Analog-digital converter and signal processing system

A signal processing system, comprising:

• an analog-digital (AD) converter configured to convert analog signals from an analog signal processing system into digital signals, wherein
• the AD converter includes
• a plurality of cascade-connected analog-digital (AD) conversion stages configured to generate digital data having a value corresponding to a relationship between two analog signals being input and amplify two analog residual signals with a first amplifier and a second amplifier respectively with gain to be controlled to output the signals, and
• a gain control part configured to monitor the output signals of the first amplifier and the second amplifier to control gain of the first amplifier and the second amplifier on the basis of a monitoring result,
• the first amplifier and the second amplifier
• are formed of open-loop amplifiers, and
• the gain control part
• takes out amplitude information of the output signals of the first amplifier and the second amplifier in at least one of the AD conversion stages and performs gain control so that amplitude of the analog signals being output from the stage converges on setting amplitude being set.