Image sensor amplifiers with reduced inter-circulation currents
An image sensor may include an array of image sensor pixels. The array of image sensor pixels may be controlled by row driver circuitry. The row driver circuitry may include row drivers that receive power supply signals from transconductance amplifier circuitry. The transconductance amplifier circuitry may include multiple amplifiers with output ports shorted to one another. Each amplifier may include input transistors, cross-coupled transistors with a low threshold voltage, and additional transistors coupled in series with the cross-coupled transistors and having a moderate or high threshold voltage.
1. An image sensor, comprising:
an array of image sensor pixels;
a plurality of row drivers configured to provide row control signals to the array of image sensor pixels;
a first amplifier having a first output coupled to a first power supply terminal of a first row driver in the plurality of row drivers; and
a second amplifier having a second output coupled to the first output and coupled to a second power supply terminal of a second row driver in the plurality of row drivers, wherein each of the first amplifier and the second amplifier comprises:
a first transistor having a first channel type and having a gate terminal configured as a first amplifier input port;
a second transistor having the first channel type and having a gate terminal configured as a second amplifier input port;
a third transistor having a second channel type different than the first channel type, the third transistor being coupled in series with the first transistor; and
a fourth transistor having the second channel type, the fourth transistor being coupled in series with the second transistor and cross-coupled with the third transistor.
2. The image sensor of claim 1 , wherein each of the first amplifier and the second amplifier further comprises:
a fifth transistor having the second channel type and a first threshold voltage level, wherein the fifth transistor is coupled in series with the third transistor and wherein the third transistor has a second threshold voltage level less than the first threshold voltage level; and
a sixth transistor having the second channel type and the first threshold voltage level, wherein the sixth transistor is coupled in series with the fourth transistor and wherein the fourth transistor has the second threshold voltage level.
3. The image sensor of claim 2 , wherein:
the fifth transistor has a gate terminal that is coupled to a drain terminal of the third transistor; and
the sixth transistor has a gate terminal that is coupled to a drain terminal of the fourth transistor.
4. The image sensor of claim 1 , wherein each of the first amplifier and the second amplifier further comprises:
a fifth transistor having the second channel type and a first threshold voltage level, wherein the fifth transistor is coupled in series with the third transistor and wherein the third transistor has a second threshold voltage different than the first threshold voltage level; and
a sixth transistor having the second channel type and the first threshold voltage level, wherein the sixth transistor is coupled in series with the fourth transistor and wherein the fourth transistor has the second threshold voltage level.
5. The image sensor of claim 1 , wherein each of the first amplifier and second amplifier comprises:
a tail transistor coupled to a source terminal of the first transistor and to a source terminal of the second transistor.
6. The image sensor of claim 1 , wherein:
the first amplifier input port of the first amplifier is shorted to the first output; and
the first amplifier input port of the second amplifier is shorted to the second output.
7. The image sensor of claim 1 , wherein:
the second amplifier input port of the first amplifier is configured to receive a reference voltage; and
the second amplifier input port of the second amplifier is configured to receive the reference voltage.