|AD9060||10-Bit 75 MSPS A/D Converter|
|AD9060 Datasheet PDF : 12 Pages |
Two-Tone Intermodulation Distortion (IMD) is a frequently cited
specification in receiver design. In narrow-band receivers, third-
order IMD products result in spurious signals in the pass band
of the receiver. Like mixers and amplifiers, the ADC is charac-
terized with two, equal amplitude, pure input frequencies. The
IMD equals the ratio of the power of either of the two input sig-
nals to the power of the strongest third order IMD signal. Un-
like mixers and amplifiers, the IMD does not always behave as it
does in linear devices (reduced input levels do not result in pre-
dictable reductions in IMD).
Performance graphs provide typical harmonic and SNR data for
the AD9060 for increasing analog input frequencies. In choosing
an A/D converter, always look at the dynamic range for the ana-
log input frequency of interest. The AD9060 specifications pro-
vide guaranteed minimum limits at three analog test frequencies.
Aperture Delay is the delay between the rising edge of the EN-
CODE command and the instant at which the analog input is
sampled. Many systems require simultaneous sampling of more
than one analog input signal with multiple ADCs. In these situ-
ations timing is critical, and the absolute value of the aperture
delay is not as critical as the matching between devices.
Aperture Uncertainty, or jitter, is the sample-to-sample variation
in aperture delay. This is especially important when sampling
high slew rate signals in wide bandwidth systems. Aperture un-
certainty is one of the factors that degrades dynamic perfor-
mance as the analog input frequency is increased.
Oscilloscopes provide amplitude information about an observed
waveform with respect to time. Digitizing oscilloscopes must ac-
curately sample this signal without distorting the information to
One figure of merit for the ADC in these applications is Effective
Number of Bits (ENOBs). ENOB is calculated with a sine wave
curve fit and equals:
ENOB = N – LOG2 [Error (measured)/Error (ideal)]
N is the resolution (number of bits) of the ADC. The measured
error is the actual rms error calculated from the converter out-
puts with a pure sine wave input.
The Analog Bandwidth of the converter is the analog input fre-
quency at which the spectral power of the fundamental signal is
reduced 3 dB from its low frequency value. The analog band-
width is a good indicator of a converter’s slewing capabilities.
The Maximum Conversion Rate is defined as the encode rate at
which the SNR for the lowest analog signal test frequency tested
drops by no more than 3 dB below the guaranteed limit.
Visible and infrared imaging systems each require similar char-
acteristics from ADCs. The signal input (from a CCD camera
or multiplexer) is a time division multiplexed signal consisting
of a series of pulses whose amplitude varies in direct proportion
to the intensity of the radiation detected at the sensor. These
varying levels are then digitized by applying encode commands
at the correct times, as shown below.
Imaging Application Using AD9060
The actual resolution of the converter is limited by the thermal
and quantization noise of the ADC. The low frequency test for
SNR or ENOB is a good measure of the noise of the AD9060.
At this frequency, the static errors in the ADC determine the
useful dynamic range of the ADC.
Although the signal being sampled does not have a significant
slew rate, this does not imply dynamic performance is not im-
portant. The Transient Response and Overvoltage Recovery Time
specifications ensure that the ADC can track full-scale changes
in the analog input sufficiently fast to capture a valid sample.
Transient Response is the time required for the AD9060 to
achieve full accuracy when a step function is applied. Overvolt-
age Recovery Time is the time required for the AD9060 to re-
cover to full accuracy after an analog input signal 150% of full
scale is reduced to the full-scale range of the converter.
Digital Signal Processing (DSP) is now common in television
production. Modern studios rely on digitized video to create
state-of-the-art special effects. Video instrumentation also re-
quires high resolution ADCs for studio quality measurement
and frame storage.
The AD9060 provides sufficient resolution for these demanding
applications. Conversion speed, dynamic performance and ana-
log bandwidth are suitable for digitizing both composite and
RGB video sources.
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