Production Data

WM8214

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PD Rev 4.1 March 2007

13

DEVICE DESCRIPTION

INTRODUCTION

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

datasheet.

The WM8214 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 ADC then converts each resulting analogue signal to a 16-bit digital word. The digital output from

the ADC is presented on an 8-bit wide bus.

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 WM8214 has been designed to have a high degree of compatibility with previous generations of

Wolfson AFEs.

By setting the LEGACY register bit the device adopts the same timing as the

WM819x and WM815x families of AFEs. The control interface is also compatible.

INPUT SAMPLING

The WM8214 can sample and process one 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) 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 Blue 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 and channel can be changed

via the control interface, e.g. on a line-by-line basis if required. The unused channels are powered

down when this mode is selected.

Colour Line-by-Line: A single input (RINP) is sampled and multiplexed into the red channel for

processing before being converted by the ADC. The registers which are applied to the PGA and

Offset DAC can be switched in turn (RINP

→ GINP → BINP → RINP…) by applying pulses to the

RSMP pin. This is known as auto-cycling. Alternatively, other sequences can be generated via the

control registers. This mode causes the unused blue and green channels to be powered down. Refer

to the Line-by-Line Operation section for more details.