WM8253
Production Data
CALCULATING OUTPUT FOR ANY GIVEN INPUT
The following equations describe the processing of the video and reset level signals through
the WM8253.
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 VRLCEXT = 1, VVRLC is an externally applied voltage on pin VRLC/VBIAS.
If VRLCEXT = 0, VVRLC is the output from the internal RLC DAC.
VVRLC
=
(VRLCSTEP RLCV[3:0]) + VRLCBOT ..................................... Eqn. 3
VRLCSTEP is the step size of the RLC DAC and VRLCBOT is the minimum output of the RLC DAC.
OFFSET DAC BLOCK: OFFSET (BLACK-LEVEL) ADJUST
The resultant signal V1 is added to the Offset DAC output.
V2
=
V1 + {260mV (DAC[7:0]-127.5) } / 127.5 ...................... Eqn. 4
PGA NODE: GAIN ADJUST
The signal is then multiplied by the PGA gain,
V3
=
V2 [0.78+(PGA[7:0]*7.57)/255] ..................................... Eqn. 5
ADC BLOCK: ANALOGUE-DIGITAL CONVERSION
The analogue signal is then converted to a 16-bit unsigned number, with input range configured by
PGAFS[1:0].
D1[15:0] = INT{ (V3 /VFS) 65535} + 32767 PGAFS[1:0] = 00 or 01 ...... Eqn. 6
D1[15:0] = INT{ (V3 /VFS) 65535}
PGAFS[1:0] = 11 ................ Eqn. 7
D1[15:0] = INT{ (V3 /VFS) 65535} + 65535 PGAFS[1:0] = 10 ................ Eqn. 8
where the ADC full-scale range, VFS = 2.0V
if D1[15:0] < 0
D1[15:0] = 0
if D1[15:0] > 65535 D1[15:0] = 65535
OUTPUT INVERT BLOCK: POLARITY ADJUST
The polarity of the digital output may be inverted by control bit INVOP.
D2[15:0] = D1[15:0]
(INVOP = 0) ....................... Eqn. 9
(INVOP = 1) ....................... Eqn. 10
D2[15:0] = 65535 – D1[15:0]
PD, Rev 4.1, August 2011
14
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WOLFSON [ WOLFSON MICROELECTRONICS PLC ]
