WM8196
Production Data
ADC INPUT BLACK LEVEL ADJUST
The output from the PGA should be offset to match the full-scale range of the ADC (3V). For
negative-going input video signals, a black level (zero differential) output from the PGA should be
offset to the top of the ADC range by setting register bits PGAFS[1:0]=10. For positive going input
signal the black level should be offset to the bottom of the ADC range by setting PGAFS[1:0]=11.
Bipolar input video is accommodated by setting PGAFS[1:0]=00 or PGAFS[1:0]=01 (zero differential
input voltage gives mid-range ADC output).
OVERALL SIGNAL FLOW SUMMARY
Figure 14 represents the processing of the video signal through the WM8196.
OUTPUT
INVERT
BLOCK
INPUT
SAMPLING
BLOCK
OFFSET DAC PGA
ADC BLOCK
BLOCK
BLOCK
D2
x (65535/VFS
)
V1
V2
V3
D1
+0
if PGAFS[1:0]=11
X
+65535 if PGAFS[1:0]=10
+32768 if PGAFS[1:0]=0x
OP[7:0]
+
+
VIN
digital
analog
+
-
CDS = 1
CDS = 0
D2 = D1 if INVOP = 0
D2 = 65535-D1 if INVOP = 1
VRESET
PGA gain
A = 208/(283-PGA[7:0])
VVRLC
Offset
DAC
260mV*(DAC[7:0]-127.5)/127.5
VIN is RINP or GINP or BINP
VRESET is VIN sampled during reset clamp
VRLC is voltage applied to VRLC pin
RLCEXT=1
RLCEXT=0
CDS, RLCEXT,RLCV[3:0], DAC[7:0],
PGA[7:0], PGAFS[1:0] and INVOP are set
by programming internal control registers.
CDS=1 for CDS, 0 for non-CDS
RLC
DAC
See parametrics for
DAC voltages.
Figure 14 Overall Signal Flow
The INPUT SAMPLING BLOCK produces an effective input voltage V1. For CDS, this is the
difference between the input video level VIN and the input reset level VRESET. For non-CDS this is the
difference between the input video level VIN and the voltage on the VRLC/VBIAS pin, VVRLC
optionally set via the RLC DAC.
,
The OFFSET DAC BLOCK then adds the amount of fine offset adjustment required to move the
black level of the input signal towards 0V, producing V2.
The PGA BLOCK then amplifies the white level of the input signal to maximise the ADC range,
outputting voltage V3.
The ADC BLOCK then converts the analogue signal, V3, to a 16-bit unsigned digital output, D1.
The digital output is then inverted, if required, through the OUTPUT INVERT BLOCK to produce D2.
CALCULATING OUTPUT FOR ANY GIVEN INPUT
The following equations describe the processing of the video and reset level signals through
the WM8196. The values if V1 V2 and V3 are often calculated in reverse order during device
setup. The PGA value is written first to set the input Voltage range, the Offset DAC is then
adjusted to compensate for any Black/Reset level offsets and finally the RLC DAC value is
set to position the reset level correctly during operation.
Note: Refer to WAN0123 for detailed information on device calibration procedures.
INPUT SAMPLING BLOCK: INPUT SAMPLING AND REFERENCING
If CDS = 1, (i.e. CDS operation) the previously sampled reset level, VRESET, is subtracted from the
input video.
V1
=
VIN - VRESET ................................................................... Eqn. 1
If CDS = 0, (non-CDS operation) the simultaneously sampled voltage on pin VRLC is subtracted
instead.
V1
=
VIN - VVRLC .................................................................... Eqn. 2
If RLCEXT = 1, VVRLC is an externally applied voltage on pin VRLC/VBIAS.
PD Rev 4.3 March 2007
16
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WOLFSON [ WOLFSON MICROELECTRONICS PLC ]
