor 910,906 and the resistor 909,913 that is respectively applied for amplifier 903 and 904. Capacitor 905 and 914 and the resistive feedback path be connected in parallel.Capacitor 911 and resistor 912 are connected in series between the inverting terminal of amplifier 903 and 904.
Phase shifter configuration becomes as shown in Figure 5.Yet, since desirable be with it with the DC network integration together, so its its input of circuit nodes reception from setting up by voltage divider 906 and 907.
At DC, the impedance of DC feedback network is preponderated.Therefore, from the DC isoboles, the voltage that is provided by voltage divider 906,907 is actual identical with the voltage of the inverting terminal that feeds back to amplifier 903.As a result, the DC of amplifier 903 gain is determined by voltage divider.The DC gain of twice for example realizes with two 100 kilo-ohms resistor.Equally, the DC of amplifier 904 gain is determined by resistor 909 and 908.This DC gain is chosen to the gain coupling with amplifier 903.
In addition, provide the identical output voltage of level with amplifier 903 in order to force amplifier 904, the resistor 912 of phase shifter is received on the circuit node of being set up by voltage divider 906,907.Like this, the output level that the output level of amplifier 904 will follow-up amplifier 903.
As another embodiment, can in the input stage of amplifier 903, for example introduce DC biasing or DC bias voltage by the differential source voltage level (thereby also just being offset grid and drain voltage) in the skew input stage to the PMOS device.This embodiment can based on top illustrated similar DC and AC feedback network.In this case, Vb ground connection is so that set the DC bias level.It should be noted that the combination of these two kinds of configurations also is feasible.
At AC, the impedance of AC feedback network is preponderated.Therefore, from the AC isoboles, feedback filter and phase shifter are as carrying out work in conjunction with Fig. 4,5 and 8 illustrated.Yet, recall, comprise that the phase shifter network configuration of resistor 512 and capacitor 513 becomes to provide to move gradually the phase place of the signal of input phase shifter.This has guaranteed that preamplifier provides common mode output signal at the low frequency that comprises DC, and is comprising that voiced band and the high frequency that is higher than the frequency of voiced band provide difference mode signal.
Realize by capacitor 916 and resistor 915 in operational amplifier 903 other sides of forming of differential amplifier and the phase shift between the operational amplifier 904 other opposite sides of forming.Therefore, just can obtain such phase shift with a phase shifter.It should be noted that resistor 915 is connected with capacitor 916 and set up a limit (F
P2) and one zero point (F
Z1), as described below.
Figure 10 shows a preamplifier with differential mode bandpass filter function and common mode functions of low-pass filter, and differential DC skew wherein is provided.In the configuration of the preamplifier illustrated in conjunction with Fig. 9, common mode DC output by the input of preamplifier or operational amplifier 903 and 904 or the dc voltage benchmark that provides of one of them input stage provide.Combination therewith, common mode DC output is determined by the common mode DC gain of dc voltage benchmark and preamplifier.
Yet two the effective current sources 1001 of preamplifier 1001 usefulness and 1002 shown in Figure 10 provide common mode DC skew.In addition, differential mode DC is offset the difference between currents of being drawn by two current sources provides.Because ∑ Δ converter connects into the differential wave that detection is provided by preamplifier 1001, therefore empty mould sound can be by the differential mode DC skew control that provides in preamplifier.
When the DC skew was provided by effective current source 1001,1002, no matter it is differential mode or common mode DC was offset or the two, and input should (be V by input is set to reference level by resistor 902 ground connection for example
b=0 volt; Yet V for reality realizes
bShould be at least about 100 millivolts).Yet, also can apply another DC benchmark and cooperate with the effective current source.
For example, if supply voltage V
DdBe single-ended 1.5 volts and benchmark V
bBeing set to 0 volt, can be 1/2 V by drawing via resistor 906 that the DC electric current that forms 0.75 volt dc voltage at its two ends obtains just
Dd=0.75 volt common mode dc voltage.For example, resistor 906 has 100 kilo-ohms resistance, and 7.5 microamperes electric current will be at output (output
) this desirable dc voltage is provided.
