Low Noise Quantized Feedback Configuration

An apparatus, comprising:

• a voltage to current converter comprising:
• first and second transistors, each transistor having a gate, a source and a drain;
• an input signal source connected between the gates of the first and second transistors;
• a resistor connected between the sources of the first and second transistors;
• a first current source connected to the source of the first transistor and to a power supply;
• a second current source connected to the source of the second transistor and to a power supply;
• wherein there is a difference between current from the drain of the first transistor and current from the drain of the second transistor, the difference between the currents representing the input signal;
• a capacitor connected between the drain of the first transistor and the drain of the second transistor;
• a third transistor having a gate, a source and a drain, the source and gate connected to the drain of the first transistor;
• a fourth transistor having a gate, a source and a drain, the source connected to the drain of the first transistor;
• a fifth transistor having a gate, a source and a drain, the source and gate connected to the drain of the second transistor and to the gate of the fourth transistor;
• a sixth transistor having a gate, a source and a drain, the source connected to the drain of the first transistor and to the gate of the third transistor;
• a switch connected to the drains of the third, fourth, fifth and sixth transistors and having two positions, a first position connecting the drains of the third and fourth transistors to a ground and leaving the drains of the fifth and sixth transistors unconnected to the ground, and a second position connecting the drains of the fifth and sixth transistors to the ground and leaving the drains of the third and fourth transistor unconnected to the ground;
• and
• a control circuit that measures voltage across the capacitor and causes the switch to change between the two positions to maintain an average value of charge on the capacitor at zero.