CN110190816B - Self-feedback low-noise amplifier applied to biopotential treatment - Google Patents
Self-feedback low-noise amplifier applied to biopotential treatment Download PDFInfo
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- CN110190816B CN110190816B CN201910309710.5A CN201910309710A CN110190816B CN 110190816 B CN110190816 B CN 110190816B CN 201910309710 A CN201910309710 A CN 201910309710A CN 110190816 B CN110190816 B CN 110190816B
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- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03F—AMPLIFIERS
- H03F1/00—Details of amplifiers with only discharge tubes, only semiconductor devices or only unspecified devices as amplifying elements
- H03F1/02—Modifications of amplifiers to raise the efficiency, e.g. gliding Class A stages, use of an auxiliary oscillation
- H03F1/0205—Modifications of amplifiers to raise the efficiency, e.g. gliding Class A stages, use of an auxiliary oscillation in transistor amplifiers
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- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03F—AMPLIFIERS
- H03F1/00—Details of amplifiers with only discharge tubes, only semiconductor devices or only unspecified devices as amplifying elements
- H03F1/26—Modifications of amplifiers to reduce influence of noise generated by amplifying elements
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- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03F—AMPLIFIERS
- H03F1/00—Details of amplifiers with only discharge tubes, only semiconductor devices or only unspecified devices as amplifying elements
- H03F1/30—Modifications of amplifiers to reduce influence of variations of temperature or supply voltage or other physical parameters
- H03F1/301—Modifications of amplifiers to reduce influence of variations of temperature or supply voltage or other physical parameters in MOSFET amplifiers
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- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03F—AMPLIFIERS
- H03F3/00—Amplifiers with only discharge tubes or only semiconductor devices as amplifying elements
- H03F3/68—Combinations of amplifiers, e.g. multi-channel amplifiers for stereophonics
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- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03F—AMPLIFIERS
- H03F2200/00—Indexing scheme relating to amplifiers
- H03F2200/294—Indexing scheme relating to amplifiers the amplifier being a low noise amplifier [LNA]
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Abstract
The invention discloses a self-feedback low noise amplifier applied to biopotential treatment, which comprises: input capacitance CinAmplifier A, feedback resistor R and feedback capacitor Cf(ii) a Wherein the amplifier A comprises a first stage amplifier A1And a second stage amplifier A2(ii) a The input capacitor CinIs connected to the input end VinAnd the first stage amplifier A1Between the input terminals of (1); the feedback resistor R is connected in parallel with the first-stage amplifier A1Between the input and output terminals; the feedback capacitor CfIs connected to the first stage amplifier A1And said second stage amplifier a2Between the output terminals of (a). The low-noise amplifier provided by the invention not only greatly improves the filter constant of the amplifier and realizes lower high-pass cut-off frequency, but also effectively reduces the size of the required feedback capacitor, reduces the power consumption, and simultaneously avoids the influence of the nonlinearity of the feedback resistor on the output signal by changing the connection mode of the feedback resistor.
Description
Technical Field
The invention belongs to the technical field of integrated circuits, and particularly relates to a self-feedback low-noise amplifier applied to biopotential processing.
Background
Under the wave of the mobile internet, wearable technology develops rapidly, and wearable medical equipment takes place. The wearable medical equipment is portable medical or health electronic equipment which can be directly worn on the body, senses and records human body information under the support of software, analyzes, regulates, intervenes and even treats diseases or maintains a health state, wherein accurate collection of the human body information is very important and concerns subsequent analysis and treatment, so that a biomedical chip for collecting the human body information becomes a key part of the wearable medical equipment. The most critical and important module in the whole biomedical chip is an analog front-end signal acquisition processing circuit, which is a critical circuit for connecting a human body, a sensor and a circuit system and is also a bridge for converting human body information into circuit signals, and a low-noise amplifier in the analog front-end circuit determines the important performances of the integrity, the accuracy, the signal-to-noise ratio, the distortion and the like of the acquired signals.
However, the low-noise amplifier needs to process the interference of the bioelectrode, such as direct-current offset voltage, power line 50/60Hz power frequency interference, human motion artifact and the like, so that the power consumption of the low-noise amplifier is very high; in addition, human biological signals are very weak, the frequency is extremely low, and the bandwidth is narrow, so that higher requirements are provided for a low-noise amplifier, and meanwhile, the wearable medical equipment is also very important in the aspect of reducing the area of a circuit chip, so that the design of the low-noise amplifier with low power consumption, high performance and low cost has important significance for the development of modern wearable medical equipment.
