My customer has a question about using differential Amplifier drive circuits (using THS4509) for dc-coupled.
I went through the circuit based on Figure 88 on the datasheet.(See Attachment)Do you have any problems with this circuit?
Best regards, H.Katsunaga
You mention needing DC coupling, is this just on the output of the amplifier or does the customer need DC coupling from input to output? In the circuit you have shown, the amplifier will set the common-mode voltage at the ADC input pins instead of biasing them through resistors, however it will not pass a DC signal from the input source to the ADC. It will not pass low frequency signals because of the 0.1 uF capacitors on the negative and positive pins of the amplifier. Is this okay for the customer or will their input have a DC signal that needs to be passed?
And what is their signal source? What are the signal levels (DC and amplitude)? What is the frequency range of the input? How much gain is needed?
Thank you for your responses.
I got more information for my customer's circuits.
Please see New Attachment.
Do you have any problems with this circuit?
1.The customer needs DC coupling from input to output.
2.DC level of signal source is 1V. Amplitude of signal source is -8dBm. and Rs is 50Ohm.
3.The Frequency range is 35kHz to 6MHz.
4.The differential Amplifier Gain is 0dB. And the differential Amplifier isn't THS4509. It sounds making a selection.
This circuit looks better. I beleive there will need to be some sort of biasing on the positive input pin to keep the proper DC levels. You can play with this in any spice program to see the result. For instance, split the resistor RS//RT into a reistor divider to give the proper DC bias on the positive pin and the parallel combination still equals RS//RT. I'm not an amp expert, so I can't offer much more help than that.
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