Digital to Analog Converters. Tyler Smith Brent Nelson Jerry Jackson. 10/14/04. Topics Discussed. What is a DAC? Choosing a DAC Resistor String DAC Weighted Resistor DAC R-2R DAC PWM DAC associated errors Applications Conclusion. What is a DAC.
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There are six main parameters that should be considered when choosing a DAC for a particular project.
To a large extent the output properties of a DAC are determined by the reference voltage.
Multiplier DAC – The reference voltage is constant and is set by the manufacturer.
Non-Multiplier DAC – The reference voltage can be changed during operation.
The resolution is the amount of voltage rise created by increasing the LSB of the input by 1. This voltage value is a function of the number of input bits and the reference voltage value.
- Increasing the number of bits results in a finer resolution
- Most DACs in the 12-18 bit range
The linearity is the relationship between the output voltage and the digital signal input.
Usually specified as the conversion rate or sampling rate. It is the rate at which the input register is cycled through in the DAC.
Ideally a DAC would instantaneously change its output value when the digital input would change. However, in a real DAC it takes time for the DAC to reach the actual expected output value.
There are multiple sources of error in computing the analog output.
An example of a DAC would be the Analog Devices AD 7224 D/A Converter. The AD7224 is a precision 8-bit, voltage-output, digital-to-analog converter with an output amplifier.
DAC Type – R-2R Voltage Out
Input – Dual 8 Bit
Reference voltage – Non-Multiplier
2v – 12.5v
Settling Time - 7μs
Cost - Under $4.00
1. Resistor String
2. N-Bit Binary Weighted Resistor
3. R-2R Ladder
4. PWM DAC
Number of Resistors =
Number of Switches =