Signal amplifying circuit and signal processing system and analog-to-digital converting system comprising the same

A signal processing system, comprising:

• an input amplifying stage;
• a low-pass filter, configured to filter an output of the input amplifying stage;
• and
• a delta-sigma modulator, comprising:
• an integration stage, configured to integrate an output of the low-pass filter, and comprising a plurality of stages of integrator;
• an adder, configured to add the output of the low-pass filter and an output of each stage of integrator;
• a quantizer, configured to generate a digital signal according to an output of the adder;
• and
• a feedback circuit, configured to feedback the digital signal to the integration stage,
• wherein one or more of the input amplifying stage, the integration stage and the adder comprise a signal amplifying circuit, and the signal amplifying circuit comprises:
• an amplifier, configured to generate a first output and a second output, so as to correspondingly form the output of the input amplifying stage, the output of each stage of integrator and the output of the adder;
• and
• a common mode feedback circuit, configured to receive the first output and the second output, configured to control an output common mode voltage of the first output and the second output to be substantially identical to a first reference voltage, and comprising:
• an output common mode voltage detection circuit, configured to generate a first control signal and a second control signal according to a value of the output common mode voltage;
• a pull-up circuit with a first conduction degree controlled by the first control signal, configured to control the output common mode voltage to be positively correlated with the first conduction degree;
• and
• a pull-down circuit with a second conduction degree controlled by the second control signal, configured to control the output common mode voltage to be negatively correlated with the second conduction degree.

An analog-to-digital converting system, comprising:

• an input amplifying stage;
• a low-pass filter, configured to filter an output of the input amplifying stage;
• and
• an analog-to-digital converter, configured to process an output of the low-pass filter to generate a digital signal,
• wherein the input amplifying stage comprises a signal amplifying circuit, and the signal amplifying circuit comprises:
• an amplifier, configured to generate a first output and a second output to form the output of the input amplifying stage;
• and
• a common mode feedback circuit, configured to receive the first output and the second output, configured to control an output common mode voltage of the first output and the second output to be substantially identical to a first reference voltage, and comprising:
• an output common mode voltage detection circuit, configured to generate a first control signal and a second control signal according to a value of the output common mode voltage;
• a pull-up circuit with a first conduction degree controlled by the first control signal, and configured to control the output common mode voltage to be positively correlated with the first conduction degree;
• and
• a pull-down circuit with a second conduction degree controlled by the second control signal, and configured to control the output common mode voltage to be negatively correlated with the second conduction degree.