ADC_DCLKOUT
ADCDATA <11:0>
A
B
A
B
A
B
SLOS711B – NOVEMBER 2011 – REVISED MARCH 2012
Clocking:
By default, the device expects a differential clock on CLKINP and CLKINN. This differential clock is used
to drive both the ADC and DAC.
In case the clock source is single ended, then short CLKINN to a voltage of 0.95V and apply the single
ended clock source on CLKINP – alternatively, CLKINP can be driven with a voltage of 0.95V and the
single ended clock source can be applied on CLKINN.
A third alternative is to use the single ended clock buffer inside the device. This mode saves about 9 mW
of power since the differential clock buffer is shut down. By setting register (address 20A, Data 20), the
single ended clock buffer can be enabled. In that case, Pin 8 provides the single ended clock for the DAC
whereas Pin 9 provides the single ended clock for the ADC – if a single clock source is to be used for
both, then tie pins 8 and 9 to this clock source.
Biasing the ADC inputs:
The common mode of the ADC input pins should set to VCM, which is nominally 0.95V (measured after
programming the initialization registers). Deviating from this input common mode can cause degraded
performance. The full scale input swing on the inputs is 2 Volt differential peak-to-peak. When biased
optimally at 0.95V, the device gives a full scale output code when the positive input swings between
roughly 0.45V and 1.45V (and correspondingly the negative input swings between 1.45V and 0.45V). It is
recommended to operate the ADC at an input that is at least 1 dB below full scale.
ADC output format:
The ADC gives out a 12-bit output in 2s complement format. For the most negative input, the ADC gives
out a code of 100000000000. For the most positive input, the output code is 011111111111.
RX data output capture (CMOS mode) :
The RX output data format is DDR (Dual data rate) CMOS. The output of the ADC channel A can be
captured using the rising edge of ADC_DCLKOUT. The output of ADC channel B can be captured using
the falling edge of ADC_DCLKOUT. The clock rate of ADC_DCLKOUT matches with the input clock rate
(on CLKINP, CLKINN).
Figure 11-1. RX CMOS Output Interface
A variety of test patterns can be output by the device in order to debug issues with the capture. To enable
the test patterns, program register address 042, Data 08. Once this register is programmed, we can
change the output pattern as follows :
TO REPLACE NORMAL DATA WITH THE FOLLOWING
.. ON CHANNEL A WRITE
.. ON CHANNEL B WRITE
All bits 0
Address 031, Data 01
Address 037, Data 01
All bits 1
Address 031, Data 02
Address 037, Data 02
All bits toggle between 0 and 1
Address 031, Data 03
Address 037, Data 03
Linearly ramping code that ramps through min to max code
Address 031, Data 04
Address 037, Data 04
12-bit Custom code
Address 031, Data 05
Address 037, Data 05
The 12 bits for the custom code (C<11 :0>) can be set (common for Channel A and B) using the following
bits:
C<11> = Bit D5 of regster address 03F
C<10> = Bit D4 of regster address 03F
C<9> = Bit D3 of regster address 03F
Copyright 2011–2012, Texas Instruments Incorporated
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