Cascoded comparator with dynamic biasing for column parallel single slope ADCs
Aspects of the invention may comprise receiving a first input signal and a second input signal via respective first and second input transistors. A biasing signal, generated by a cascode bias generator, that tracks the first input signal, where the biasing signal has a fixed offset with respect to the first input signal. The biasing signal may be applied to the first and second cascode transistors that may be cascoded to the first and second input transistors, respectively.
1. Circuitry for processing signals, the circuitry comprising:
a first PMOS transistor with a source terminal coupled to a positive voltage supply;
a drain terminal of the first PMOS transistor coupled to a source terminal of each of a second PMOS transistor and a third PMOS transistor;
a fourth PMOS transistor with a source terminal coupled to the drain terminal of the second PMOS transistor;
a fifth PMOS transistor with a source terminal coupled to the drain terminal of the third PMOS transistor;
a first NMOS transistor with a drain terminal coupled to a drain terminal of the fourth PMOS transistor, to a gate terminal of the first NMOS transistor, to a drain terminal of a second NMOS transistor, and to a gate terminal of a third NMOS transistor;
a fourth NMOS transistor with a drain terminal coupled to a drain terminal of the fifth PMOS transistor, to a gate terminal of the fourth NMOS transistor, and to a drain terminal of the third NMOS transistor, and to a gate terminal of the second NMOS transistor;
a source terminal of each of the first NMOS transistor, the second NMOS transistor, the third NMOS transistor, the fourth NMOS transistor coupled to ground;
an input ramp signal applied to a gate terminal of the second PMOS transistor and to an input terminal of a cascode bias generator;
an input pixel signal applied to a gate terminal of the third PMOS transistor;
the cascode bias generator having an output terminal coupled to a gate terminal of the fourth PMOS transistor and to a gate terminal of the fifth PMOS transistor; and
the cascode bias generator being configured to produce a cascode biasing signal based on the input ramp signal and provide the cascode biasing signal at its output terminal.
2. The circuitry according to claim 1 , wherein:
a biasing signal applied to a gate terminal of the first PMOS transistor.
3. The circuitry according to claim 1 , wherein the cascode biasing signal, offset by a substantially fixed voltage from the first input ramp signal, tracks the first input ramp signal.
4. The circuitry according to claim 1 , wherein a first differential output signal is at the node where the drain terminals of the first and second NMOS transistors are coupled, and a second differential output signal is at the node where the drain terminals of the third and fourth NMOS transistors are coupled.