Self-adaptive bias input stage applied to current balance instrument amplifier

Abstract

The invention discloses an adaptive bias input stage applied to a current balance instrumentation amplifier. The circuit mainly comprises an input buffer, a minimum current selector and a bias control circuit. The minimum current selector is used for detecting the smaller value of the current of the two branches to ensure that the bias current is always kept at a proper level; when a small signal is input, the bias control circuit automatically reduces the bias current of the input stage, so that the power consumption is reduced; when a large signal is input, the bias control circuit properly increases the input stage bias current according to the magnitude of the input voltage so as to enhance the linearity. The strategy realizes balance between power consumption and performance; compared with the prior art, the self-adaptive bias input stage has the advantages of wide input range, high linearity, low power consumption, high energy efficiency and high response speed.

Description

Technical Field

[0001] The present invention belongs to the technical field of instrumentation amplifiers, and more specifically, relates to an adaptive bias input stage applied to a current balance instrumentation amplifier. Background Art

[0002] In application scenarios such as high-precision industrial control, medical instruments, and biological signal acquisition, instrumentation amplifiers are the core components for processing and amplifying weak signals, and are widely used in the signal link from sensor readout to data acquisition systems. These fields usually pose extremely high requirements for signal accuracy, reliability, as well as device efficiency and stability. Therefore, strict specifications are also imposed on the performance indicators of instrumentation amplifiers. For example, in industrial control systems, instrumentation amplifiers are often used to collect 4 to 20 mA current signals output by transmitters, and this process poses strict requirements on the common-mode rejection ratio and input range of the instrumentation amplifier; in medical devices, instrumentation amplifiers are widely used in the acquisition and amplification of biological signals such as electrocardiogram, electroencephalogram, and electromyogram. Such signals are often weak in amplitude, usually in the microvolt to millivolt level, posing relatively high requirements for the accuracy and energy efficiency of the instrumentation amplifier.

[0003] In the above scenarios, the importance of instrumentation amplifiers has become increasingly prominent. Among them, current balance instrumentation amplifiers achieve high common-mode rejection ratio, high energy efficiency, and high input impedance by virtue of their "open-loop" architecture and the characteristic of "converting the input voltage into current for transmission", as Figure 1 shown. Among them, the input stage of the current balance instrumentation amplifier consists of two inverting voltage followers and an input stage resistor R in formed. The input voltage is applied across R in through the follower, causing a current proportional to the input voltage to be generated across R in , and then this current is transmitted to the output stage, as Figure 2 shown.

[0004] The maximum value of the input differential voltage of the current balance instrumentation amplifier is the product of the input stage resistor R in and the input stage bias currents I s1 , I s2 (I s1 = I s2 ). To reduce the equivalent input noise, R in usually needs to be selected with a relatively small resistance value. Therefore, in order to achieve a sufficient input range, a relatively large bias current is required. Especially in high-voltage application scenarios, instrumentation amplifiers usually require an input range of more than ±10V, which will correspond to static power consumption in the milliampere level. This is essentially because the input stage of the current balance instrumentation amplifier adopts a class-A bias architecture, and the bias currents I s1 , I s2It is always constant, resulting in the need to maintain a high static current in the case of a wide input range, significantly reducing the energy efficiency. Even so, as the amplitude of the input signal increases, the performance of the input stage of the current balance instrumentation amplifier will gradually deteriorate, manifested as a decrease in linearity and an increase in distortion, limiting the use of the instrumentation amplifier in precision applications. This restricts the further development of traditional current balance instrumentation amplifiers in the fields of low power consumption and high precision.

[0005] Generally speaking, although the existing current balance instrumentation amplifiers have advantages in terms of high common-mode rejection ratio and high input impedance, there are still significant challenges in the balance of power consumption, input range, and linearity. It is urgent to break through through new design methods and technical means to meet the requirements of low power consumption, high linearity, and wide input range instrumentation amplifiers in industries, medical care, and other high-precision fields. Summary of the Invention

[0006] Aiming at the deficiencies of the above-mentioned existing technologies, the purpose of the present invention is to provide a new class AB input stage based on adaptive biasing. The adaptive biasing dynamically adjusts the bias current of the input stage, enabling the amplifier to achieve high energy efficiency operation at different input voltages, thereby significantly improving the input range and linearity. Especially in high-voltage industrial applications, the present invention provides an efficient and flexible solution for current balance instrumentation amplifiers.

[0007] The technical solution of the present invention is specifically introduced as follows.

[0008] The present invention provides an adaptive biasing input stage applied to a current balance instrumentation amplifier, which includes an input buffer, a minimum current selector, and a bias control circuit; wherein:

[0009] Input buffer: It is composed of two symmetrical flip voltage followers and an input resistor R in and realizes the conversion from the input voltage V in to the branch currents I in and I in by applying the input voltage V p across the resistor R n after passing through the followers; the two flip voltage followers respectively provide the basic bias currents I b1 and I b2 , as well as the bias currents I s1 and I s2 through symmetrical current sources, and the bias currents I s1 and I s2 are dynamically adjusted by the bias control circuit at the same time;

[0010] Minimum current selector: It is used to detect the two branch currents I p and I nThe smaller value, the minimum detected current I min is used as the input of the bias control circuit;

[0011] Bias control circuit: Set the quiescent current I through a current source b , and compare the minimum current I min with the quiescent current I b to generate a control voltage V b for dynamically adjusting the bias current I s1 , I s2 to optimize the operating state of the input stage.

