WM8253

Production Data

w

PD, Rev 4.1, August 2011

11

TIMING CONTROL

S/H

4-BIT

RLC DAC

CL

+

+

-

TO OFFSET DAC

RLC

CDS

FROM CONTROL

INTERFACE

S/H

V

S

R

S

FROM CONTROL

INTERFACE

MCLK

VSMP

INPUT SAMPLING

BLOCK

CDS

C

IN

VINP

VRLC/

VBIAS

2

1

EXTERNAL VRLC

VRLCEXT

Figure 4 Reset Level Clamping and CDS Circuitry

Reset Level Clamping is controlled by register bit RLCINT. Figure 5 illustrates the effect of the

RLCINT bit for a typical CCD waveform, with CL applied during the reset period.

The RLCINT register bit is sampled on the positive edge of MCLK that occurs during each VSMP

pulse. The sampled level, high (or low) controls the presence (or absence) of the internal CL pulse on

the next reset level. The position of CL can be adjusted by using control bits CDSREF[1:0] (Figure 6).

Figure 5 Relationship of RLCINT, MCLK and VSMP to Internal Clamp Pulse, CL

The VRLC/VBIAS pin can be driven internally by a 4-bit DAC (RLCDAC) by writing to control bits

RLCV[3:0]. The RLCDAC range and step size may be increased by writing to control bit

RLCDACRNG. Alternatively, the VRLC/VBIAS pin can be driven externally by writing to control bit

VRLCEXT to disable the RLCDAC and then applying a d.c. voltage to the pin.