In addition, if wish to set up 15 millivolts differential mode DC skew about optimizing empty mould sound, and the resistance of resistor 909 is substantially equal to the resistance of its antithesis resistor 906, and 7.35 microamperes electric current will be at the output (output of amplifier 904
) on provide one to be 0.735 volt dc voltage.So just set up 15 millivolts differential mode DC output, as desired.
From AC, phase shifter PD (f) constitutes with resistor 1003 and capacitor 1004 as shown in Figure 5, embeds preamplifier, and what illustrate as among Fig. 3 is such.Therefore, resistor 1003 is received on the non-inverting input terminal of the inverting terminal of operational amplifier 903 and operational amplifier 904.Capacitor 1004 is connected between the non-inverting input terminal and ground reference of amplifier 904.
Thereby preamplifier connects at AC and forces the low frequency output signal to be rendered as common-mode signal and when high frequency forces output signal to be rendered as difference mode signal, the differential mode DC level that is provided for making the common mode DC level of output AC voltage swing maximum and is used to control empty mould sound.
In another embodiment, differential mode DC skew can be connected on output with one
And the voltage divider between the ground is realized.The circuit node that this voltage divider is connect at resistor 1003 (rather than resistor 1003 is received on the inverting terminal of amplifier 903) provides an output voltage through dividing potential drop.
Figure 11 shows the first frequency gain transfer function of preamplifier.Show as for preamplifier and to be in common mode (A
CM=curve 1) and differential mode (A
DM=curve 2) situation shows the correspondent frequency gain.The straight line that response is shown on logarithm frequency axis and log gain axle is approximate.
Resistors in series C1 702,804 in the feedback network has introduced limit-zero point to (F
P2, F
Z2).Set up from F being arranged on usually about the 50-60 kilohertz this limit-zero point
Z2To the F that is in about 500 kilo hertzs
P3The gain steady section, introduce at least one limit at 500 kilo hertzs of left and right sides amplifiers itself, thereby introduced a negative slope.
Voiced band is with hanging down half-power frequency F
ALWith high half-power frequency F
AUIllustrate.
Figure 12 shows the second frequency gain transfer function of preamplifier.Equally, show as for preamplifier and be in common mode (A
CM=curve 1) and differential mode (A
DM=curve 2) situation shows the correspondent frequency gain.
Figure 13 shows the situation that the differential preamplifier back is connected to the switching capacity sampler that integrates with ∑ Δ converter.Differential preamplifier 201 receives microphone signal on its input φ, the output of antithesis is provided
With
The signal that preamplifier provides by these two outputs differential sampling of switching capacity detector that integrates with ∑ Δ converter 103.The switching capacity detector configurations is other at operational amplifier 1301.Differential sampling realizes by be connected on two input series capacitor 1305 and feedback condensers 1304 between the circuit arrangement by switch S 1-S4.
Switch S 1-S4 is controlled to the closed or disconnection according to the mode shown in Figure 13 lower right corner, and promptly switch S 1 is consistent with S3 moves, and moves but relative S1 and S3 phase deviation 180 degree and switch S 2 is consistent with S4.Switch S 1-S4 is with for example sample frequency control of ∑ Δ converter of clock frequency.The sampling of the switching capacity of differential wave is to be familiar with here not elaborating known to the personnel of this technical field, but illustration the interconnection situation of differential preamplifier and ∑ Δ converter.
It should be noted that amplifier 1301 connects into the summing amplifier of realizing ∑ Δ feedback control loop by capacitor 1303.The personnel that are familiar with this technical field know what how the ∑ Delta modulator normally disposed.The professional and technical personnel knows that summing amplifier compares input signal with the feedback signal that obtains from the quantizer that digital output signal Do is provided.The output of summing amplifier is received on the integrator (no matter it is several rank), and integrator offers quantizer with its output signal.Feedback signal offers summing amplifier 1301 by capacitor 1303.
