Patent ID: 8767988

Claim:
An analog front circuit for a medical device, comprising an automatic gain control loop ( 10 ) and a 2-order-3-bit-quantization Sigma-Delta analog-to-digital converter ( 20 ), wherein: the automatic gain control loop ( 10 ) is configured to implement automatic control of loop gain and output an analog signal to the 2-order-3-bit-quantization Sigma-Delta analog-to-digital converter ( 20 ); the 2-order-3-bit-quantization Sigma-Delta analog-to-digital converter ( 20 ) is configured to convert the analog signal output from the automatic gain control loop into a digital code and output the digital code to a DSP for processing; and the automatic gain control loop ( 10 ) comprises a variable-gain amplifier ( 100 ), a fixed-gain amplifier ( 101 ), a first buffer and a second buffer ( 110 , 111 ), a first comparator, a second comparator, and a third comparator ( 120 , 121 , 122 ), and a peak statistics determination logic and gain control logic module ( 130 ), wherein: the variable-gain amplifier ( 100 ) in the automatic gain control loop ( 10 ) of the analog front circuit amplifies or attenuates an output signal from a microphone and the fixed-gain amplifier ( 101 ) amplifies a noise signal; an analog signal output from the variable-gain amplifier ( 100 ) is buffered by the first buffer ( 110 ) and then compared with a peak threshold voltage and an activation threshold voltage by the first comparator and the second comparator ( 120 , 121 ), respectively, to generate a respective 1-bit digital code comparison result, which is output to the peak statistics determination logic and gain control logic module ( 130 ); an analog signal output from the fixed-gain amplifier ( 101 ) is buffered by the second buffer ( 111 ) and then compared with a noise threshold voltage by a third comparator ( 122 ) to generate a 1-bit digital code comparison result, which is output to the peak statistics determination logic and gain control logic module ( 130 ); and the peak statistics determination logic and gain control logic module ( 130 ) performs statistics operation and determination on the digital code comparator results output from the first comparator, the second comparator, and the third comparator ( 120 , 121 , 122 ) to output a 21-bit digital code control signal to the variable-gain amplifier ( 100 ) to perform automatic loop gain control.