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What is the noise factor of ad8338?

• Hi rookie1,

The Noise Factor will depend on the source impedance and also on the gain setting used. Here is an example calculation for AD8338 at maximum gain:

https://en.wikipedia.org/wiki/Noise_figure

F= 1 + Na / (Ni * G)

Na = Output referred noise power (amplifier related)

G = Power Gain

Ni = Input noise power

Assuming Vgain = 1.1V --> 80dB voltage gain (Node Pin High) --> output referred noise = 45,000nV/RtHz --> Na = 2.03e-9 V^2/Hz

Assuming a source resistance of 50ohm --> Ni = (0.91nV/RtHz)^2 = 8.28e-19 V^2/Hz

G = (10,000) ^2 = 1e8 V^2/V^2

F = 1 + 2.03e-9 / (8.28e-19 * 1e8) = 25.4

NF = 10*log(25.4) = 14.1dB

Assuming I've not made any mistakes along the way!

You can do your calculation based on the actual gain and input / source resistance accordingly.

Regards,

Hooman

• Hi,

Your answer is very helpful. I have one more question. Could you please tell me how to connect VAGC pin without using AGC feature of AD8338?

• Hi rookie1,

You're welcome! :-)

Regarding your additional question on AD8338: "Could you please tell me how to connect VAGC pin without using AGC feature of AD8338?"

Datasheet page 5 states: "If the AGC feature is not used, tie VAGC to VREF".

Regards,

Hooman

• Hi,

Thank you very much for your reply. According to your answer, this is the single-ended input circuit diagram after I connected it. Is there any problem?My input signal frequency is around 1kHz to 20kHz.Looking forward to your reply.

Regards

• Hi Rookie1,

Using 100uF polarized capacitors works well in simulations, but are not very practical or necessary for a 1kHz AC coupling.  Take a look at the eval board user guide for some practical values:

https://www.analog.com/media/en/technical-documentation/user-guides/UG-559.pdf

Otherwise, I think you're connecting the part up as recomended:

PB

• Hi prb,

OK, I see. What capacitance should I change to?I compared them. Is there anything wrong with the circuit diagram?

Regards,

rookie

• Hi hooman,
Can the AD8338 single end output and how should it be operated?
Dangling or something?
regards,
rookie1