Sunday, June 10, 2018

118.5MHz amp Playing with the designer and simulator

In my previous post I offered some programs to help with the design. I will do a couple of quick and dirty examples. Using transistor amp.

 You open the program and click new amp and select the type. Just fill in the blanks. Select the transistor from the list and select the resistor series. For low frequency amps I would use E12. You can get an E12 kit at a reasonable price and get by with low frequency amps. For a high frequency amp the part values become more critical so I go with the E96 series for our high frequency amp. Click ok.
That's all there is to it, until we start Z matching. I set Zin and Zout to 50k for the example. Note the odd value resistors, 49900, 11800 and 162. That's the E96 series values. You can run the sim and change the values to see how critical they are.
With the Zin and Zout at 2k the values are a lot different. I would go with this one over the first because it will be harder to over load. Remember a low Z feeding a high Z will not load up. A high Z feeding a low Z will load up. With less than 2 ma it doesn't cost much.
I did a simple circuit to see the difference. This circuit would be more temperature sensitive. It is still the one I go with more often than not
I 'built' the circuit in the simulator. 1 mv in 80 mv out is not bad?

I put in a second stage to see how it worked. 1 mv to 800 mv?
If you build this circuit in sim change the values of  L1 and L2 to see their effect.

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