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mpatel74 Post subject: I want to use opamp as a linearizer,Can anyone
help me. Posted: Wed May 17, 2006 10:14 am Lieutenant
Joined: Fri Aug 05, 2005 10:05 pm Posts: 4 Op amp as a linearizer
Top fred47 Post subject: Opamp as linearizerPosted:
Wed May 17, 2006 7:39 pm General Joined: Wed Feb
22, 2006 3:51 pm Posts: 104 Hi! There are two ways of linearizing
a circuit: 1. Feedback - this is especially difficult to add
to an existing circuit at high frequencies, due to the delay around
the loop. 2. Cascading a nonlinear circuit with the circuit which
needs linearization. In this case, you either need to know the shape
of the linearization curve needed, or have some way of measuring the
nonlinearity. In either case, the opamp is not the central item.
Do you have any details that can be shared? Good Luck,
Fred Top IR Post subject: Posted: Thu May 18,
2006 12:01 am Site Admin Joined: Mon Jun 27, 2005
2:02 pm Posts: 373 Location: Germany Hello, Just to
add o Fred's second point: In order to linearize a circuit, you will
need to add the opposite curve to the circuit you want to linearize
(Let's call it DUT), so when you cascade both the outcome is a linear.
This is very common in power amplifiers. For knowing the non-linearity
you need to measure the AM-AM and AM-PM curves, that means the magnitude
and phase behavior of the DUT as function of the input power. Then you
have to synthesize the opposite curves of these at the linearizer circuit.
_________________ Best regards, - IR Top
MLR67 Post subject: Posted: Tue Jun 20, 2006 3:30 pm
Lieutenant Joined: Fri May 12, 2006 11:01 am Posts: 1
Hello , I have just a question I know the problem with feedbak
due to delay , nevertheless in the past (for example in Radar) ,feedback
was used . I know Cherry did a study on this problem. May
you try to explain this problem ? By the way Someone may help me
to find this article Cherry, E.M. and Dabke, K.P., "Transient
Intermodulation Distortion—Part 2: Soft Nonlinearity," J. Aud. Eng.
Soc, 34:1/2, Jan/Feb 1986, pp. 19—35. Top fred47
Post subject: Feedforward linearizationPosted: Tue Jun 20, 2006
6:40 pm General Joined: Wed Feb 22, 2006 3:51 pm
Posts: 104 Hi! There are two kinds of feedback: 1. the normal
kind, where a fraction of the signal itself is fed back to the input
of a circuit, and 2. the corrector/linearizer kind, where the output
itself isn't fed back, just some information about the system performance,
to allow an adaptive circuit to adapt. This doesn't require the bandwidth
of normal feedback. The classic book on the subject is Adaptive Inverse
Control by B. Widrow. The term "transient intermodulation distortion"
came from the audio power amplifier world, where people discovered that
listeners could distinguish between two theoretically-identical amplifiers.
Those amplifiers had identical frequency responses and steady-state
distortion values. This ability to distinguish amplifiers puzzled
many people, and eventually the dynamic behavior of the amplifiers came
to be known as the cause. With large amounts of negative feedback, internal
signals became large enough to cause clipping - and the beneficial effects
of negative feedback were lost. This is probably going to become
more significant in the RF world, as more noise-like signals (such as
CDMA and OFDM) are used. These signals have a large peak-to-average
ratio, so intermittent clipping is more likely than with more classical
signals. I don't have access to Cherry's article, but "soft nonlinearities"
usually refers not to clipping but to active device saturation.
Good Luck! Fred
Posted 11/12/2012
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