ICS1531 Data Sheet - Preliminary
Chapter 2
Summary
Chapter 2 Summary
2.1
Overview
The ICS1531 addresses stringent display system line-locked applications by providing clock signals and
digitized pixel data through internal high-performance analog-to-digital converters (ADCs). The ICS1531 is
a complete solution for capturing analog red, green, and blue (RGB) signals from personal computers and
workstations. It supports data capture for resolutions from VGA (640
×
480) to UXGA (1600
×
1200). The
ICS1531 features are described in the following sections.
2.2
Clamp, Video Amplifier, and Analog-to-Digital Circuits (Condition RGB Inputs)
For the following circuits, see
Figure 4-3.
2.2.1
Clamp Circuits (Adjust RGB Inputs to ADC Range)
To properly digitize incoming RGB analog signals, the ICS1531 must adjust the signals to the range of the
ADC. This adjustment is done by clamping the signal, which both (1) establishes a bottom voltage limit and
(2) offsets the signal to align the black level of the incoming signal with the bottom voltage limit. Then the
signal is amplified to adjust the top limit to the upper range of the ADC.
The ICS1531 incorporates an internal clamping circuit to generate a clamping signal. Optionally, the
CLAMP pin can be used to input an externally generated clamp signal (Reg 30:2). In either case, the
polarity of the signal to a clamp can be programmed (Reg 30:3). Typically, the clamp signal is generated by
ADCSYNC (the recovered HSYNC timing pulse). The clamp signal is generated during a non-display
region of time, when most PC display controllers output a black signal.
2.2.2
Video Amplifier Circuits (Amplify RGB Inputs)
The ICS1531’s video amplifier circuit can directly accept analog RGB input signals from a PC display
controller (that is, no external pre-amplifier is required). The video amplifier circuit has three independent
500-MHz video amplifiers for the RGB inputs. To adjust the top level of the signal, this video amplifier circuit
can be programmed for a gain of 1.0, 1.2, 1.4, or 1.6 (Regs 31:1-0, 32:1-0, and 33:1-0). As a result, the
video amplifier circuit can improve low-amplitude signals and adjust analog input signals for the optimum
sampling range of the ADC circuit.
2.2.3
Analog-to-Digital Circuits (Digitize RGB Inputs)
The ICS1531 has high-performance analog-to-digital converters (ADCs) to capture and digitize analog
RGB data (Reg 30:7). Low-power CMOS technology is used to create 8-bit ADCs, which are calibrated to
align the capture event between (1) the 3 analog input channels and (2) either 3 or 6 digital output
channels. The ADC can provide (through Reg 30:6) one of the following:
•
Two 24-bit pixels aligned to a half-rate pixel clock (two-pixels-per-clock mode), which can be used for
48-bit interface panels and image-scaling chips
•
One 24-bit pixel aligned to a full-rate pixel clock (one-pixel-per-clock mode), which can be used for
24-bit-per-pixel applications
In addition, programmable digital-to-analog converters for the R, G, and B inputs fine-tune VRTR, VRTG,
and VRTB, the individual R, G, and B maximum reference ‘top’ voltages (Regs 34-36).
ICS1531 Rev N 12/1/99
Copyright © 1999, Integrated Circuit Systems, Inc.
All rights reserved.
4
December, 1999
ICS [ INTEGRATED CIRCUIT SYSTEMS ]
