Variable quantization adc for image sensors

A method for generating a sequence of reference voltages, comprising:

• receiving a sequence of clock signals;
• and
• on each clock signal:
• reading a plurality of control words from a memory, each one of the plurality of control words corresponding to a different one of a plurality of capacitor banks;
• sending or not sending a control and reset signal to each of the plurality of capacitor banks based on the content of a corresponding control word;
• controlling a plurality of switches at each of the plurality of capacitor banks, each of the switches being associated with a capacitor and controlling one of a plurality of voltage sources coupled to one plate of the capacitor, to produce a bank output voltage;
• and
• summing each bank output voltage to produce a master output voltage.

An imaging system comprising:

• a pixel array;
• and
• an analog to digital (A/D) converter circuit configured to receive analog signals from the pixel array and to convert the analog signals to digital signals with a variable-bit level of quantization, the A/D converter circuit comprising:
• a linear A/D converter configured to produce intermediate values from the analog signals, the linear A/D converter comprising a ramp generator;
• and
• a processing circuit configured to remap the intermediate values produced by the linear A/D converter using a mapping table.

A method for converting an analog signal to a digital word, comprising:

• measuring a magnitude of the analog signal;
• mapping the magnitude to a digital word with a first and second transfer function only, wherein:
• if the magnitude is less than a predetermined threshold, mapping the magnitude to the digital word exclusively with the first transfer function,
• if the magnitude is at least equal to the predetermined threshold, mapping the magnitude to the digital word exclusively with the second transfer function,
• the first transfer function is not included in the second transfer function, and
• the second transfer function is not included in the first transfer function.

A method for converting an analog signal to a digital word, comprising:

• measuring a magnitude of the analog signal;
• if the magnitude is not greater than a predetermined threshold, mapping the magnitude to a digital word in accordance with a first transfer function;
• and
• if the magnitude is at least equal to the predetermined threshold, mapping the magnitude to the digital word in accordance with a second transfer function,
• wherein:
• the first transfer function maps each magnitude below the predetermined threshold to a corresponding reference signal in a linear manner, and
• the second transfer function maps a set of non-sequential and increasing magnitudes each at least equal to the predetermined threshold to corresponding reference signals in a linear manner.

A method for operating an imaging system, comprising:

• receiving an analog pixel signal from a pixel;
• converting the analog pixel signal into a digital word, wherein the converting comprises:
• measuring a magnitude of the analog signal;
• mapping the magnitude to a digital word with a first and second transfer function only, wherein:
• if the magnitude is less than a predetermined threshold, mapping the magnitude to the digital word exclusively with the first transfer function,
• if the magnitude is at least equal to the predetermined threshold, mapping the magnitude to the digital word exclusively with the second transfer function,
• the first transfer function is not included in the second transfer function, and
• the second transfer function is not included in the first transfer function.

A method for operating an imaging system, comprising:

• receiving an analog pixel signal from a pixel;
• converting the analog pixel signal into a digital word, wherein the converting comprises:
• measuring a magnitude of the analog signal;
• if the magnitude is not greater than a predetermined threshold, mapping the magnitude to a digital word in accordance with a first transfer function;
• and
• if the magnitude is at least equal to the predetermined threshold, mapping the magnitude to the digital word in accordance with a second transfer function,
• wherein:
• the first transfer function maps each magnitude below the predetermined threshold to a corresponding reference signal in a linear manner, and
• the second transfer function maps a set of non-sequential and increasing magnitudes each at least equal to the predetermined threshold to corresponding reference signals in a linear manner.