A monolithic 12-bit multiplying DAC for NTSC and HDTV applications

A voltage output digital-to-analog (DAC) that achieves precise dynamic performance with clock rates greater than 70 MHz is described. It was fabricated using an oxide-isolated bipolar process with an F _t of 8 GHz. The minimum finished transistor emitter size is 1.6 μm by 3.9 μm. Additional features include vanadium Schottky diodes, laser-trimmed thin-film NiCr resistors, and two-level gold metallization on a 4-μm metal pitch. The die size is 140 mil×160 mil. The DAC operates from a -5.2-V supply and incorporates an analog multiplying function for output modulation at video speeds. The IC is capable of clock frequencies greater than 250 MHz. The circuit architecture, control amplifier, and voltage generator are discussed. Performance results are reported, showing that the DAC can be used for a wide range of applications in addition to broadcast TV. Low glitching, low noise, and high DC accuracy make it useful for arbitrary waveform generation and direct digital synthesis at data rates up to 250 MHz