ICL7134

The ICL7134 combines a four-quadrant multiplying DAC using thin film resistor and CMOS circuitry with an on-chip PROM-controlled correction circuit to achieve true 14-bit linearity without laser trimming.

Microprocessor bus interfacing of the ICL7134 is eased using standard memory WRITE cycle timing and control signal use. Two input buffer registers are separately loaded with the 8 least significant bits (LS register) and the 6 most significant bits (MS register). Their contents are then transferred to the 14-bit DAC register, which controls the current switches. The DAC register can also be loaded directly from the data inputs, in which case the MS and LS registers are transparent.

The ICL7134 is available in two versions. The ICL7134U is programmed for unipolar operation while the ICL7134B is programmed for bipolar applications. The VREF input to the most significant bit of the DAC is separated from the
reference input to the remainder of the ladder. For unipolar use, the two reference inputs are tied together, while for bipolar operation, the polarity of the MSB reference is reversed, giving the DAC a true 2's complement input transfer function. Two resistors which facilitate the reference inversion are included on the chip, so only an external op-amp is needed. The PROM of the ICL7134 is coded to correct for errors in these resistors as well as the inversion of the MSB.