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Lambda diode applications #1

Use to boost the bandwidth of a gyrator, used here in a rob-Peter-to-pay-Paul high-pass filter configuration

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Reply to
bitrex
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On a sunny day (Mon, 8 Jul 2019 03:38:33 -0400) it happened bitrex wrote in :

I think this is not right, if you really used he negative resistance aspect it would increase Q and decrease bandwidth. I think you are merely damping the circuit, causing it so see a lower R and thus increasing frequency and bandwidth at that.

Reply to
Jan Panteltje

if it were also behaving as just a strictly a linear resistor equivalent to R3 on the right, but a smaller value, the phase shift above ~1k would also be monotonic decreasing, I don't believe it could break down and then break back up again in this RL-highpass equivalent configuration as it does.

Reply to
bitrex

The circuit is bizarre and wrong in more ways than I have time to enumerate.

--

John Larkin   Highland Technology, Inc   trk 

jlarkin att highlandtechnology dott com 
http://www.highlandtechnology.com
Reply to
John Larkin

or rather, the phases are both monotonic decreasing but there couldn't be an inflection point

Reply to
bitrex

a Convincing analysis...

Reply to
bitrex

On a sunny day (Mon, 8 Jul 2019 10:55:22 -0400) it happened bitrex wrote in :

I am not questioning the circuit does what it does (according to spice). See what I wrote. But you also use a signal from the PNP emitter, so not really a 2 pole lambda thing.

If what it does is what you wanted it to do, then that is great. But I think it does not make a good example of using a lambda diode.

Reply to
Jan Panteltje

If I remove the signal entirely and just apply a bias voltage for V3. Ramp the bias voltage between about 2 and 8 volts. The current that V3 sources increases linearly. The current that op amp U1 sinks also increases, and is approximately the same current that V3 is sourcing, since the output is servoed to 0 volts by U3 and its input draws no current from the output.

So the bias current increases from 0.2 mA to almost 1 mA as the DC bias voltage is increased. That current can only pass thru the lambda diode structure. meanwhile the voltage drop across the structure stays approximately constant thru that range.

If the current forced thru it is increasing but the drop across it is staying approximately constant then its equivalent impedance must be decreasing with increasing bias current.

basically IMO it's a valid use for the structure to fiddle the bias such that it's operating not over into the negative resistance region but around the peak of the curve, so it's acting like a current-controlled resistance. at high freq the impedance of the equivalent of R3 on the right gets boosted and at low it gets reduced. but the impedance there also affects the nominal inductance value of the virtual "inductance" too, unfortunately, which explains the sloppy phase shift trace, looks like it's "robbing" phase from the left side to give to the right.

Reply to
bitrex

Basically, try experimenting with R3 in the standard gyrator on the right, which sort of the defines the "ESR" of your equivalent inductance in the RL high pass.

Increase the value to 1k and see how the response on the high end improves but you get f***ed on low end, lower it to 50 and vice-versa. circuit on left is a compromise

Reply to
bitrex

No, you're correct somethings not right, it's not biased correctly to do what I claim - it's acting too much like a linear resistor as it's currently biased.

Reply to
bitrex

Scratch my followups, it wasn't operating the way I thought it was. The low-frequency response should be approximately the same. The idea is to use the cusp of the lambda diode curve where the equivalent resistance has a horizontal tangent to boost the impedance looking into the gyrator at high frequency and extend the HF response, something like this:

I haven't found the best operating point yet, though.

Reply to
bitrex

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