Except switching capacity sampling, also realized a kind of execution mode of DC skew to differential wave.The execution mode of this DC skew can replace providing differential DC skew in preamplifier, be configured to the empty mould sound of ∑ Δ converter is controlled.
The DC skew can be embodied as single-ended DC skew in this level of digital microphone.It is 1306 pairs of dc voltage benchmark of the series capacitor V that alternately receives on dc voltage benchmark and the ground reference by using
DC offset Σ Δ Sampling realizes.Capacitor 1306 usefulness switch S 5 alternately are connected with S6.The switching mode of switch S 5 and S6 is controlled by the logical network on the output of receiving the quantizer in the ∑ Δ converter.
In this illustration, frequency overlapped-resistable filter is to realize by the higher cutoff frequency that the band pass filter of preamplifier is realized.Needed is the spectrum component of eliminating the sample frequency that is higher than converter.
Therefore, can the integral error feedback signal of ∑ Delta modulator be provided and provide the dc voltage level for summing amplifier for summing amplifier by first series capacitor by second series capacitor.Like this, empty mould sound just can be with the control recently of the capacitance of first and second series capacitor.The position of empty mould sound is determined by following formula:
F
idle＝(V
DC?offset?ΣΔ/V
REF?ΣΔ)＊(C
1306/C
1304)＊1/2?F
S
Wherein, F
IdleBe the position of empty mould sound, C
1306And C
1304Be the capacitance of first and second capacitors, F
SBe sample frequency, V
DC offset Σ ΔBe the dc voltage of being sampled, and V
REF Σ ΔInternal reference for the quantizer in the ∑ Delta modulator.
When A-D converter comprises a ∑ Delta modulator, and hank the low-frequency degree pulse that makes the input preamplifier handle when the empty mould sound that is higher than voiced band is provided in the DC bias voltage level of input ∑ Delta modulator, just can reduce the nonlinear distortion in the digital microphone significantly.The DC bias voltage level is provided by preamplifier, as differential mode DC signal, is perhaps provided by sampler, and is as explained above such.The duration of the impulse response of the combination of microphone circuit and preamplifier is limited by the high pass filter function of preamplifier, and this has further reduced producing the sensitiveness of empty mould sound.
Figure 14 shows first configuration of digital microphone.Realize that for condenser microphone digital microphone is encapsulated in the box 1401 that is packaged with the integrated circuit that is rendered as chip 1402.Chip 1402 comprises respectively terminal Tc1, Tc2, Tc3, the Tc4 that is connected with supply voltage with microphone unit 1408, bias voltage, ground reference current potential.Terminal Tc6 provides the digital microphone output signal Do from the A/D converter.Clock signal offers the A/D converter by terminal Tc5.Can provide for the supply voltage of amplifier 1405 and A/D converter by terminal Tc6, terminal Tc4 can save in this case.
Realize that for the condenser microphone box microphone unit 1408 is condenser microphones, it needs a DC bias generator suitable electric charge is provided on the member in the microphone component.This DC bias voltage provides by resistor 1403.Blocking capacitor 1404 stops the DC bias level to be added to the input stage of preamplifier 905.In another embodiment, microphone unit 1408 is electret capcitor microphone ECM.Thereby microphone unit 1408 is directly received the input and the bias resistor of preamplifier 1405, does not need blocking capacitor.
Realize that for Micro Electro Mechanical System MEMS digital microphone is made a MEMS device, it comprises a microcircuit part and a micromachine part, realizes microphone unit 1408.From circuit, microphone unit has changed the position of circuit and blocking capacitor.Microcircuit part or chip unit depend on the circumstances, and comprise a preamplifier 1405 and the A/D converter 1407 with bandpass filter function.
Figure 15 shows second configuration of digital microphone.It should be noted that below explanation is applicable to the realization with the digital microphone of chip and condenser microphone.Yet according in conjunction with the explanation that Figure 14 did, the personnel that are familiar with this technical field can finish MEMS and realize.
