Technical Articles and Editorials

AVR - Audio Video Receiver - Build Quality: Part I

ARTICLE INDEX

Enhanced Distortion Performance with Current Mode DACs

DACs come in two types. DACs with a current output (current-mode DAC) require high-quality external opamps to convert the DAC's current output to a voltage. The current-to-voltage converter stage is often abbreviated as I/V.

A current-mode DAC allows the output pins of the DAC to stay at analog ground instead of moving with the music signal. This improves the distortion performance of the DAC. The I/V converter, as the name implies, produces a voltage output in proportion to the current flowing from the DAC. For reasons that will be outlined below, producing a very high performance opamp is difficult when the chip must perform other function. Since the I/V converter is a stand-alone opamp, it does the job more accurately (lower noise and distortion).

All current mode DACs have balanced outputs thus two I/V converters are required

Voltage output DACs put the opamps inside the chip, which prevents inherent THD from exceeding -100 dB worst case. The advantage of a DAC with a voltage output is that the two external opamps and the associated passive parts need not be placed on the PC board, reducing cost. All lower performance DACs have transitioned to voltage outputs to save the cost of the extra opamps.