WM8141 Wolfson Microelectronics Ltd., WM8141 Datasheet - Page 11

• Manufacturer Part Number: WM8141
• Description: WM8141 : 12-BIT 6MSPS Cis/ccd Analogue Front End/digitiser
• Manufacturer: Wolfson Microelectronics Ltd.

Production Data
DEVICE DESCRIPTION
INTRODUCTION
INPUT SAMPLING
RESET LEVEL CLAMPING (RLC)
WOLFSON MICROELECTRONICS LTD
A block diagram of the device showing the signal path is presented on Page 1.
The WM8141 samples up to three inputs (RINP, GINP and BINP) simultaneously. The device then
processes the sampled video signal with respect to the video reset level or an internally/externally
generated reference level using either one or three processing channels.
Each processing channel consists of an Input Sampling block with optional Reset Level Clamping
(RLC) and Correlated Double Sampling (CDS), an 8-bit programmable offset DAC and an 8-bit
Programmable Gain Amplifier (PGA).
The ADC then converts each resulting analogue signal to a 12-bit digital word. The digital output from
the ADC is presented on a 12-bit wide bi-directional bus, with optional 8+4-bit, 6+6-bit or 4+4+4-bit
multiplexed formats.
On-chip control registers determine the configuration of the device, including the offsets and gains
applied to each channel. These registers are programmable via serial or parallel interfaces.
The WM8141 can sample and process one to three inputs through one or three processing channels
as follows:
Colour Pixel-by-Pixel: The three inputs (RINP, GINP and BINP) are simultaneously sampled for
each pixel and a separate channel processes each input. The signals are then multiplexed into the
ADC, which converts all three inputs within the pixel period.
Monochrome: A single chosen input (RINP, GINP, or BINP) is sampled, processed by the
corresponding channel, and converted by the ADC. The choice of input and channel can be changed
via the control interface, e.g. on a line-by-line basis if required.
Colour Line-by-Line: A single chosen input (RINP, GINP, or BINP) is sampled and multiplexed into
the red channel for processing before being converted by the ADC. The input selected can be
switched in turn (RINP
registers by pulsing the RLC/ACYC pin. This is known as auto-cycling. Alternatively, other sampling
sequences can be generated via the control registers. This mode causes the blue and green
channels to be powered down. Refer to the Line-by-Line Operation section for more details.
To ensure that the signal applied to the WM8141 lies within its input range (0V to AVDD) the CCD
output signal is usually level shifted by coupling through a capacitor, C
WM8141 side of this capacitor to a suitable voltage during the CCD reset level.
A typical input configuration is shown in Figure 5. A clamp pulse, CL, is generated from MCLK and
VSMP by the Timing Control Block. When CL is active the voltage on the WM8141 side of C
RINP, is forced to the VRLC/VBIAS voltage (V
voltage at RINP initially remains at V
to video level) will couple through C
RLC is compatible with both CDS and non-CDS operating modes, as selected by switch 2. Refer to
the CDS/non-CDS Processing section.
GINP
IN
BINP
VRLC
to RINP.
but any subsequent variation in sensor voltage (from reset
RINP…) together with the PGA and Offset DAC control
VRLC
) by switch 1. When the CL pulse turns off, the
IN.
The RLC circuit clamps the
PD Rev 3.0 October 2000
WM8141
IN
, at
11