There are a few ways we typically classify DACs. These classifications are based upon the characteristics and function of the DAC.
A DAC may have either a voltage output or a current output, depending upon its design. The voltage output DAC is preferred for most applications, but a current output DAC on the same fabrication process will have a faster settling time.
- All DACs are multipliers in that their output is the product of the input word and a reference voltage or current. Most DACs are designed to function well over a narrow range of d.c. reference voltages or currents. But a DAC that is called a multiplying DAC is special in that it is designed to function well with an a.c. signal at the reference input, allowing the DAC to be used as a digital attenuator.
- One type of multiplying DAC is a single quadrant one where the reference and output each can only be positive for proper functioning.
- Another type of multiplying DAC is a two quadrant one where the reference must be positive but the output can take on positive or negative values, or where the reference can be positive or negative but the output can only be positive. Most commonly, a two quadrant DAC is limited to a positive only reference.
- The four quadrant multiplying DAC may have both reference and output values that can be either positive or negative.
The multiplying DAC is also called an MDAC.
- The Trim DAC is used to trim the offset or gain of other circuits and is actually more of an application than a particular DAC design, except that these devices generally use a fairly low reference value as its output range does not need to be very great.
It's True! TRUE: A negative reference and/or output can be single-ended, in which case a negative supply is needed, or they can be differential, where a negative value is defined as the minus reference input or analog output having a higher current or voltage than does the positive reference input or analog output.
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