CN114531120A

CN114531120A - High-performance 8-channel bioelectric signal instrument amplifier

Info

Publication number: CN114531120A
Application number: CN202210001186.7A
Authority: CN
Inventors: 李强; 谭博睿
Original assignee: University of Electronic Science and Technology of China
Current assignee: University of Electronic Science and Technology of China
Priority date: 2022-01-04
Filing date: 2022-01-04
Publication date: 2022-05-24

Abstract

The invention relates to a high-performance 8-channel bioelectricity signal instrument amplifier, which still maintains excellent common-mode rejection ratio by using an improved time division multiplexing technology under a multi-channel structure using reference end multiplexing. Meanwhile, on each single-channel layer, the T-shaped capacitor network structure is used on the gain negative feedback loop and the positive feedback loop, and on the basis of not reducing the gain, the input capacitance value is greatly reduced, so that output waveform burrs introduced by a chopping technology are greatly reduced, and the requirement on a low-pass filter in the analog front end of biological signal acquisition is reduced. Meanwhile, the invention has the characteristics of low power consumption, low noise, high input impedance and the like.

Description

High-performance 8-channel bioelectric signal instrument amplifier

Technical Field

The invention relates to a high-performance 8-channel bioelectric signal instrument amplifier which is used for collecting and amplifying a bioelectric signal in an analog front end for collecting the bioelectric signal.

Background

The environment for collecting the bioelectric signals generally faces a large amount of common-mode interference, which requires that an instrumentation amplifier used for collecting the bioelectric signals must have a high common-mode rejection ratio, medical diagnosis requires that the collection of the bioelectric signals must be performed in a multi-channel mode to ensure the reliability of the signals, and meanwhile, the chopping technology is widely applied to the bioelectric signal instrumentation amplifier to improve the common-mode rejection ratio and reduce input reference noise. In order to reduce the electrode overhead, a multi-channel structure is usually realized by sharing a reference terminal for all single channels, which brings the problem of system mismatch and reduces the common mode rejection ratio in a multi-channel operating mode, the use of the chopping technology also brings some negative effects, generally, the speed of a bioelectrical signal instrumentation amplifier is slow, and a certain time is required for reaction under each chopping action, so that some "spikes" appear on an output signal, and the spikes must be filtered by a low-pass filter, which increases additional overhead.

Disclosure of Invention

A high-performance 8-channel bioelectrical signal instrument amplifier adopts a classical multi-channel structure of a multiplexing reference electrode and uses an improved time division multiplexing technology on the basis, so that the system mismatch caused by electrode multiplexing can be reduced, and the common-mode rejection ratio of the amplifier is improved. On a single-channel level, a chopping technology is used for reducing input reference noise of an amplifier and simultaneously improving a common-mode rejection ratio, a positive feedback loop technology is used, a pre-charging technology is used for improving input differential-mode impedance, a direct current rejection loop (DC voltage loop) is introduced for eliminating electrode imbalance, a large-time-constant integrator in the loop is realized by a duty-cycle resistor technology, and meanwhile, a T-type capacitor network technology is used for greatly reducing output wave-type burrs and simultaneously improving input common-mode impedance to a certain degree under the condition of not reducing gain.

Drawings

FIG. 1 is a schematic diagram of an 8-channel bioelectric signal instrumentation amplifier.

Fig. 2 is a schematic diagram of a specific circuit structure of a single-channel amplifier.

FIG. 3 is a timing diagram of the specific circuit of the 8-channel bioelectrical signal instrumentation amplifier.

Detailed Description

The invention is described in detail below with reference to the figures and the specific embodiments.

As shown in fig. 1, the inverting input of each channel is connected to the input and output of the buffer through two switches controlled by a pair of non-overlapping clocks, while the input of the buffer is directly connected to the reference input, and the non-inverting input of each channel is independent of the signal input. In any time period, only one of the switches controlled by the signals CLK1-CLK8 is closed, and all the other switches are closed, so that the input impedance seen from the signal input end of the channel is equal to the input impedance seen from the reference end, and system mismatch is avoided. On the other hand, the switch controlled by the reverse clock ensures that the reverse input ends of other channels track the input signal of the reference end through the buffer, so that the time required by signal reestablishment is greatly reduced when the channels are switched. Finally, the signals of the channels are output through a multi-channel check device.

On the single-channel level, as shown in fig. 2, each channel is a capacitive coupling type instrumentation amplifier with chopping, and both the gain negative feedback loop and the positive feedback loop of the amplifier use a T-type capacitor network structure, i.e., a capacitor is used to connect the two paths of the differential feedback loop to form two T-type networks in a forward and backward direction. The output spike caused by chopping is mainly because each transconductance stage in the amplifier is relatively slow, particularly because the transconductance stage Gm3 on the DC voltage loop is not timely responsive when a chopping switch performs switching, and simultaneously, the voltage at two ends of a capacitor cannot change instantaneously, at the moment, the input capacitor and the load capacitor of the whole amplifier are subjected to voltage division, so that the output spike occurs, and the spike even becomes a ripple form with unacceptable amplitude because the Gm3 is too slow. The use of a T-type capacitor network will greatly reduce the value of the input capacitance while maintaining the gain, thereby greatly reducing this capacitive voltage division effect.

The pre-charging technique is at the input chopper f_CH1The input chopper is provided with a dead zone, and the pre-charging branch pre-charges the input capacitor through the buffer in the dead zone time, so that the charge extracted from a signal source after the input chopper starts working is reduced, and the differential input resistance is improved. The buffer is controlled by the control signal to work only in a dead zone, so that the power consumption is reduced, and meanwhile, the low-frequency error at the input end of the buffer is modulated by the other pair of choppers fL. R in DC suppression loop_INTFormed by a duty-cycle technique, consisting of a smaller resistance in combination with a conductionThe very short time switch constitutes an equivalent large resistance, R to prevent aliasing_AAnd C_AAn anti-aliasing filter is constructed.

Fig. 3 shows the operation timing sequence of the whole 8-channel bioelectric signal instrumentation amplifier. In which the main chopper f_CHSet to 10KHZ, f_LAt 5KHZ, one on-time of the channel switch clock is set to complete 4 primary chops. f. of_CH1Is set to 2.5 us. One pulse length of the DCR is set to 500 ps.

Claims

1. A high-performance 8-channel bioelectric signal instrumentation amplifier is characterized by low power consumption, low noise, high common-mode rejection ratio and high input common-mode/differential-mode impedance.

2. The high-performance 8-channel bioelectrical signal instrumentation amplifier according to claim 1, wherein an improved time division multiplexing technique is adopted at the multi-channel level; in a single-channel layer, a T-type capacitor network technology is adopted, and output wave type burrs introduced by chopping waves are greatly reduced under the condition of not reducing gains.