Signal receiving apparatus and programmable gain amplifier having mode-switching mechanism

A signal receiving apparatus comprising:

• a programmable gain amplifier comprising:
• an operational amplifier comprising a first input terminal, a second input terminal and an output terminal, wherein the second input terminal is electronically coupled to a ground terminal, and the output terminal is configured to generate an output signal;
• a variable resistor and a first switch electrically coupled in series between a first terminal and a second terminal, wherein the second terminal is electronically coupled to the first input terminal;
• a first variable capacitor and a second switch electrically coupled in series between the first terminal and the second terminal;
• a second variable capacitor and a third switch electrically coupled in series between the first terminal and the ground terminal;
• a low-pass resistor and a low-pass capacitor electrically coupled in parallel between the first input terminal and the output terminal;
• and
• an input resistor electronically coupled to a signal input terminal and the first terminal and configured to receive an input signal from the signal input terminal;
• an analog-to-digital conversion circuit configured to perform analog-to-digital conversion on the output signal;
• and
• a digital signal processing circuit electronically coupled to the output terminal through the analog-to-digital conversion circuit and configured to receive the output signal after the analog-to-digital conversion is performed;
• wherein the digital signal processing circuit is further configured to generate a set of mode switching signals such that the first switch, the second switch and the third switch are configured to be switched according to the set of mode switching signals to each form a path or an open-circuit.