Disclosure of Invention
In order to solve the above problems in the prior art, the present invention provides a self-feedback low noise amplifier applied to biopotential processing. The technical problem to be solved by the invention is realized by the following technical scheme:
a self-feedback low noise amplifier for biopotential processing, comprising: input capacitance CinAmplifier A, feedback resistor R and feedback capacitor Cf(ii) a Wherein the amplifier A comprises a first stage amplifier A1And a second stage amplifier A2；
The input capacitor CinIs connected to the input end VinAnd the first stage amplifier A1Between the input terminals of (1);
the feedback resistor R is connected in parallel with the first-stage amplifier A1Between the input and output terminals;
the feedback capacitor CfIs connected to the first stage amplifier A1And said second stage amplifier a2Between the output terminals of (1);
the second stage amplifier A2Is connected to the first stage amplifier A1The output of the second stage amplifier A2Is connected with the output end Vout。
In bookIn one embodiment of the invention, the input capacitance CinComprising first input capacitors C of the same capacitanceinnAnd a second input capacitance CinpThe feedback resistors R comprise first feedback resistors R with the same resistance value1And a second feedback resistor R2Said feedback capacitance CfComprises a first feedback capacitor C with the same capacitance valuefnAnd a second feedback capacitor Cfp(ii) a Wherein the content of the first and second substances,
the first input capacitor CinnIs connected to the first input terminal VinnAnd the first stage amplifier A1Between the non-inverting input terminal of, the second input capacitance CinpIs connected to the second input terminal VinpAnd the first stage amplifier A1Between the inverting input terminals of;
the first feedback resistor R1Is connected in parallel with the first stage amplifier A1Non-inverting input terminal and second output terminal V ofoutp1And the second feedback resistance R2Is connected in parallel with the first stage amplifier A1And the first output terminal Voutn1To (c) to (d);
the first feedback capacitor CfnIs connected to the first stage amplifier A1And said second stage amplifier a2Second output terminal VoutpAnd the second feedback capacitor CfpIs connected to the first stage amplifier A1And said second stage amplifier a2First output terminal VoutnIn the meantime.
The invention has the beneficial effects that:
1. according to the invention, by changing the connection mode of the feedback resistor, the filter constant of the amplifier is greatly improved under the condition that the capacitance value of the feedback capacitor is not changed, and lower high-pass cut-off frequency is realized; a smaller feedback capacitor is used, so that the circuit area can be effectively saved, and the chip size is reduced;
2. according to the invention, by changing the connection mode of the feedback resistor, the influence caused by electrode detuning and amplifier internal detuning is effectively eliminated;
3. according to the invention, the linearity of the output signal of the circuit is improved by changing the connection mode of the feedback resistor;
4. the invention can work under the condition of 0.5V power supply voltage, and sets the input-stage direct-current working point without an additional bias circuit, thereby saving the power consumption of the system.
The present invention will be described in further detail with reference to the accompanying drawings and examples.
Drawings
FIG. 1 is a simplified block diagram of a self-feedback low noise amplifier for biopotential processing provided by embodiments of the present invention;
FIG. 2 is a schematic structural diagram of a self-feedback low noise amplifier applied to biopotential treatment according to an embodiment of the present invention;
fig. 3 is a schematic structural diagram of a conventional low noise amplifier according to an embodiment of the present invention.
FIG. 4 is a high-pass angular position produced by two amplifiers provided by embodiments of the present invention;
fig. 5 is a graph comparing output signals THD of two amplifiers according to an embodiment of the present invention.
Detailed Description
The present invention will be described in further detail with reference to specific examples, but the embodiments of the present invention are not limited thereto.
Example one
Referring to fig. 1, fig. 1 is a simplified block diagram of a self-feedback low noise amplifier applied to biopotential processing according to an embodiment of the present invention.
The invention provides a self-feedback low-noise amplifier applied to biopotential treatment, which comprises: input capacitance CinAmplifier A, feedback resistor R and feedback capacitor Cf(ii) a Wherein the amplifier A comprises a first stage amplifier A1And a second stage amplifier A2；
The input capacitor CinIs connected to the input end VinAnd the first stage amplifier A1Between the input terminals of (1);
the feedback resistor R is connected in parallel with the first-stage amplifier A1Is transported byBetween the input end and the output end;
the feedback capacitor CfIs connected to the first stage amplifier A1And said second stage amplifier a2Between the output terminals of (1);
the second stage amplifier A2Is connected to the first stage amplifier A1The output of the second stage amplifier A2Is connected with the output end Vout。
Since the DC electrode imbalance (50mV) is often present in the process of acquiring the biological signals, and the biological signals are often less than 1mV, the high gain amplifier applied to the biological signals is saturated, and useful biological signals cannot be acquired. Therefore, the invention adopts a capacitive coupling mode to obtain the input signal, effectively filters the direct current component of the input signal by utilizing the characteristic of the capacitor and avoids the interference of the imbalance of the direct current electrode to the amplifier. Biological signals are input into the capacitor CinIs input to the first stage amplifier.
