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I would like to use this buffer suggested by a user named MOSFET from a previous post I made (Why is buffer output signal reduced to half?).

schematic

Image source: Answer to "Why is buffer output signal reduced to half?" by MOSFET posted on Electrical Engineering Stack Exchange and licensed under CC BY-SA 4.0.

I will try to be as detailed as I can here since I have not in the previous posts. I want to design a buffer for a Hartley oscillator which I plan to make operate at 500 MHz. I want the output of the swing oscillator to be 1V peak to peak. Then I want to pass this through a buffer where the output should stay 1V peak to peak. This buffer is for isolation to prevent the 50 ohm measurement instrument from loading the oscillator.

For the sake of providing details, let us say I want the power supply to be 2.5V. The current through the transistors 1mA. This means the DC power should be 2.5mW. Will this buffer work if use appropriate transistor with high fT (8 GHz for example)?

Here is the schematic on LT SPICE. I am not getting sensible results.

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    \$\begingroup\$ What is preventing you from simulating this circuit and finding out yourself? \$\endgroup\$
    – Andy aka
    Commented May 2 at 16:43
  • \$\begingroup\$ i simulated it. didn't work... \$\endgroup\$
    – xcaliber99
    Commented May 2 at 18:45
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    \$\begingroup\$ I get the impression that you haven't used a simulator before. If so, then learning to use one should be regarded as a more pressing need than this particular question. Simulating over 270 ps is pointless. \$\endgroup\$
    – Andy aka
    Commented May 2 at 18:48
  • \$\begingroup\$ 1. Increase V1 from 2.5V to 5V. 2. Show the input voltage V2 as well as the output. 3. Change R3 from 50 to 1k. Try these changes to get understanding before trying the values you want in your final circuit. \$\endgroup\$
    – Fabio Barone
    Commented May 2 at 18:48
  • \$\begingroup\$ nah that didn't do anything. the problem must be something else. \$\endgroup\$
    – xcaliber99
    Commented May 2 at 19:13

1 Answer 1

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Added a 39 Ohm resistor to raise the output impedance to 50 Ohm. Voltage gain is 0.5.

Input impedance without considering package (or other) parasitics:

400 Ohm || 1.2pF @ 100MHz

330 Ohm || 1.2pF @ 500MHz

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