Re: Differential amplifier offset issue


archiees@xxxxxxxxx wrote:
Hi,
I am designing a multiple stage amplifier.
I have a first stage
differential amplifier using JFETs which gives output with a 5 volt
offset on the drain.
Now i want to amplify this signal more, i can't feed it to the
intrumentation amplifier without blocking capacitors. And i want to
avoid using blocking capacitors.
For this reason i was thinking to design another differential stage
using PNP BJTs to amplify as well as DC level shift the signal to 0
volts. Then if needed i can feed this to a instrumentation amplifier.
So currently, i am trying to design a PNP differential stage which can
take 5 volts as the base and collector around 0 volts. I have tried
some simulations in spice but can't get it working.
Can anyone help , please?

The simplest way is to use two resistors, say 50K and 150K in series to
-15 volts.

The center tap will be at zero volts.

You lose a little gain but what the heck.

or use a 5V zener in place of the 50K resistor, no gain lost.

.

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