WM8259

Production Data

w

PD Rev 4.2 April 2007

11

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.

CDS/NON-CDS PROCESSING

For CCD type input signals, the signal may be processed using CDS, which will remove pixel-by-pixel

common mode noise. For CDS operation, the video level is processed with respect to the video reset

level, regardless of whether RLC has been performed. To sample using CDS, control bit CDS must

be set to 1 (default), this controls switch 2 (Figure 4) and causes the signal reference to come from

programming control bits CDSREF[1:0], as shown in Figure 6.