AS1419
AS1419A
CONVERSION DETAILS
The AS1419 uses a successive approximation algorithm
and an internal sample-and-hold circuit to convert an analog
signal to a 14-bit parallel output. The ADC is complete with
a precision reference and an internal clock. The control logic
provides easy interface to microprocessors and DSPs (please
refer to Digital Interface section for the data format).
Conversion start is controlled by the CS\ and CONVST\
inputs. At the start of the conversion, the successive
ap-
proximation register (SAR) is reset. Once a conversion cycle
has begun, it cannot be restarted.
ADC
The AS1419 has excellent high speed sampling capabil-
ity. FFT (Fast Fourier Transform) test techniques are used to
test the ADC’s frequency response, distortion and noise at the
rated throughput. By applying a low distortion sine wave and
analyzing the digital output using an FFT algorithm, the ADC’s
spectral content can be examined for frequencies outside the
fundamental. Figure 2 shows a typical AS1419 FFT plot.
FIGURE 1: Simplified Block Diagram
During the conversion, the internal differential 14-bit
capacitive DAC output is sequenced by the SAR from the
most significant bit (MSB) to the least significant bit (LSB).
Referring to Figure 1, the +A
IN
and –A
IN
inputs are connected
to the sample-and-hold capacitors (C
SAMPLE
) during the ac-
quire phase and the comparator offset is nulled by the zeroing
switches. In this acquire phase, a minimum delay of 200ns
will provide enough time for the sample-and-hold capacitors
to acquire the analog signal. During the convert phase, the
comparator zeroing switches open, putting the comparator into
compare mode. The input switches the C
SAMPLE
capacitors to
ground, transferring the differential analog input charge onto the
summing junction. This input charge is successively compared
with the binary weighted charges supplied by the differential
capacitive DAC. Bit decisions are made by the high speed
comparator. At the end of a conversion, the differential DAC
output balances the +A
IN
and –A
IN
input charges. The SAR
contents (a 14-bit data word) which represents the difference
of +AIN and –AIN are loaded into the 14-bit output latches.
DYNAMIC PERFORMANCE
AS1419 & AS1419A
Rev. 1.7 06/10
Micross Components reserves the right to change products or specifications without notice.
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