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Maxim > Design Support > Technical Documents > Application Notes > A/D and D/A Conversion/Sampling Circuits > APP 3853
Maxim > Design Support > Technical Documents > Application Notes > Basestations/Wireless Infrastructure > APP 3853
Maxim > Design Support > Technical Documents > Application Notes > Digital Potentiometers > APP 3853
Keywords: pre equalization, post equalization, frequency response, sinx/x, sinc function, interpolation,
Nyquist, image frequency, reconstruction filter, FIR, roll-off
APPLICATION NOTE 3853
Equalizing Techniques Flatten DAC Frequency
Response
Aug 20, 2012
Abstract: Digital-to-analog converters (DACs) convert digital data to analog voltage or current in
applications such as instrumentation and wireless communications. A DAC's output frequency generally
ranges from DC to less than f
S
/2, where f
S
is the input-updating frequency. The output frequency response
for most DACs, however, rolls off according to the sin(x)/x (sinc) frequency-response envelope.
In the generic example of Figure 1, a digital baseband signal is
sampled by the DAC. The DAC's frequency response is not flat and
attenuates the analog output at higher frequencies. At 80% of
f
NYQUIST
, for instance (f
NYQUIST
= f
S
/2), the frequency response is
attenuated by 2.42dB. That loss is unacceptable for some broadband
applications requiring a flat frequency response. Fortunately, however,
several techniques are available for coping with the non-flat
frequency response of a DAC. These include increasing the DAC's
update rate, as well as using interpolation techniques, pre-
equalization filtering, and post-equalization filtering—all of which
reduce or eliminate the effects of the sinc rolloff.
Figure 1. The non-flat frequency response of a DAC attenuates the output signal, especially at high
frequencies.
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