HD49338F_15 Datasheet, PDF (8/25 Pages) Renesas Technology Corp – CDS/PGA & 12-bit A/D Converter

HD49338F/HF
Internal Functions
Functional Description
CDS input
CCD low-frequency noise is suppressed by CDS (correlated double sampling).
The signal level is clamped at 56 LSB to 304 LSB by resister during the OB period.
Gain can be adjusted using 10 bits of register (0.033 dB steps) within the range from –2.36 dB to 31.40 dB. *¹
ADC input
The center level of the input signal is clamped at 2048 LSB (Typ).
Gain can be adjusted using 10 bits of register (0.00446 times steps) within the range from 0.57 times (–4.86 dB) to
5.14 times (14.22 dB). *¹
Y-IN input
The input signal is clamped at 280 LSB (Typ) by SYNC Tip clamp.
Automatic offset calibration of PGA and ADC
DC offset compensation feedback for CCD and CDS
Pre-blanking
CDS input operation is protected by separating it from the large input signal.
Digital output is fixed at 32 LSB.
Digital output enable function
Note: 1. Full-scale digital output is defined as 0 dB (one time) when 1 V is input.
Operating Description
Figure 1 shows CDS/PGA + ADC function block.
ADCIN
CDSIN
C2
C1
SH
AMP
VRT
CDS
AMP
PG
AMP
Gain setting
(register)
Current
DAC
12-bit
ADC
D0 to D11
Offset
DAC
calibration
logic
Clamp data
(register) DC offset
feedback
logic
BLKFB
C3
BLKSH
BLKC
C4
OBP
Figure 1 HD49338F/HF Functional Block Diagram
1. CDS (Correlated Double Sampling) Circuit
The CDS circuit extracts the voltage differential between the black level and a signal including the black level. The
black level is directly sampled at C1 by using the SPBLK pulse, buffered by the SHAMP, then provided to the
CDSAMP.
The signal level is directly sampled at C2 by using the SPSIG pulse, and provided to CDSAMP (see figure 1). The
difference between these two signal levels is extracted by the CDSAMP, which also operates as a programmable
gain amplifier at the previous stage. The CDS input is biased with VRT (2 V) during the SPBLK pulse validation
period. During the PBLK period, the above sampling and bias operation are paused.
Rev.2.00 May 20, 2005 page 6 of 22