In the present embodiment, the amplifier a is a common two-stage amplifier composed of transistors. In order to amplify the signal voltage without distortion, the transistor-based amplifier should have its operating point set by a bias circuit.
The first is that a feedback resistor is directly connected to an input node and an output node of the amplifier, so that a filter constant is generated as R × C, wherein R is a feedback resistance value and C is a capacitance value of a feedback capacitor. The second one is that one end of the feedback resistor is connected with the input node of the amplifier, and the other end is directly connected with VcmThe common mode level, the resulting filter constant is R C Av, where Av is the amplifier open loop gain, and this bias circuit increases the filter constant by a factor of Av, but any slight offset in the amplifier input leads to saturation of the amplifier output, causing amplifier failure.
In this embodiment, the feedback resistor R is connected in parallel with the first stage amplifier A1From the first stage amplifier output node V between the input and output terminals of2The bias voltage required by the input tube of the amplifier is obtained, and additional arrangement is avoidedThe bias circuit saves the power consumption of the system. The filter constant generated by the connection mode is R C Av1, wherein R is the resistance value of the feedback resistor, and C is the feedback capacitor CfAv1 is the first stage open loop gain of the amplifier.
Since the biological signals have low frequency and small amplitude, the high-pass cut-off frequency must be kept below 1Hz, which requires a very large filter constant for the amplifier. In order to realize a very large filter constant, a resistor having a very large resistance value is used. In this embodiment, the feedback resistor is a pseudo resistor with a very large resistance value, and may be formed by a PMOS transistor connected in a diode manner, and its actual impedance is about 100G Ω, so that it is ensured that low-frequency biological signals can be collected, and the influence caused by dc electrode offset is eliminated.
The embodiment adopts a feedback capacitor mode to set gain, adopts a feedback resistor with a super-large resistance value to set a direct current working point, and adopts the connection mode of the invention, thereby not only reducing the use of an external bias circuit, effectively reducing the power consumption and reducing the area of a circuit chip; and the ultra-large filter constant and the lower high-pass cut-off frequency are realized, and the influence caused by the mismatch of the input tube of the amplifier is effectively eliminated.
According to the traditional connection mode, the pseudo resistor with the super-large resistance value is connected at the output end, and due to the nonlinearity of the pseudo resistor, the linearity of an output signal can be reduced.
In this embodiment, the feedback resistor is connected to the input port of the amplifier and the output port of the first-stage amplifier, so that the amplitude of the signal passing through the feedback resistor is smaller, and the linearity of the output signal of the amplifier is improved.
Referring to fig. 2, fig. 2 is a schematic structural diagram of a self-feedback low noise amplifier applied to biopotential processing according to an embodiment of the present invention. Wherein, Vinp、VinnIs a double-ended input signal of an amplifier, CinnAnd CinpFirst and second input capacitors of the same specification, CfnAnd CfpA first feedback capacitor and a second feedback capacitor with the same specification, R1And R2Is a first feedback resistor and a second feedback resistor with the same specification on the feedback branch, Voutn1And Voutp1Two outputs of the first stage amplifier a1, respectively. VoutnAnd VoutpRespectively, the outputs of the second stage amplifiers. ST1 and ST2 are two-stage amplifiers used in the present invention.
Double-ended input signal terminal VinnAnd VinpRespectively through input capacitance CinnAnd CinpConnected with the non-inverting input terminal and the inverting input terminal of the first-stage amplifier.
Feedback resistor R1Connected in parallel with the non-inverting input end and the output negative end V of the first-stage amplifieroutp1Form a negative feedback branch; feedback resistor R2Connected in parallel with the inverting input terminal and the positive output terminal V of the first-stage amplifieroutn1And a second negative feedback branch is formed.
Feedback capacitance CfnConnected in parallel with the non-inverting input end of the first-stage amplifier and the output negative end V of the second-stage amplifieroutpForm a third feedback branch; feedback capacitance CfpConnected in parallel with the inverting input terminal of the first stage amplifier and the positive output terminal V of the second stage amplifieroutnAnd a fourth feedback branch is formed.
In the present embodiment, the differential signal V is inputtedinnAnd VinpRespectively through input capacitance CinnAnd CinpCoupled to the input of the amplifier. When passing through the amplifier, from CinAnd CfSet the precision gain, using CfAnd the high-pass cut-off frequency of the whole path is set together with the feedback resistor R, so that the amplification of a useful signal in a bandwidth is finally realized, and a direct current electrode offset signal which can cause the saturation of the amplifier is filtered.
