
VSP2232
SLAS320
–
MAY 2001
4
www.ti.com
Terminal Functions (continued)
TERMINAL
TYPE
DESCRIPTION
NAME
SLOAD
VCC
Designators in TYPE column: P
–
power supply and ground, DI
–
digital input, DO
–
digital output, AI
–
aAnalog input, AO
–
analog output
NO.
46
DI
P
Serial data latch signal (triggered at the rising edge)
Analog power supply
18, 24, 27, 33, 34, 40
detailed description
introduction
The VSP2232 is a complete mixed-signal IC that contains all of the key features associated with the processing
of the CCD imager output signal in a video camera, a digital still camera, a security camera, or similar
applications. A simplified block diagram is shown on the front page of this data sheet. The VSP2232 includes
a correlated double sampler (CDS), a programmable gain amplifier (PGA), an analog-to-digital converter
(ADC), an input clamp, an optical black (OB) level clamp loop, a serial interface, a timing control, and a reference
voltage generator. We recommend an off-chip emitter follower buffer between the CCD output and the VSP2232
CCDIN input. The PGA gain control, the clock polarity setting, and the operation mode choosing can be made
through the serial interface. All parameters are reset to the default value when the RESET pin goes to low
asynchronously from the clocks.
correlated double sampler (CDS)
The output signal of a CCD imager is sampled twice during one pixel period, one at the reference interval and
the other at the data interval.
Subtracting these two samples, extracts the video information of the pixel as well as removes any noise that
is common
—
or correlated
—
to both the intervals.
Thus, a CDS is very important to reduce the reset noise and the low frequency noises that are present on the
CCD output signal. Figure 1 shows the simplified block diagram of the CDS and input clamp.
_
+
OPA
C(1) = 5 pF
C(2) = 5 pF
SHP
SHD
REFN (1.25 V)
VSP2232
CCDIN
CLPDM
SHP
CIN
CCD
Output
Figure 1. Simplified Block Diagram of CDS and Input Clamp
The CDS is driven through an off-chip coupling capacitor (C
IN
). AC coupling is strongly recommended because
the DC level of the CCD output signal is usually too high (several volts) for the CDS to work properly. A 0.1-
μ
F
capacitor is recommended for C
IN
, however, it depends on the application environment.