Because of the high maintenance needed to monitor and filter spammers from the RF Cafe Forums, I decided that it would
be best to just archive the pages to make all the good information posted in the past available for review. It is unfortunate
that the scumbags of the world ruin an otherwise useful venue for people wanting to exchanged useful ideas and views.
It seems that the more formal social media like Facebook pretty much dominate this kind of venue anymore anyway, so if
you would like to post something on RF Cafe's
page, please do.
Below are all of the forum threads, including all
the responses to the original posts.
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 a linearizer
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
1. Feedback - this is especially difficult to add
to an existing circuit at high frequencies, due to the delay around
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?
Post subject: Posted: Thu May 18,
2006 12:01 am
Joined: Mon Jun 27, 2005
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.
Post subject: Posted: Tue Jun 20, 2006 3:30 pm
Joined: Fri May 12, 2006 11:01 am
I have just a question I know the problem with feedbak
due to delay , nevertheless in the past (for example in Radar) ,feedback
I know Cherry did a study on this problem.
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.
Post subject: Feedforward linearizationPosted: Tue Jun 20, 2006
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, 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
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
I don't have access to Cherry's article, but "soft nonlinearities"
usually refers not to clipping but to active device saturation.