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sunstar16 Post subject: unbanlance of ACPR Posted: Wed Nov 16, 2005
11:15 pm Lieutenant Joined: Tue May 24, 2005 2:37 am
Posts: 1 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. Top
vipness Post subject: Posted: Wed Nov 30, 2005 3:53 am This
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
cables. Top Guest Post subject: Posted: Thu Dec
01, 2005 11:30 pm VIP, 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. Just wondering.
Top IR Post subject: Posted: Sat Dec 03, 2005 4:33
am Site Admin Joined: Mon Jun 27, 2005 2:02 pm
Posts: 373 Location: Germany Hello 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.
Good Luck! _________________ Best regards, - IR
Posted 11/12/2012
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