WM8143-12 Wolfson Microelectronics Ltd., WM8143-12 Datasheet - Page 11

• Manufacturer Part Number: WM8143-12
• Description: WM8143 : 10 or 12-BIT, 4MSPS Analogue Front End For CCD Image Sensors
• Manufacturer: Wolfson Microelectronics Ltd.

Production Data
Figure 7 RLC TimingVideo Sampling Options
Video Sampling Options
The WM8143-12 can interface to CCD sensors using
six basic modes of operation (summarised in Table 3).
Mode configurations are controlled by a combination of
control bits and timing applied to MCLK and VMSP
pins. The default operational mode is mode 1: colour
with CDS enabled.
Colour Mode Definition (Mode 1)
Figure 9 summarises the timing relationships. MCLK is
applied at twice the required ADC conversion rate.
Synchronisation of sampling and channel multiplexing
to the incoming video signal is performed by the VSMP
pulse (active high). The three input channels (R,G,B)
are sampled in parallel on the rising edge of MCLK
following a VSMP pulse. The sampled data is
multiplexed into a single data stream at three times the
VSMP rate and passes through the internal pipeline
and emerges on the OP[11:0] bus. Both Correlated
Double Sampling (CDS) and Single Ended modes of
operation are available.
Monochrome Mode Definitions
One input channel is continuously sampled on the
rising edge of MCLK following a VSMP pulse. The user
can specify which input channel (R,G,B) is to be
sampled by writing to the WM8143-12 internal control
registers. There are four separate monochrome modes
with different maximum sample rates and CDS
availability.
Monochrome Mode (Mode 2)
Figure 10 summarises the timing relationships. The
timing in this mode is identical to mode 1 except that
one input channel is sampled three times (due to the
multiplexer being held in one position) and passes
through the device as three separate samples. The last
two samples can be ignored at the output OP[11:0].
Input video
MCLK
VSMP
RLC
r,g,b
1
X
X
RLC on this pixel
r,g,b
0
X
X
No RLC on this pixel
Wolfson Microelectronics
r,g,b
0
X
11
Fast Monochrome Mode (Mode 3)
Figure 11 summarises the timing relationships. This
mode allows the maximum sample rate to be increased
to 2.67 MSPS. This is achieved by altering the
MCLK:VSMP ratio to 3:1. In this mode, the timing of
RS and CL must be fixed (refer to Table 3). The
sampled video data will pass through the internal
pipeline and emerge on the OP[11:0] bus.
Max. Speed Monochrome Mode (Mode 4)
Figure 12 summarises the timing relationships. This
mode allows the maximum sample rate to be increased
to 4 MSPS. This is achieved by altering the
MCLK:VSMP ratio to 2:1. The latency through the
device is identical to modes 1 and 2. CDS is not
available in this mode.
Slow Colour Mode (Mode 5)
Figure 13 summarises the timing relationships. This
mode is identical to Mode 1 except that the MCLK to
VSMP ratio is 8 : 1 and the maximum sample rate is 1
MSPS.
sample position and the reset sample position, Setup
Register 3 CDSREF1-0 control bits b[5:4] should be set
to 10. The first three of the four output words are valid.
Slow Monochrome Mode (Mode 6)
Figure 14 summarises the timing relationships. This
mode is identical to mode 2 except that the MCLK to
VSMP ratio is 8 : 1 and the maximum sample rate is 1
MSPS.
sample position and the reset sample position, Setup
Register 3 CDSREF 1-0 control bits b[5:4] should be
set to 10. The first of the four output words is the only
valid output.
Input Impedance
The input impedance of the WM8143-12 is dependent
upon the sampling frequency of the input signal and the
gain that the PGA is set to. This is due to the effective
capacitance of the ‘sample and hold’ circuits (Figure 8).
Figure 8 Input Impedance S/H Circuit
RINP/VMID
To obtain a ratio of 4:4 between the video
To obtain a ratio of 4:4 between the video
VS/RS
S/H
C
VMID
WM8143-12
PD. Rev 4 Nov. 99
PGA