Input Amplifier

rickman · 2016-04-05T18:39:25+00:00

I got help from Joerg some time back with an amplifier for an antenna signal for WWVB at 60 kHz. I was looking at a version in LTspice and noticed the bypass cap on the source leg of the second stage was a lot smaller than the others doing a similar job. It was reducing the gain of the second stage a bit and I increased it from 3.3 nF to 33 nF. Oddly enough, it dropped the gain of the first stage about the same amount it increased the gain of the second stage. At first I thought it might be something to do with loading the first stage output with increased capacitance, but I can't see how that would be right. So I'm thinking it has more to do with just the loading of the first stage by a different input impedance on the second stage, but I can't convince myself of this either, it's a JFET, not a bipolar transistor. So what is going on? Here's the schematic I'm simulating... Version 4 SHEET 1 1940 680 WIRE 1008 -384 1008 -416 WIRE 816 -288 816 -336 WIRE 1008 -256 1008 -304 WIRE 1136 -256 1008 -256 WIRE 1440 -256 1136 -256 WIRE 1008 -224 1008 -256 WIRE 1440 -224 1440 -256 WIRE 816 -160 816 -208 WIRE 816 -160 704 -160 WIRE 896 -160 816 -160 WIRE 960 -160 896 -160 WIRE -48 -144 -96 -144 WIRE 48 -144 -48 -144 WIRE 48 -128 48 -144 WIRE 368 -128 368 -160 WIRE 816 -128 816 -160 WIRE 1440 -128 1440 -160 WIRE -96 -112 -96 -144 WIRE 704 -112 704 -160 WIRE 1008 -32 1008 -128 WIRE -96 -16 -96 -32 WIRE 48 -16 48 -64 WIRE 704 -16 704 -48 WIRE 816 -16 816 -48 WIRE 816 -16 704 -16 WIRE 368 0 368 -48 WIRE 416 0 368 0 WIRE 480 0 416 0 WIRE 640 0 544 0 WIRE 816 16 816 -16 WIRE 368 32 368 0 WIRE 1008 32 1008 -32 WIRE 240 96 -16 96 WIRE 320 96 240 96 WIRE 640 96 640 0 WIRE 832 96 640 96 WIRE 960 96 832 96 WIRE 240 144 240 96 WIRE 368 144 368 128 WIRE 448 144 368 144 WIRE 496 144 448 144 WIRE 1008 144 1008 128 WIRE 1088 144 1008 144 WIRE 1136 144 1088 144 WIRE -16 160 -16 96 WIRE 368 176 368 144 WIRE 640 176 640 96 WIRE 1008 176 1008 144 WIRE 496 192 496 144 WIRE 1136 192...

Input Amplifier

Apr 05, 2016 43 Replies

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Ian Field 10 years ago

Dual gate MOSFETs are a ready made, all in one package casc_o_de, and they're not quite as bad as JFETs for all over the place parameter spreads.

In most cases, you can set Id to whatever you want with the potential applied to G2.

MOSFETs liberated from a TV tuner have very low capacitance - especially from a UHF tuner.

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Joerg 10 years ago

120kHz, how precise depends on the model. It is the poor choice of protocol (on-off AM) and the bandwidth that makes it unreliable. Not worth it and I had to learn it the hard way. If you don't build it yourself home automation is either really expensive or unreliable. De facto it mostly does not exist.

Regards, Joerg http://www.analogconsultants.com/

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Joerg 10 years ago

They are usually not very happy at 2.2V supply though.

Regards, Joerg http://www.analogconsultants.com/

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legg 10 years ago

Non-functional with default part.

I added the BF862 model into 'standard.jft' file and it biased with gain, using the BF862. .ac gives poor passband definition, when functional.

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