Booster converter voltage pump UPC 1004 in other words can be rendered as so-called Dickson converter form.Voltage pump is by oscillator operation, and oscillator is preferably voltage pump provides the square wave oscillator signal.Can be with other signals with low harmonic components, for example sinusoidal wave or through the square wave of filtering, obtain lower noise.In another embodiment, oscillator is embedded on the chip 1502.
As shown in the figure, the same oscillator/clock signal that provides by terminal Tc4 is provided for booster converter and ∑ Δ converter.It should be noted, this Signal Separation can be obtained different vibration/clock signal frequencies, offer UPC and ∑ Δ converter.
Figure 16 shows single-ended preamplifier and A-D converter.In this embodiment, microphone circuit 107 offers single-ended preamplifier 1602 with signal.The output of preamplifier 1602 offers the A-D converter 103 of ∑ Delta modulator type.
The frequency gaining characteristic of feedback filter 1603 has low-pass characteristic, thereby realization has the high pass filter characteristic of the preamplifier of feedback filter.Preferably, the passband of feedback filter (low frequency) provides quite smooth gain response to DC.For upper frequency, more than its gain transition band, provide flat response to high frequency.This is illustrated by feedback filter.
Yet it is consistent that the frequency gain transfer function can be configured to after having done necessary change the transfer function with differential amplifier.
Figure 17 shows a schematic diagram with microphone of integrated circuit and microphone unit.Microphone is shown the pick-up head with microphone component, comprises microphone diaphragm and integrated circuit.
Figure 18 shows a schematic diagram with microphone of integrated circuit and MEMS microphone unit.Microphone 1902 comprises and is integrated in the first suprabasil MEMS microphone component 1903 and is integrated in the second suprabasil preamplifier circuit 1901.Preamplifier circuit comprises one of above different embodiment that disclose, and comprises that promptly one has the preamplifier of feedback circuit and for example voltage pump and/or feedback circuit, and wherein preamplifier is a differential amplifier or single-ended amplifier.
It should be noted that MEMS microphone component 1903 and microphone preamplifier 1901 can be integrated at same the semiconductor-based end.
Usually it should be noted that preamplifier can be made single-ended amplifier, differential amplifier or other amplifier types such as differential differential amplifier.Have in use under the situation of preamplifier of several input and output, the difference of a plurality of feedback filter paths realizes realizing desirable frequency transfer function.
Condenser microphone comprises very light diaphragm and is added with the backboard of polarizing voltage.Thereby provide the electric charge of constant (with respect to relevant frequency).Operation principle is that the sound wave that is applied on the diaphragm changes the electric capacity between diaphragm and the backboard thereupon.Thereby this induces AC voltage on backboard.
Electret capcitor microphone ECM works in a similar fashion, just has a permanent charge voltage that injects electret, is used to provide polarizing voltage.This can realize that prevailing is when diaphragm is electret in three kinds of modes, and a side is metallized in this case.This is called film or diaphragm-type.Electret can not be manufactured best diaphragm, higher if desired performance, and diaphragm other materials manufacturing, and electret is added on the backboard.This back type that is called.Comparatively recently, modification is so-called just preceding type.At this moment, electret is added in the inboard of microphone protecgulum, and metallized diaphragm is received the input of preamplifier.
Voiced band may be prescribed as any frequency band in the voiced band of typical definition.Typical definition can be 20 hertz to 20 kilo hertzs.The exemplary low cut-off frequency of voiced band can be 20 hertz, 50 hertz, 80 hertz, 100 hertz, 150 hertz, 200 hertz, 250 hertz.The exemplary high half-power frequency of voiced band can be 3 kilo hertzs, 5 kilo hertzs, 8 kilo hertzs, 10 kilo hertzs, 18 kilo hertzs, 20 kilo hertzs.The so-called quite smooth variation that is meant gain response greatly about+/-1dB ,+/-3dB ,+/-4dB ,+/-6dB in.Yet available other changing values define so-called " quite smooth ".
