US 6,583,744 B2 · Correction circuit for beta mismatch between thermometer encoded and R-2R ladder segments of a current steering DAC

Abstract

A current correction circuit 500 eliminates beta mismatches between a thermometer encoded segment 102 and a R-2R ladder segment 106 of a current steering digital-to-analog converter 100. The circuit 500 consists of three replica MSB unit current sources, I1, I2 and I3. The replica current I1 acts as a replica to a cascode device 206 of the MSB unit 200 of the current steering DAC 100. The replica current I2 replicates an effective base current equal to the total base current in the R-2R ladder circuit portion 300 of the current steering DAC 100. The replica current I3 replicates the total base current of the L output switches 310 in the LSB segment 106 of the current steering DAC 100. A high impedance summing node 506 produces a correction current ICOR=I1−(I2+I3). This current is equal to the current difference between an MSB unit 200 and the LSB segment 106. This correction current is then subtracted from the MSB unit current source 200 that supplies current into the R-2R ladder 300 such that the current supplied to the R-2R ladder 300 will be equal to the MSB replica current source minus the correction current.

Claims21

Dependent claims

A current correction circuit comprising:

a first current generating circuit operational to produce a first replica current equal to a most significant bit (MSB) unit cascode device base current associated with a MSB segment of a digital-to-analog converter (DAC);
a second current generating circuit operational to produce a second replica current equal to a total device base current of an R-2R ladder circuit portion of a least significant bit (LSB) segment of a DAC;
a third current generating circuit operational to produce a third replica current equal to a total device base current of an output switch portion of the LSB segment of a DAC;
a first high impedance summing circuit operational to sum the second and third replica currents and generate a negative current equal to a total combined device base current associated with the LSB segment of the DAC;
and
a second high impedance summing circuit operational to sum the first replica current with the negative current to generate a correction current therefrom such that the correction current is equal to a current difference between an MSB unit and the LSB segment.

3 more elements

A current correction circuit comprising:

a first current generating means for generating a first replica current equal to a most significant bit (MSB) unit cascode transistor base current associated with a thermometer encoded segment of a current steering digital-to-analog converter (DAC);
a second current generating means for generating a second replica current equal to a total transistor base current of an R-2R ladder circuit portion of a binary encoded segment of a current steering DAC;
a third current generating means for generating a third replica current equal to a total transistor base current of an output switch portion of the binary encoded segment of a current steering DAC;
a first summing means for summing the second and third replica currents and generating a negative current therefrom;
and
a second summing means for summing the first replica current with the negative current to generate a correction current therefrom such that the correction current is equal to a difference between a DAC MSB unit current and a DAC LSB segment total effective transistor base current.

3 more elements

A DAC current correction circuit comprising:

a first current generating circuit operational to provide a replicated MSB unit source current into a R-2R ladder circuit portion of a LSB segment of a current steering DAC;
and
a second current generating circuit operational to provide a correction current such that base current mismatches between an MSB unit and the LSB segment are substantially eliminated when the correction current is subtracted from the replicated MSB unit source current.

Dependencies are inferred from the claim text.

Correction circuit for beta mismatch between thermometer encoded and R-2R ladder segments of a current steering DAC

Life of this patent

Correction circuit for beta mismatch between thermometer encoded and R-2R ladder segments of a current steering DAC

Life of this patent

Abstract

Claims21