[0012] In the present invention, in the minimum current selector, the output current is determined by the higher value of the gate voltages of two series-connected transistors, achieving the effect of minimum current selection. At the same time, the two paths of minimum current are output after exchanging the gate positions to ensure symmetry, and the remaining cascode transistor is used to ensure the matching between the sum branch current.

[0013] In the present invention, in the bias control circuit, two transistors form a current mirror, and the minimum current I min is compared with the quiescent current I b through the current mirror to generate a control voltage V b .

[0014] Above, compared with the traditional fixed bias technology, the adaptive bias technology of the present invention has the following remarkable advantages and beneficial effects:

[0015] ① Wide input range and high linearity: By adjusting the bias current of the input stage in real time, the present invention can maintain the linearity of the input stage under large differential input voltage conditions. The minimum current selector detects the smaller branch current in the differential pair and feeds it back to the bias control circuit to dynamically adjust the bias current, thereby achieving a wider input range.

[0016] ② Low power consumption and high energy efficiency: When a small signal is input, the adaptive bias technology will automatically reduce the bias current of the input stage, thereby reducing the static power consumption. Different from the traditional class-A input stage that needs to maintain a high quiescent current, this technology can flexibly adjust the power consumption according to the size of the input signal, achieving efficient power management, and is particularly suitable for industrial applications with high requirements for energy efficiency.

[0017] ③ High response speed: Compared with the traditional class-A input stage, the present invention, due to the introduction of the minimum current selector and the bias control circuit, modifies the input stage loop from a two-stage loop to a three-stage loop. Although the compensation difficulty is increased, it can still maintain the same high response speed as the traditional class-A input stage. In summary, the present invention significantly improves the input range, linearity, and energy efficiency of the amplifier by adjusting the input stage bias current in real time through the adaptive bias technology, making it have outstanding competitive advantages in the fields of high precision and low power consumption. Description of the Drawings

[0018] Figure 1 Block diagram of a current - balanced instrumentation amplifier

[0019] Figure 2 Schematic diagram of the input stage of a current - balanced instrumentation amplifier

[0020] Figure 3 Schematic diagram of the input stage of a current - balanced instrumentation amplifier based on adaptive biasing

[0021] Figure 4 DC simulation results of the input - stage bias current

[0022] Figure 5 Linearity test results

[0023] Figure 6 Input - stage loop analysis Detailed Implementation Manner

[0024] The technical solution of the present invention will be introduced in detail below in conjunction with the drawings and embodiments

[0025] The present invention provides an adaptive - bias input stage applied to a current - balanced instrumentation amplifier, which detects the minimum current in two paths of currents in the input stage and adjusts the bias current in real - time, so that the minimum current is equal to the set value, while the maximum current will continuously increase as the input voltage increases, ensuring that the input stage still has good linearity and low power consumption under a large differential input voltage. The adaptive - bias technology realizes efficient operation in different working states by adjusting the bias current of the input stage of the current - balanced instrumentation amplifier in real - time

[0026] As Figure 3 shown, the adaptive - bias module mainly includes the following three core parts

[0027] Input buffer: It consists of two unity - gain voltage followers and an input resistor R in and is composed of transistors M inp , M1, M3, M5, current sources I b1 , I s1 , and the second unity - gain voltage follower is composed of transistors M inn , M2, M4, M6, current sources I b2 , I s2 . By applying the input voltage V in across the resistor after passing through the follower, the conversion from the input voltage V in to the branch currents I p , I n is achieved

[0028] Minimum - current selector: Consisting of transistors M9, M10 , M 11 , M 12 , M 13 constitutes a circuit for detecting the smaller value of two branch currents I p and I n . The minimum current I min is used as the input to the bias control circuit;

[0029] Bias control circuit: It consists of transistors M7 and M8, and current sources I b and I min . The bias control circuit compares the minimum current I min with the static current I b . The comparison result V b is used to dynamically adjust the bias currents I s1 and I s2 to optimize the operating state of the input stage.

[0030] Its working process is as follows: The differential input signals V inp and V inn are input into the differential pair. The initial bias current I s is provided by the bias control circuit, and the bias current I s = (I p + I n ) / 2. When the input signal is small, the branch currents I p and I n are close to balance. When the amplitude of the input signal increases, the two branch currents I p and I n become asymmetric. One branch current decreases while the other increases. Therefore, the minimum current I min detected by the minimum current selector decreases. When it is detected that the minimum current I min decreases, the comparison result V b of the bias control circuit increases, which in turn causes the bias current I s to increase, thereby compensating for the decrease in the minimum current I min and preventing the input stage from malfunctioning due to the decrease in the minimum current I min . Conversely, when the input signal decreases, the bias circuit decreases I s to reduce the static power consumption. The relationship between the bias current I s , the branch currents I p and I n and the input voltage V in is as shown in Figure 4 .

