US 8,618,971 B1Granted

Signal level shift circuit and method for dual resistor ladder digital-to-analog converters

AssigneeTexas Instruments Incorporated

InventorQunying Li

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Abstract

A dual resistor ladder DAC includes a coarse ladder including a plurality of coarse ladder resistors and a fine ladder including a plurality of MOS transistors coupled between first and second conductors. A first group of parallel-connected bit-shifting transistors is coupled between the first and third conductors. A second group of parallel-connected MOS bit-shifting transistors is coupled between the third and top conductors. A third group of parallel-connected bit-shifting transistors is coupled between bottom and fourth conductors. A fourth group of parallel-connected bit-shifting transistors is coupled between the second and fourth conductors. Parallel-connected bit-shifting transistors are turned either on or off in response to a plurality of bit-switching bits of a binary number to be converted. One of the bottom, first, second, third, and top conductors is coupled to a DAC output conductor in response to the plurality of bit-switching bits.

Claims20

Dependent claims

A digital-to-analog converter (DAC) comprising:

(a) a coarse ladder including a first linear sequence of series-connected coarse ladder resistive devices, and a plurality of coarse ladder nodes coupled between various series-connected coarse ladder resistive devices, respectively;
(b) a fine ladder including
a second linear sequence of series-connected MOS (metal oxide semiconductor) fine ladder transistors coupled between a first conductor and a second conductor and biased to operate in their deep triode regions,
a first group of parallel-connected MOS programmable bit-shifting transistors each coupled between the first conductor and a third conductor, and a second group of parallel-connected MOS programmable bit-shifting transistors each coupled between the third conductor and a top conductor, and
a third group of parallel-connected MOS programmable bit-shifting transistors each coupled between a bottom conductor and a fourth conductor, and a fourth group of parallel-connected MOS programmable bit-shifting transistors each coupled between the second conductor and the fourth conductor, the programmable bit-shifting transistors being programmable to be either turned either on or off, respectively, in response to a plurality of bit-switching bits of a binary number to be converted;
and
(c) bit-shifting resistor switching circuitry including a plurality of bit-shifting switching transistors configured to couple a predetermined one of the bottom conductor, the fourth conductor, the third conductor and the top conductor to a DAC output conductor in response to the plurality of bit-switching bits to provide increased resolution of the DAC.

4 more elements

A method for increasing the resolution of a dual resistor ladder digital-to-analog converter (DAC) including a coarse ladder including a first linear sequence of series-connected coarse ladder resistive devices and a plurality of coarse ladder nodes connected between various series-connected coarse ladder resistive devices, respectively, and also including a fine ladder including a second linear sequence of series-connected MOS (metal oxide semiconductor) fine ladder transistors coupled between a first conductor and a second conductor, the method comprising:

(a) coupling a first group of parallel-connected MOS programmable bit-shifting transistors between the first conductor and a third conductor, and coupling a second group of parallel-connected MOS programmable bit-shifting transistors between the third conductor and a top conductor;
(b) coupling each of a third group of parallel-connected MOS programmable bit-shifting transistors between a bottom conductor and a fourth conductor, and coupling a fourth group of parallel-connected MOS programmable bit-shifting transistors between the second conductor and the fourth conductor;
(c) turning various parallel-connected MOS programmable bit-shifting transistors either on or off in response to a plurality of bit-switching bits of a binary number to be converted, to provide a plurality of bits of increased resolution;
and
(d) coupling one of the bottom conductor, first conductor, second conductor, third conductor, and top conductor to a DAC output conductor in response to the plurality of bit-switching bits, to produce an analog output signal having accuracy representative of the increased resolution.

2 more elements

Dependencies are inferred from the claim text.