WM8224 datasheet(18/50 Pages) CIRRUS

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WM8224

Production Data

PD, Rev 4.2, September 2013

DEVICE DESCRIPTION

INTRODUCTION

A block diagram of the device showing the signal path is presented on the front page of this

datasheet.

The WM8224 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 between one and 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 a 9-bit

Programmable Gain Amplifier (PGA).

The processing channel outputs are switched alternately by a 3:1 multiplexer to the ADC input.

The ADC then converts each resulting analogue signal to a digital word. The digital output from the

ADC is presented in a variety of possible output formats onto the output bus, OP[11:0]. The twelve

output pins can be set to a high impedance state using either the OEB control pin or the OPD register

bit.

On-chip control registers determine the configuration of the device, including the offsets and gains

applied to each channel. These registers are programmable via a serial interface.

The device has a Black-Level Calibration function which allows the D.C. offset determined during the

optically-black pixels at the beginning of the linear sensor to be removed during the image-pixels.

CONFIGURABLE RESOLUTION OF ADC

The WM8224 has a configurable ADC resolution. The default setting is 16 bits resolution. This can

be changed by the user by changing a register setting.

The register RES[1:0] can be changed to alter the resolution from 16 bits to either 12, 10 or 8 bits

resolution.

INPUT SAMPLING

The WM8224 can sample and process up to three inputs through one to 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.

Two Channel Pixel-by-pixel: Two input channels (RINP and GINP, RINP and BINP, or 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 both inputs within the pixel period. The

unused channel can be changed via the control interface. The unused channel is powered down

when this mode is selected.

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 channel can be changed via

the control interface. The unused channels are powered down when this mode is selected.

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