Data Sheet
Theory of Operation
The CDK1301 is a three-step subranger. It consists of
two THAs in series at the input, followed by three ADC
blocks. The first block is a three-bit folder with over/under
range detection. The second block consists of two single-
bit folding interpolator stages. There are pipelining THAs
between each ADC block.
The analog decode functions are the input buffer, input
THAs, three-bit folder, folding interpolators, and pipelining
THAs. The input buffer enables the part to withstand rail-
to-rail input signals without latchup or excessive currents
and also performs single-ended to differential conversion.
All of the THAs have the same basic architecture. Each
has a differential pair buffer followed by switched emitter
followers driving the hold capacitors. The input THA also
has hold mode feedthrough cancellation devices.
The three MSBs of the ADC are generated in the first
threebit folder block, the output of which drives a dif-
ferential reference ladder which also sets the full-scale
input range. Differential pairs at the ladder taps gener-
ate midscale, quarter and three-quarter scale, overrange,
and underrange. Every other differential pair collector is
cross-coupled to generate the eighth scale zero crossings.
The middle ADC block generates two bits from the folded
signals of the previous stages after pipeline THAs. Its out-
puts drive more pipeline THAs to push the decoding of the
three LSBs to the next half clock cycle. The three LSBs are
generated in interpolators that are latched one full clock
cycle after the MSBs.
The digital decode consists of comparators, exclusive of
cells for gray to binary decoding, and/or cells used for
mostly over/under range logic. There is a total of 2.5
clock cycles latency before the output bank selection. In
order to reduce sparkle codes and maintain sample rate,
no more than three bits at a time are decoded in any half
clock cycle.
The output data mode is controlled by the state of the
demux mode inputs. There are three output modes:
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CDK1301
8-bit, 250 MSPS A/D Converter with Demuxed Outputs
All data on bank A with clock rate limited to one-half
maximum
Interleaved mode with data alternately on banks A and
B on alternate clock cycles
Parallel mode with bank A delayed one cycle to be
synchronous with bank B every other clock cycle
n
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If necessary, the input clock is divided by two. The
divided clock selects the correct output bank. The user
can synchronize with the divided clock to select the
desired output bank via the differential RESET input.
The output logic family is CMOS with output OVDD supply
adjustable from 2.7V to 5.25V. There are also differential
clock output pins that can be used to latch the output data
in single bank mode or to indicate the current output bank
in demux mode.
Finally, a power-down mode is available, which causes the
outputs to become tri-state, and overall power is reduced
to about 24mW. There is a 2V reference to supply com-
mon mode for single-ended inputs that is not shut down
in powerdown mode.
REV 1A
Figure 1. Single Mode Timing Diagram
©2008 CADEKA Microcircuits LLC
www.cadeka.com
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CADEKA [ CADEKA MICROCIRCUITS LLC. ]