More than disclosed different preamplifier configurations.These configurations comprise different I/O end configurations, for example two-terminal configuration.Yet, it should be noted, can be for providing three, four or more a plurality of terminal with signal I/O microphone and preamplifier.It should be noted especially, can provide independent terminal for supply voltage (at the first end place) and preamplifier output (at the second end place).Under the situation of differential preamplifier output, except a terminal that is used for power supply, can also provide two terminals that are used for output signal.Can provide an independent terminal for ground reference.This ground reference normally but is always shared by power supply and output signal.
Claims (20)
1. integrated circuit that is configured to handle microphone signal, described integrated circuit comprises:
Have the preamplifier (306) of enlarging section (301) and feedback filter network, enlarging section (301) have differential input terminal and the output that comprises the first input end (+) and second input (-)
The feedback filter network is connected on output
And between second input (-); Wherein the first input end (+) of enlarging section (301) is received the input that is used to receive microphone signal (φ) of preamplifier, wherein preamplifier has the frequency gain transfer function that suppresses the low frequency in the stopband with respect to the upper frequency in the passband, and wherein preamplifier (306) is configured to provide differential output signal of common mode and the interior differential output signal of differential mode of passband in the stopband; And
A-D converter connects into from preamplifier and receives as through the differential output signal of the signal of anti-aliasing filter with digital output signal is provided.
2. integrated circuit according to claim 1, wherein,
Described preamplifier (306) is configured to provide differential output signal by first and second enlarging sections (301,302)
Described preamplifier (306) has the bandpass characteristics of comprising (A
DM) the differential mode transfer function, and
Described preamplifier (306) comprises feedback filter network (303,304,305), and this network is set up the filter feedback path (a-b that the output of enlarging section (301,302) is connected to inverting terminal separately; And set up filter interconnection vias (a-c) c-d), with described inverting terminal interconnection.
3. integrated circuit according to claim 1 and 2, the low cut-off frequency (F of the filter that wherein said preamplifier (306) is realized
P1) be arranged to be lower than the low half-power frequency of voiced band.
4. integrated circuit according to claim 1 and 2, wherein said preamplifier (306) has the higher cutoff frequency of comprising (F
P3F
P2) be arranged to be lower than the sample frequency (F of A-D converter
S) the differential mode transfer function (A of 1/2nd bandpass characteristics
DM).
5. integrated circuit according to claim 1 and 2, wherein said preamplifier (306) have the differential mode transfer function (A that comprises following bandpass characteristics
DM), this bandpass characteristics has a nominal passband (F
P1-F
P2) and a gain steady section frequency band (F
Z2-F
P3), wherein the nominal passband cover the voiced band frequency and the steady section frequency band that gains to cover voiced band above up to higher cutoff frequency (F
P3) frequency.
6. integrated circuit according to claim 1 and 2, wherein said preamplifier (306) have the common mode transfer function (A that comprises low-pass characteristic
CM).
7. integrated circuit according to claim 1 and 2, wherein said preamplifier has the stopband characteristic of comprising (F
Z1 '-; F
Z1 '-F
Z2 ') common mode transfer function (A
CM), be low frequency (DC-F
P1 ') a smooth gain response is provided.
8. integrated circuit according to claim 1 and 2, wherein said preamplifier have common mode transfer function (A
CM) and differential mode transfer function (A
DM), these transfer functions are configured at low frequency (DC-F
P1 ') its common-mode gain (A
CM) preponderate and at voiced band frequency (F
AL-F
AU) its difference mode gain (A
DM) preponderate.
9. integrated circuit according to claim 8, wherein said common-mode gain (A
CM) also be higher than the higher cutoff frequency (F of bandpass characteristics
P2, F
P3) frequency preponderate.
10. integrated circuit according to claim 2 wherein has a phase shifter (307) to be connected across between the input of the output of first enlarging section (301) and second enlarging section (302).
11. integrated circuit according to claim 2 wherein has a phase shifter (307) to be connected between the input separately (-) of each enlarging section (301,302).