Example two
In order to make the above advantages of the present invention more comprehensible, the following comparative analysis is performed on the effects of the present invention in conjunction with a conventional low noise amplifier.
Referring to fig. 3, fig. 3 is a schematic structural diagram of a conventional low noise amplifier according to an embodiment of the present invention.
In the present embodiment, an input capacitance C is providedinAnd a feedback capacitor CfThe feedback resistor is respectively 10pF and 100fF, the feedback resistor uses a pseudo resistor which is formed by connecting PMOS tubes and has an ultra-large resistance value, the actual impedance of the pseudo resistor is about 100G omega, and the same pseudo resistor is used for carrying out simulation experiment comparison on the low-noise amplifier adopting the traditional bias mode and the low-noise amplifier adopting the novel bias mode provided by the invention.
Referring to fig. 4, fig. 4 shows the high pass angle (i.e., high pass cutoff frequency) positions generated by two amplifiers according to the embodiment of the present invention. It can be seen that the high-pass angular position is reduced from 586mHz to 10mHz by merely changing the connection of the dummy resistors.
In addition, the THD (harmonic distortion) of the output signal is greatly improved by changing the connection mode. Referring to fig. 5, fig. 5 is a THD comparison graph of two amplifier output signals according to an embodiment of the present invention. In the traditional mode, a pseudo resistor is directly connected with a signal, and the change of an output signal can cause the resistance value of the pseudo resistor to change, so that the high-pass angular position changes, and the THD of the signal at a low frequency is reduced. The connection mode provided by the invention connects the pseudo resistor with the first-stage output point, and reduces the influence of the pseudo resistor on the output signal to the greatest extent on the basis of ensuring that the self maladjustment of the amplifier can be eliminated.
The self-feedback low-noise amplifier applied to biopotential treatment provided by the invention not only greatly improves the filter constant of the amplifier and realizes lower high-pass cut-off frequency by changing the connection mode of the feedback resistor, but also effectively reduces the size of the required feedback capacitor, reduces the power consumption, and simultaneously avoids the influence of the nonlinearity of the feedback resistor on the output signal.
The foregoing is a more detailed description of the invention in connection with specific preferred embodiments and it is not intended that the invention be limited to these specific details. For those skilled in the art to which the invention pertains, several simple deductions or substitutions can be made without departing from the spirit of the invention, and all shall be considered as belonging to the protection scope of the invention.
Claims (1)
1. A self-feedback low noise amplifier for biopotential processing, comprising: input capacitance CinAmplifier A, feedback resistor R and feedback capacitor Cf(ii) a Wherein the amplifier A comprises a first stage amplifier A1And a second stage amplifier A2；
The input capacitor CinIs connected to the input end VinAnd the first stage amplifier A1Between the input terminals of (1); wherein the input capacitor CinComprising first input capacitors C of the same capacitanceinnAnd a second input capacitance CinpSaid first input capacitance CinnIs connected to the first input terminal VinnAnd the first stage amplifier A1Between the non-inverting input terminal of, the second input capacitance CinpIs connected to the second input terminal VinpAnd the first stage amplifier A1Between the inverting input terminals of;
the feedback resistor R is connected in parallel with the first-stage amplifier A1Between the input and output terminals; the feedback resistor R comprises a first feedback resistor R with the same resistance value1And a second feedback resistor R2The first feedback resistor R1Is connected in parallel with the first stage amplifier A1And said first stage amplifier a1Second output terminal Voutp1And the second feedback resistance R2Is connected in parallel with the first stage amplifier A1And said first stage amplifier a1First output terminal Voutn1To (c) to (d); the feedback capacitor CfIs connected to the first stage amplifier A1And said second stage amplifier a2Between the output terminals of (1); wherein the feedback capacitor CfComprises a first feedback capacitor C with the same capacitance valuefnAnd a second feedback capacitor CfpSaid first feedback capacitor CfnIs connected to the first stage amplifier A1And said second stage amplifier a2Second output terminal VoutpThe second inverse ofFeed capacitor CfpIs connected to the first stage amplifier A1And said second stage amplifier a2First output terminal VoutnTo (c) to (d);
the second stage amplifier A2Is connected to the first stage amplifier A1The output of the second stage amplifier A2Is connected with the output end Vout。
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| US7002409B1 (en) * | 2004-02-11 | 2006-02-21 | Marvell International Ltd. | Compensation circuit for amplifiers having multiple stages |
| CN101005271A (en) * | 2006-01-18 | 2007-07-25 | 马维尔国际贸易有限公司 | Nested transimpedance amplifier |
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