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Rakesh

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Posts: 60

Output imepedance
Aug 24^th, 2011, 11:39am

Hi,
I was working on increasing the linearity of the transconductor.
I get a good linearity if i short the output and measure the current.
However if i allow a swing of say peak to peak 400mV on the output my linearity goes down to 60dB .
My output impedance is 400k. Can u suggest me techniques or ways of increasing the output impedance apart from cascoding.
Thanks
Rakesh

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harpoon Senior Member Offline Posts: 112 Hampshire	Re: Output imepedance Reply #1 - Aug 24^th, 2011, 1:17pm Make L bigger ... Or use feedback, I'll have to think about the circuit.
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loose-electron Senior Fellow Offline Best Design Tool = Capable Designers Posts: 1638 San Diego California	Re: Output imepedance Reply #2 - Aug 26^th, 2011, 10:25am gmC filter transconductor? Prior suggestions are good. Also - Increase the static bias current of the device so the signal is a smaller part of the total current. Also differential pair structures can be replaced with multi-tanh structures as gets used in LNA front ends.
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Vladislav D Community Member Offline Posts: 76 The Netherlands	Re: Output imepedance Reply #3 - Aug 27^th, 2011, 4:49am loose-electron wrote on Aug 26^th, 2011, 10:25am: gmC filter transconductor? Prior suggestions are good. Also - Increase the static bias current of the device so the signal is a smaller part of the total current. To increase current through the devices in order to increase output impedance? Sounds controversial....
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loose-electron Senior Fellow Offline Best Design Tool = Capable Designers Posts: 1638 San Diego California	Re: Output imepedance Reply #4 - Aug 28^th, 2011, 12:17pm He is having problems with linearity vs. output impedance. Thus the suggestion on how to improve linearity. If we know the application a bit more may be able to make better suggestions, I am guessing a gmC filter (4 transconductors per biquad) , but it has not been stated.
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