|AD9020SZ/883||10-Bit 60 MSPS A/D Converter|
|AD9020SZ/883 Datasheet PDF : 12 Pages |
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 stewing 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 both 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 vary-
ing levels are then digitized by applying encode commands at
the correct times, as shown below.
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 AD9020.
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 insure 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 AD9020 to
achieve full accuracy when a step function is applied. Overvolt-
age Recovery Time is the time required for the AD9020 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 AD9020 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.
Imaging Application Using AD9020
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