Calibration circuit and associated method

A method for obtaining a calibrated output signal from an input signal prior to amplification by a gain amplifier comprising:

• converting the amplified signal to a digital signal;
• applying an inverse gain factor to a signal derived from said digital signal to obtain a digital offset signal;
• converting said digital offset signal to an analogue offset signal;
• and
• using said analogue offset signal to apply an offset to said input signal prior to amplification, thereby to define a feedback loop.

An image capturing system comprising:

• an imaging sensor for producing an analogue input signal,
• a signal conditioning circuit which comprises an analogue gain amplifier comprising a first input for receiving said analogue input signal, said analogue gain amplifier being configured to apply a gain to said input signal,
• a signal conversion circuit which comprises an analogue to digital converter for converting said input signal to digital form after amplification by said gain amplifier, wherein said signal conversion circuit generates, at an output, a calibrated digital signal representing an analogue input signal received from said imaging sensor via said signal conversion circuit, wherein said image capturing system further comprises calibration circuitry for calibrating said input signal, said calibration circuitry comprising:
• a correction circuit for receiving a signal derived from the output of the analogue to digital converter and outputting a digital offset signal;
• and
• a digital to analogue converter for receiving said digital offset signal and feeding a corresponding analogue offset signal back to the input of said gain amplifier, such that said correction circuit and said digital to analogue converter form a feedback loop applying an offset to said input signal, wherein said correction circuit includes an inverse gain circuit for applying an inverse gain to a signal within said correction circuit prior to said digital to analogue converter, said inverse gain being applied so as to establish a combined gain response applied around said feedback loop within predetermined bounds.