12. integrated circuit according to claim 1 and 2, wherein said preamplifier comprise one and feedback filter (Z1; Z1, Z1
*, the DC biasing circuit (907,908 that Z2) integrates; 1001,1002), be used for providing DC skew at the output of preamplifier.
13. integrated circuit according to claim 1 and 2, described integrated circuit also comprise a DC biasing circuit (907,908 that integrates with feedback filter; 1001,1002), be used for providing differential mode DC skew at the output of preamplifier.
14. integrated circuit according to claim 1 and 2, wherein said A-D converter comprise a ∑ △ modulator (103).
15. integrated circuit according to claim 14, wherein said ∑ △ modulator (1302) comprises a switching capacity sampler (1307), the differential wave that it is provided preamplifier (201)
Sampling thinks that ∑ △ A/D conversion provides single-ended input signal, and to dc voltage level (V
Ref Σ Δ) sampling, make this single-ended input signal be superimposed upon on the dc voltage level of being sampled.
16。Integrated circuit according to claim 15, wherein said sampler comprise that one is the summing amplifier (1301) of an integration section of sampler (1307) and ∑ △ modulator loops.
17. integrated circuit according to claim 16, wherein said summing amplifier (1301) is provided with the integral error feedback signal that ∑ △ modulator provides by first series capacitor (1303), and described dc voltage level offers summing amplifier (1301) by second series capacitor (1306).
18. integrated circuit according to claim 1 and 2, wherein said A-D converter comprises a ∑ △ modulator, and the DC bias voltage level of input ∑ △ modulator is selected such that the low-frequency degree pulse that inputs to preamplifier (201) processing provides the empty mould sound that is higher than voiced band.
19. microphone (108; 202), described microphone comprises that capacitor type microphone unit (105) is configured in response to its suffered acoustic pressure microphone signal be offered the input (φ) of microphone preamplifier (201) according to described integrated circuit of above arbitrary claim and capacitor type microphone unit (105).
20. a microphone, described microphone comprise that according to described integrated circuit of above arbitrary claim and MEMS microphone unit, the MEMS microphone unit offers microphone preamplifier in response to its suffered acoustic pressure with microphone signal.
Applications Claiming Priority (3)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US54230504P | 2004-02-09 | 2004-02-09 | |
| US60/542,305 | 2004-02-09 | ||
| DKPA200401531 | 2004-10-06 |
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|---|---|
| CN1938941A CN1938941A (en) | 2007-03-28 |
| CN100521518C true CN100521518C (en) | 2009-07-29 |
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| CNB2005800043951A Expired - Fee Related CN100521518C (en) | 2004-02-09 | 2005-02-09 | Digital microphone |
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|---|---|---|---|---|
| CN102026062B (en) * | 2010-07-30 | 2014-06-25 | 炬力集成电路设计有限公司 | Integrated circuit, method and chip for microphone signal preamplification as well as electronic equipment |
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| CN109862497A (en) * | 2017-11-30 | 2019-06-07 | 北京七九七华音电子有限责任公司 | A kind of microphone |
| CN108134582B (en) * | 2018-01-25 | 2022-02-18 | 郑州云海信息技术有限公司 | Analog front-end circuit |
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| CN109858191B (en) * | 2019-03-13 | 2023-09-26 | 江西理工大学 | Generalized chaotic synchronization system construction and circuit design method |
| CN110277967A (en) * | 2019-06-28 | 2019-09-24 | 瓴盛科技有限公司 | A kind of integrated circuit and the mobile terminal including the integrated circuit |
| CN110750057A (en) * | 2019-12-26 | 2020-02-04 | 江西飞尚科技有限公司 | Single-power-supply synchronous data acquisition device and acquisition method thereof |
| CN112274174A (en) * | 2020-10-25 | 2021-01-29 | 贵州大学 | Intelligent electronic auscultation control system, method, storage medium and electronic stethoscope |
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| CN1938941A (en) | 2007-03-28 |
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