We used AC transform characteristics to analyze the circuit below and the result as right side. How could we identify the bandwidth of this circuit configuration.
Another circuit configuration, the divided-by-3 constructed before the Vin+, the DC divided-by-3 result could not be met. It seemed that the Vin+ input impedance affected the DUT, could you help do the simulation to clarify the issue? Thank you.
Eric,
The bandwidth of your circuit can be seen by measuring the -3dB point in your response. This is approximately 1.44GHz and 2.35GHz for each circuit respectively.
One thing to note is that the input impedance of the THS3202 is 750kΩ. As you increase the size of the input voltage divider, the input impedance of the amplifier will start to have an effect. Try reducing the size of the input divider to get the same attenuation in your passband. For example, 10kΩ and 20kΩ should be small enough.
Also note that the 5pF at the input is acting as a high pass filter which could be affecting your frequency response if the resistor divider is too large.
Let me know if this resolves your issue.
Regards,Luke LaPointeHigh Speed Amplifiers