[0031] The core idea of adaptive biasing is to optimize the power consumption of the input stage by monitoring the current changes in the differential input pair in real time. Through this dynamic adjustment mechanism, the input stage can achieve low-power operation under small-signal inputs and provide sufficient input range and linearity under large-signal inputs. This mechanism effectively achieves an optimized balance between power consumption and performance, avoiding the problem of high static power consumption in traditional fixed-biasing designs.

[0032] From the test results Figure 5 it can be seen that at a power supply voltage of 36V, the total harmonic distortion of the instrumentation amplifier can be less than 0.34% under an input voltage of ±24V. This indicates that the present invention can maintain the linearity of the input stage under large differential input voltage conditions. This effectively solves the problem of the linearity degradation of the input stage with traditional fixed biasing under high input signal amplitudes.

[0033] Compared with the traditional class-A input stage, due to the introduction of the minimum current selector and the bias control circuit, the present invention modifies the input stage loop from a two-stage loop to a three-stage loop. Although it increases the compensation difficulty, it can still maintain the same high response speed as the traditional class-A input stage. The specific analysis is as Figure 6 shown. The adaptive-biased input stage proposed by the present invention can be divided into transconductance stages G m1 , G m2f , G m2 , G m3 , and compensation capacitors C m1 , C m2 . Among them, the transconductance stage G m1 is composed of transistors M3, M5, and current source I b1 , the transconductance stage G m2f is composed of transistors M1, M in , and resistor R in , the transconductance stage G m2 is composed of transistors M7, M8, M9, and current source I b , and the transconductance stage G m3 is composed of transistor M 14 . The compensation capacitors C m1 , C m2 are used to stabilize the three-stage loop and avoid oscillations caused by insufficient phase margin. The closed-loop bandwidth of the adaptive-biased input stage is determined by the open-loop gain-bandwidth product, and the open-loop gain-bandwidth product is determined by the transconductance stage G m1 and the compensation capacitor C m1 . Since these two structures are inherent in the traditional class-A input stage, it can still maintain the same high response speed as the traditional class-A input stage.

[0034] When a small signal is input, the adaptive bias technology automatically reduces the bias current of the input stage, thereby reducing the static power consumption. Different from the traditional class-A input stage that needs to maintain a high static current, the present invention can flexibly adjust the power consumption according to the size of the input signal, achieving efficient power management, and is particularly suitable for industrial applications with high energy efficiency requirements.

[0035] In summary, the adaptive bias technology significantly improves the input range, linearity, and energy efficiency of the amplifier, giving it outstanding competitive advantages in the fields of high precision and low power consumption.

[0036] The adaptive bias proposed by the present invention has wide applicability. This technology generated based on the minimum current selector can be applied to other circuits besides high-voltage current-balanced instrumentation amplifiers, such as low-voltage current-balanced instrumentation amplifiers, and other front-end circuits.

[0037] The solution of combining the fixed bias and the adjustable current source of the present invention can adopt the method of combining the fixed bias circuit with the multi-stage adjustable current source. Add a control module in the input stage to trigger the change of the bias current through an external signal or a preset threshold. Although this method is less flexible than the adaptive bias, it can still meet the input range and linearity requirements of different input signals through multi-stage current adjustment.

Claims

1. An adaptive bias input stage applied to a current balanced instrumentation amplifier, characterized in that, It includes an input buffer, a minimum current selector, and a bias control circuit; among which: Input buffer: It consists of two symmetric inverting voltage followers and an input resistor R in and realizes the conversion from the input voltage V in to the branch currents I in and I in by applying the input voltage V p across the resistor R n after passing through the followers; The two inverting voltage followers are respectively provided with the base bias currents I b1 and I b2 , as well as the bias currents I s1 and I s2 by symmetric current sources, and the bias currents I s1 and I s2 are dynamically regulated by the bias control circuit at the same time; Minimum current selector: It is used to detect the smaller value of the two branch currents I p and I n . The detected minimum current I min is used as the input of the bias control circuit; Bias control circuit: Set the quiescent current I through a current source b , compare the minimum current I min with the quiescent current I b to generate a control voltage V b for dynamically adjusting the bias currents I s1 and I s2 to optimize the operating state of the input stage.

2. The adaptive bias input stage according to claim 1, wherein In the minimum current selector, the output current is determined by the higher value of the gate voltages of two series-connected transistors, achieving the effect of minimum current selection. At the same time, the two minimum currents exchange their gate positions and are respectively output to ensure symmetry, and the remaining cascode transistor is used to ensure the matching between the sum branch currents.

3. The adaptive bias input stage according to claim 1, wherein In the bias control circuit, two transistors form a current mirror, and the minimum current I min is compared with the static current I b through the current mirror to generate a control voltage V b .

Images