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Differential input and output op-amps. When do you use them?

M

mook johnson

Jan 1, 1970
0
I tend to keep things single ended and only on rare occasion have I
resorted to a differential analog signal.

When interfacing to a 16+ bit ADC with differential inputs. Then I'll
generally make the entire circuit differential as far up as practical to
the sensor.

Also when the signal has to travel through a wiring harness or pass a
noisy part of the board.

I have also played games with psudo-differential with those types of
input where a dedicated signal reference trace parallel to the feed
trace (or twisted pair) from the "-" input to the local source "ground"
when the performance is not THAT critical.

Are there any other places where a differential signal is key to getting
the performance and cannot be achieved readily with single ended?
 
W

whit3rd

Jan 1, 1970
0
I tend to keep things single ended and only on rare occasion have I
resorted to a differential analog signal.
Are there any other places where a differential signal is key to getting
the performance and cannot be achieved readily with single ended?

If you are concerned with distortion of signal on long transmission lines,
and pickup/radiation, differential is preferred.

Long lines, before 1950, meant a few miles.
In 1970, long lines were a few meters.
In 2013, long lines are a few centimeters.
 
M

miso

Jan 1, 1970
0
I tend to keep things single ended and only on rare occasion have I
resorted to a differential analog signal.

When interfacing to a 16+ bit ADC with differential inputs. Then I'll
generally make the entire circuit differential as far up as practical to
the sensor.

Also when the signal has to travel through a wiring harness or pass a
noisy part of the board.

I have also played games with psudo-differential with those types of
input where a dedicated signal reference trace parallel to the feed
trace (or twisted pair) from the "-" input to the local source "ground"
when the performance is not THAT critical.

Are there any other places where a differential signal is key to getting
the performance and cannot be achieved readily with single ended?

In leapfrog (ladder) active filter (i.e. continuous time) design, you
can use a differential output rather than add inverting stages.
 
I tend to keep things single ended and only on rare occasion have I

resorted to a differential analog signal.



When interfacing to a 16+ bit ADC with differential inputs. Then I'll

generally make the entire circuit differential as far up as practical to

the sensor.



Also when the signal has to travel through a wiring harness or pass a

noisy part of the board.



I have also played games with psudo-differential with those types of

input where a dedicated signal reference trace parallel to the feed

trace (or twisted pair) from the "-" input to the local source "ground"

when the performance is not THAT critical.



Are there any other places where a differential signal is key to getting

the performance and cannot be achieved readily with single ended?

Yes, almost anything that involves a sensor. Anywhere you need to reduce noise which is just about anywhere. One amp to another etc. Strain guages etc
 
If you use a single-ended amp with the standard 4 resistor network for accepting diff inputs, then the impedance seen at the plus and minus inputs are are different for common-mode signals versus diff signals. A diff amp can solve this


Bob
 
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