8

Application Circuit #1

Figure 1 shows a very high speed RGB (or YUV) multiplexer.

Two video sources can be displayed on one monitor with the

only stipulation that the video sources have to be

synchronous. An example is a picture-in-picture, or “window”

is generated with one video source (e.g. RGB TV) in a

window, and a computer application around it. Multiplexing

synchronous RGB signals has the advantage that the video

signals do not have to be digitized, and an image stored in

RAM prior to being displayed.

When the monitor is switched off, or goes into its power-

saving blanked mode, the EL4331 can be powered down to

further save power. The input impedance does not change

appreciably between powered up and down modes, although

the bias current does drop to near zero.

A demonstration board with this circuit on it is available from

Elantec.

Application Circuit #2

Figure 2 shows a circuit that has either a very wide

bandwidth, or an 11MHz low pass response. The EL4331’s

“A” inputs are connected to the one frequency determining

set of components, while the “B” inputs are connected

directly. The A/B select pin therefore selects the desired

bandwidth. This would allow appropriate filtering to clean up

noisy low bandwidth video signals when displaying them on

a high quality wide bandwidth monitor.

Application Circuit #3

Figure 3 shows one of the three channels of a component

video, 8:1 multiplexer. The A/B select pins naturally allow

binary coded addressing—allowing simple microprocessor

or state machine control. Note that each amplifier output is

loaded, to keep the amplifier outputs damped.

Photograph A1 shows a staircase generated by having all

the inputs (sig0 through sig7) connected to a resistive divider

chain, and the select bits were driven by a binary counter.

Photograph A2 shows the glitch between steps 4 and 5; this

is the worst glitch since all three banks of EL4331s are

switching together. The magnitude of this glitch is affected by

the timing skew of the select lines, the physical length of the

traces, and the difference in amplitude of the two signals.

This particular circuit was bread-boarded using EL4331s on

their adapter boards (available from Elantec for those who

can not breadboard with SOICs), and the binary counter was

an 'LS163.

FIGURE 1. TWO RGB SOURCES MULTIPLEXED TO ONE

RGB OUTPUT

FIGURE 2. A BANDWIDTH-SELECTABLE FILTER

EL4331