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want to know
Joined: 12 Sep 2006
Posts: 11
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 12 Sep 2006 5:22 some questions about limiting amplifier |
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| when design a limiting amplifier, what is the most important thing? gain flatness? output power flatness? the distortion of the phase?
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G4BCH
Joined: 10 May 2006
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12 Sep 2006 12:59 Re: some questions about limiting amplifier |
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All of them.
It depends on what paramters are most important to your system.
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want to know
Joined: 12 Sep 2006
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13 Sep 2006 7:00 Re: some questions about limiting amplifier |
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| OK! But are there any books or articles talk about limiting amplifiers? The microwave books I have read don't relate to it, even though there are details about LNA, PA. Can you give me some suggestions?
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G4BCH
Joined: 10 May 2006
Posts: 100
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13 Sep 2006 8:12 Re: some questions about limiting amplifier |
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I've only seen a few articles on limiting amplifiers, and they were writen by people who make them so the technical details were sketchy at best.
You are unlikely to find much in the text books, they usually only deal in linear circuits and as you know a limiter is about as non-linear as you can get.
What frequency range & dynamic range are you trying to cover?
If you just need a constant ampitude output then a multistage ampifier with controlled small signal gain amplifier stages is probably your best bet. Most limiters I've seen have about 10dB or so per stage.
If you have CAD software with non-linear modeling, ie SPICE, harmonic balance etc you can try modwlling your circuit, but from my experience the results are only a rough guide much above 1dB compression point.
Peter
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want to know
Joined: 12 Sep 2006
Posts: 11
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14 Sep 2006 10:16 Re: some questions about limiting amplifier |
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You are so good to give me so much advice. I'm troubled by a limitng amplifier. Its output power should be much less than the normal output power when the input signal power is 5 dB smaller than the input power range. So it need good small signal gain flatness and the P1dB of latest stage should be changed little at different frequency. It is difficult to achieve.
In my idear the limiting amplifier just need to have good output power flatness and little distortion. So I want to know how the performance of the limting amplifier influence the system!
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G4BCH
Joined: 10 May 2006
Posts: 100
Helped: 28
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15 Sep 2006 8:23 Re: some questions about limiting amplifier |
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Only you know what your system is so only you can answer the queation as to how the limiter will affect it.
You say you want little distortion, the whoe idea of a limiter is to introduce distortion. If you mean that you want a sinusoidal output then you can only acheive that over less than an octave where you can use filters to reduce the second and greater harmonics. If you are working over greater than an octave the best you can hope for is to use a symetric limiter an reduce the even harmonics giving you a squarewave ouput. The above assumes a single sigal input, for multiple input signals the all bets are off on distortion unless one is greater than the sum of rest, then it will capture.
As to amplifer design, yes it can be tricky. particulalry if you are using the amplifier as a limiter. You can't rely on the linear S-parameters supplied by the vendor as you are using the device outside its normal operatiing conditons. If you need the data for design you have to measure it yourself, and even then you are shooting at a moving target, you need good small signal and large signal performance.
Peter
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