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App notes
> Video
Circuits > APP 4836

Feb 08, 2011

Keywords: portable, battery operated,
single-supply circuitry, op amps, level shifters
Related
parts

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APPLICATION NOTE 4836

Single-supply op amp forms noninverting level
shifter

Abstract: Single-supply
circuitry saves space and cost, but audio and video are
usually referenced to ground, which requires two op amps and a
negative rail. This circuit, however, uses only one op amp
(MAX4380) to level-shift a ground-referenced signal while
operating on a single supply voltage.

Attend
this brief webcast by Maxim on
TechOnline

A
similar version of this article appeared in the May 5, 2010
issue of Electronic Design magazine.

As portable
battery-operated devices continue to shrink in size while
adding functionality, their PCB
real estate becomes increasingly valuable. Single-supply
circuitry can help by saving space and cost. Adding audio or
video, however, can pose a problem because those signals are
usually referenced to ground.

Most single-supply ICs
must be configured for signals above ground, so it's necessary
to shift most audio or video input signals to an appropriate
level above ground. For video, you must also preserve the
signal polarity. Unfortunately, however, operation on a single
supply voltage while preserving signal polarity is impossible
with traditional op-amp level shifters, which demand two op amps
and a negative rail.

The single op-amp circuit of
Figure 1 level shifts a ground-referenced signal while
operating on a single supply voltage. The op amp's
noninverting summing configuration creates the level-shifted
output by summing a reference voltage with the input signal. A
standard potentiometer
with a bypass capacitor sets the reference voltage in this
case, but any voltage reference capable of providing enough
bias current
for the op amp and summing resistors will suffice.

Figure
1. This noninverting level shifter operates on a single supply
voltage, with one op amp.

This example also
includes the 75Ω termination resistors required in a standard
video application. Accordingly, the op amp shown features a
small footprint plus the wide bandwidth
necessary for video. Figure 2 shows the circuit in action,
shifting a 10MHz ground-referenced input signal (bottom trace,
blue) by +1.5V (top trace, orange).

Figure
2. The Figure 1 circuit shifts this ground-referenced 10MHz
signal (bottom trace) by +1.5V (top trace).

Related parts

MAX4380

Ultra-Small, Low-Cost,
210MHz, Single-Supply Op Amps with Rail-to-Rail
Outputs and Disable

Free
samples

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Download,
PDF format (61kB)
APP 4836: Feb 08, 2011

AN4836, AN 4836, APP4836,
Appnote4836, Appnote 4836, DI #809

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