Apparatuses and methods for providing offset compensation for operational amplifier

An imaging device comprising:

• a first amplifier comprising:
• a non-inverting output;
• an inverting output;
• a first load input;
• and
• a second load input;
• a first feedback loop connected to the first amplifier, the first feedback loop comprising:
• a first switch located between the inverting output of the first amplifier and the first load input;
• and
• a first offset capacitor, a first plate of the first offset capacitor being coupled to the first switch between the first switch and the first load input;
• and a second plate of the first offset capacitor being coupled to ground;
• and
• a second feedback loop connected to the first amplifier, the second feedback loop comprising:
• a second switch located between the inverting output of the first amplifier and the second load input;
• and
• a second offset capacitor, a first plate of the second offset capacitor being coupled to the second switch between the second switch and the second load input, and a second plate of the second offset capacitor being coupled to ground.

A camera system comprising:

• a differential telescopic operational amplifier comprising:
• a first output;
• a second output;
• a first load input;
• and
• a second load input;
• a first feedback loop connected to the differential telescopic operational amplifier, the first feedback loop comprising:
• a first switch located between the first output of the differential telescopic operational amplifier and the first load input;
• and
• a first offset capacitor, a first plate of the offset capacitor being coupled to the first switch between the first switch and the first load input, and a second plate of the first offset capacitor being coupled to ground;
• a second feedback loop connected to the differential telescopic operational amplifier, the second feedback loop comprising:
• a second switch located between the second output of the differential telescopic operational amplifier and the second load input;
• and
• a second offset capacitor, a first plate of the second offset capacitor being coupled to the second switch between the second switch and the second load input, and a second plate of the second offset capacitor being coupled to ground;
• and
• an input switching circuit for connecting an input common mode voltage to the first and second inputs of the differential telescopic operational amplifier.

A differential telescopic operational amplifier comprising:

• a first load transistor for receiving a first load at a gate;
• and
• a second load transistor for receiving a second load at a gate;
• a third transistor having a source/drain region coupled to a source/drain region of the first load transistor and a second source/drain region coupled to a first amplifier output;
• and
• a fourth transistor having a first source/drain region coupled to a source/drain region of the second load transistor and a second source/drain region coupled to a second amplifier output, the third and fourth transistors each having gates coupled together and connected to a first bias line;
• a fifth transistor having a first source/drain region coupled to the second source/drain region of the third transistor and the first amplifier output;
• and
• a sixth transistor having a first source/drain region coupled to the second source/drain region of the fourth transistor and the second amplifier output, the fifth and sixth transistors each having gates coupled together and connected to a second bias line;
• a seventh transistor having a first source/drain coupled to a second source/having region of the fifth transistor, a gate coupled to a first signal input, and a second source/drain region coupled to a third bias line;
• and
• an eighth transistor having a first source/drain region coupled to a second source/drain region of the sixth transistor, a gate coupled to a second signal input, and a second source/drain region coupled to the third bias line.

A method of providing offset compensation for a differential telescopic operational amplifier, the method comprising:

• connecting first and second differential outputs of a differential telescopic operational amplifier to respective first and second gates of respective first and second load transistors;
• connecting first and second inputs of the operational amplifier to an input common mode voltage;
• forming respective offset voltage feedback loops between the first and second gates of the first and second load transistors and the first and second differential outputs;
• and
• sampling first and second differential offset voltages at the first and second differential outputs of the operational amplifier in respective first and second offset capacitors, a first plate of the first and second offset capacitors being respectively connected to the gates of the first and second load transistors, and a second plate of the first and second offset capacitors being respectively connected to ground.