EL4331

FN7162 Rev 1.00

Page 8 of 10

May 12, 2004

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