I Want to Use Opamp as a Linearizer, Can Anyone Help Me - RF
Post subject: I want to use opamp as a linearizer,Can
anyone help me. Posted: Wed May 17, 2006 10:14 am
Joined: Fri Aug 05, 2005 10:05 pm
Op amp as
Post subject: Opamp
as linearizerPosted: Wed May 17, 2006 7:39 pm
Joined: Wed Feb 22, 2006 3:51 pm
There are two ways of linearizing a circuit:
- this is especially difficult to add to an existing circuit at
high frequencies, due to the delay around the loop.
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?
Post subject: Posted: Thu May 18, 2006
Joined: Mon Jun 27, 2005
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
Post subject: Posted: Tue Jun 20,
2006 3:30 pm
Joined: Fri May 12, 2006
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.
Post subject: Feedforward
linearizationPosted: Tue Jun 20, 2006 6:40 pm
Joined: Wed Feb 22, 2006 3:51 pm
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,
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.