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: unbanlance of ACPR Posted: Wed Nov 16, 2005
Joined: Tue May 24, 2005 2:37 am
When testing the ACPR of CDMA PA, the difference between
upper frequency and lower frequency was a little big. For example, the
amplitude of +750KHz was -46.6dBc, while that of -750KHz was -49.9dBc.
But normally, these two value were almost same. Could you tell me what
would cause this and how to avoid? Many thanks.
Post subject: Posted: Wed Nov 30, 2005 3:53 am
is a common problem when designing PAs for relatively wide band waveforms
(>1MHz BW). It's called a memory effect, and is basically a voltage
ripple on your power supply feed (drain for LDMOS). Can be remedied
with larger values of capacitors (10uF to 220uF) on supply feed, or
de-coupling network. Also, try minimizing length of all DC lines or
Post subject: Posted: Thu Dec
01, 2005 11:30 pm
Are you sure that this is called memory
effect? If I recall well this is just called signal envelope decoupling.
I tought memory effect involved instrinsinct semiconductor issues
and not only surrounding circuitry consideration.
Post subject: Posted: Sat Dec 03, 2005 4:33
Joined: Mon Jun 27, 2005 2:02 pm
VIP is right in he
post. It is a memory- effect related. Memory effect has to do with working
on a wideband frequency range under which the amplifier behaves differently.
The amplifier behaves somewhat as Filter - has different AM-AM &
AM-PM behavior over the entire band and this is shown as different linearity
(ACPR) performances. VIP is also right in his suggestion for remedy
to this problem. The bypassing network should contain several values
of capacitors and often ferrite beads and resistors - it is always useful
and helpful to consult the data sheet of the specigfic device.