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Q&A Testing instrumentation amplifier with differential signal

I am using the AD620 as instrumentation amplifier to amplify the body's ECG signal. An ECG is a differential signal (measured with two electrodes) and I want a differential gain of Gd=1000 . The ...

3 answers  ·  posted 1y ago by Carl‭  ·  last activity 1y ago by TonyStewart‭

#3: Post edited by user avatar Carl‭ · 2023-03-11T07:55:17Z (about 1 year ago)
  • I am using the [AD620 ](https://www.analog.com/media/en/technical-documentation/data-sheets/ad620.pdf)as instrumentation amplifier to amplify the body's ECG signal. An ECG is a differential signal (measured with two electrodes) and I want a differential gain of Gd=1000
  • .
  • The datasheet has this formula: $G_d=1+\frac{49.4 \: \text{k}Ω}{R_G}$
  • , so using two resistors of 27 Ω
  • gives me a gain of 916
  • which is good enough.
  • I want to test the amplifier, by generating a 5 mV peak-peak sinusoid, send it into the in-amp and expect around 5 V peak-peak on the output. So I thought of using this setup: -
  • ![Image alt text](https://electrical.codidact.com/uploads/yk6t3829uih4p1kinpfmtpiu63rz)
  • However, my instructor suggests generating a 15 mV peak-peak sinusoid and using this setup instead: -
  • ![Image alt text](https://electrical.codidact.com/uploads/bq5m9tigd1pye5ttsdg27iyo3ig8)
  • He said the setup was for creating a differential signal, but I am not sure why the first setup doesn't work.
  • **Question:** Why is the second setup needed to test my differential amplifier? What does the second setup do that the first one doesn't?
  • I am using the [AD620 ](https://www.analog.com/media/en/technical-documentation/data-sheets/ad620.pdf)as instrumentation amplifier to amplify the body's ECG signal. An ECG is a differential signal (measured with two electrodes) and I want a differential gain of Gd=1000
  • .
  • The datasheet has this formula: $G_d=1+\frac{49.4 \: \text{k}Ω}{R_G}$
  • , so using two resistors of 27 Ω
  • gives me a gain of 916
  • which is good enough.
  • I want to test the amplifier, by generating a 5 mV peak-peak sinusoid, send it into the in-amp and expect around 5 V peak-peak on the output. So I thought of using this setup: -
  • ![Image alt text](https://electrical.codidact.com/uploads/yk6t3829uih4p1kinpfmtpiu63rz)
  • My instructor suggests generating a 15 mV peak-peak sinusoid and using this setup instead: -
  • ![Image alt text](https://electrical.codidact.com/uploads/bq5m9tigd1pye5ttsdg27iyo3ig8)
  • **Question:** Why is the second setup needed to test my differential amplifier? What does the second setup do that the first one doesn't?
#2: Post edited by user avatar Carl‭ · 2023-03-08T17:09:10Z (about 1 year ago)
  • I am using the AD620 as instrumentation amplifier to amplify the body's ECG signal. An ECG is a differential signal (measured with two electrodes) and I want a differential gain of Gd=1000
  • .
  • The datasheet has this formula: $G_d=1+\frac{49.4 \: \text{k}Ω}{R_G}$
  • , so using two resistors of 27 Ω
  • gives me a gain of 916
  • which is good enough.
  • I want to test the amplifier, by generating a 5 mV peak-peak sinusoid, send it into the in-amp and expect around 5 V peak-peak on the output. So I thought of using this setup: -
  • ![Image alt text](https://electrical.codidact.com/uploads/yk6t3829uih4p1kinpfmtpiu63rz)
  • However, my instructor suggests generating a 15 mV peak-peak sinusoid and using this setup instead: -
  • ![Image alt text](https://electrical.codidact.com/uploads/bq5m9tigd1pye5ttsdg27iyo3ig8)
  • He said the setup was for creating a differential signal, but I am not sure why the first setup doesn't work.
  • **Question:** Why is the second setup needed to test my differential amplifier? What does the second setup do that the first one doesn't?
  • I am using the [AD620 ](https://www.analog.com/media/en/technical-documentation/data-sheets/ad620.pdf)as instrumentation amplifier to amplify the body's ECG signal. An ECG is a differential signal (measured with two electrodes) and I want a differential gain of Gd=1000
  • .
  • The datasheet has this formula: $G_d=1+\frac{49.4 \: \text{k}Ω}{R_G}$
  • , so using two resistors of 27 Ω
  • gives me a gain of 916
  • which is good enough.
  • I want to test the amplifier, by generating a 5 mV peak-peak sinusoid, send it into the in-amp and expect around 5 V peak-peak on the output. So I thought of using this setup: -
  • ![Image alt text](https://electrical.codidact.com/uploads/yk6t3829uih4p1kinpfmtpiu63rz)
  • However, my instructor suggests generating a 15 mV peak-peak sinusoid and using this setup instead: -
  • ![Image alt text](https://electrical.codidact.com/uploads/bq5m9tigd1pye5ttsdg27iyo3ig8)
  • He said the setup was for creating a differential signal, but I am not sure why the first setup doesn't work.
  • **Question:** Why is the second setup needed to test my differential amplifier? What does the second setup do that the first one doesn't?
#1: Initial revision by user avatar Carl‭ · 2023-03-08T17:08:43Z (about 1 year ago)
Testing instrumentation amplifier with differential signal
I am using the AD620 as instrumentation amplifier to amplify the body's ECG signal. An ECG is a differential signal (measured with two electrodes) and I want a differential gain of Gd=1000
.

The datasheet has this formula: $G_d=1+\frac{49.4 \: \text{k}Ω}{R_G}$
, so using two resistors of 27 Ω
 gives me a gain of 916
 which is good enough.

I want to test the amplifier, by generating a 5 mV peak-peak sinusoid, send it into the in-amp and expect around 5 V peak-peak on the output. So I thought of using this setup: -

![Image alt text](https://electrical.codidact.com/uploads/yk6t3829uih4p1kinpfmtpiu63rz)

However, my instructor suggests generating a 15 mV peak-peak sinusoid and using this setup instead: -

![Image alt text](https://electrical.codidact.com/uploads/bq5m9tigd1pye5ttsdg27iyo3ig8)

He said the setup was for creating a differential signal, but I am not sure why the first setup doesn't work.

**Question:** Why is the second setup needed to test my differential amplifier? What does the second setup do that the first one doesn't?