Patent ID: 8193854

Claim:
A bi-directional trimming reference circuit comprising: an op amp having a first input and a second input, the op amp generating an op-amp output from a voltage difference between the first input and the second input; a generating transistor, having a gate receiving the op-amp output and generating a bandgap reference voltage on a bandgap reference node in response to the op-amp output; a plurality of trimming-up resistor cells connected in series between the bandgap reference node and a first node, the plurality of trimming-up resistor cells having a first variable resistance that is determined by programming; a sensing resistor connected between the first node and a splitting node; a first parallel resistor connected between the splitting node and the first input to the op amp; a first bipolar transistor connected to the first input of the op amp; a second parallel resistor connected between the splitting node and the second input to the op amp; a difference resistor connected between the second input to the op amp and a second node; a second bipolar transistor connected to the second node, and having a base connected to a base of the first bipolar transistor; a plurality of trimming-down resistor cells connected in series between the bandgap reference node and a third node, the plurality of trimming-down resistor cells having a second variable resistance that is determined by programming; and an output resistor connected between the third node and a reference output node.