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| OpAmp OPA835 single rail design |
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| raff5184:
Hi all, I'm trying to design an amplification circuit using an OPA835. My input signal is a 150kHz 0-5mV signal (or -5mV-0 depending on the configuration I use). I want a voltage gain of 600x (56dB), or the best I can have with single rail supply, powering the opamp with a 3.8V 500mAh battery. Fig.17 of the datasheet tells me that at 150kHz my gain is around 40-45dB, at best. Let's assume that it is fine. I did a simple inverting configuration, and chose R_F=2kOhm as specified on page 31 of the datasheet and, consequently, R_G =3 Ohm. But I don't see any amplification of AC signals on the output. Is it ok to chose the two resistors the way I did? Thank you |
| Zero999:
Please post a schematic. To use a single supply, the op-amp must be AC coupled with capacitors. |
| Audioguru again:
Why do you select an inverting amplifier? Since the frequency peaking is reduced when the Rf resistor is only 2k then the input resistor value must be very low for a high gain. Then the input source impedance must be extremely low. Here is your amplifier: |
| raff5184:
This is the circuit. I followed the TI manual http://www.ti.com/lit/an/sloa030a/sloa030a.pdf Case 1 page 8. The problem I have with this circuit is that it is already saturated and I measure a DC value of 3.7V |
| raff5184:
--- Quote from: Audioguru again on September 17, 2019, 04:20:34 pm ---Why do you select an inverting amplifier? Since the frequency peaking is reduced when the Rf resistor is only 2k --- End quote --- Simply because it is mostly recommended, but honestly I'm not sure when it is fine to use a non-inverting design. Is there a rule of thumb? However, I used a non-inverting one. |
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