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jom Post subject: Need suggestion of suitable amplifier Posted:
Wed Aug 22, 2007 5:14 pm Captain Joined: Fri Jan
26, 2007 2:40 am Posts: 14 Hello I need to use an amplifier
that can handle the following: Output: 12 dBm Gain: 20 to
25 dB Frequency Range: 1 MHz to 30 MHz Harmonic distortion: >
-50 dBc It's the last spec I'm having trouble with. We've looked
at Minicircuit amps which give high compression points (20 dBm or so)
but the harmonic distortion is -30 dBc which is not good enough. I also
noticed these Mini amps do quite a bit better when you set the DC current
higher but that is NOT what they are specified at. Any alternative
ideas? Thanks jom Top jom Post
subject: Posted: Wed Aug 22, 2007 5:16 pm Captain
Joined: Fri Jan 26, 2007 2:40 am Posts: 14 Forgot one more
thing: The power supply can be +8 or +15 V. Thanks jom
Top IR Post subject: Posted: Sat Aug 25, 2007 3:41
pm Site Admin Joined: Mon Jun 27, 2005 2:02 pm
Posts: 373 Location: Germany Hi Jom, Here is a gain block
- SBF-5089 from Sirenza Microdevices: https://www.sirenza.com/documents/produc
... SBF-5089(Z)_Green_Datasheet.pdf It will meet all the requirements
you listed. Good luck!! - IR Top
jom Post subject: Posted: Sun Aug 26, 2007 11:19 pm Captain
Joined: Fri Jan 26, 2007 2:40 am Posts: 14 Thanks for
that! This amp seems very similar to the Mini-circuits amp I'm
using. Do you have any experience with it? It seems the Mini
amp is a bit current starved for some reason, especially at low frequencies.
I'm wondering if this might be the case with this Sirenza amp. Neither
amp gives any kind of harmonic distortion data. On my Mini-circuits
amp I adjusted the bias voltage (thinking it was voltage limited) and
noticed a marked improvement in the harmonic distortion. However, as
I had raised the voltage the current went up also so I adjusted the
bias resistor (to keep the same current) while raising the voltage and
the harmonic distortion got bad again..this all with just a 10 dBm output
signal (with -15 dBm in). So I'm thinking it's a bit current starved.
However, raising the current in the device to above it's rated value
isn't a very good idea. Any ideas? Thanks again!
jom Top IR Post subject: Posted: Mon Aug
27, 2007 6:00 am Site Admin Joined: Mon Jun 27, 2005
2:02 pm Posts: 373 Location: Germany I have no experience
with this amplifier. Usually manufacturers proivde IP3 and IP2 parameters
and for more information you have to contact them. To see the real
non-linear behavior of the active device you need a non-linear model
(Like SPICE model). In general, an amplifier with better linearity
will give you better harmonic distortion supression. Top
Tony Kurlovich Post subject: Posted: Tue Aug 28, 2007 4:08
pm Captain Joined: Thu Oct 19, 2006 6:02 pm Posts:
7 Given a flat amplifier response the H3 will be lower than the
IM3 by 9.54db (20log3). This is because the coefficient for the third
order component is common to both. Given a flat or decreasing
gain with frequency, IM3-9.54db is a reasonable upper bound for H3.
When doing a 2 tone test there will be 4 spurs at around 3 times
the frequency. The larger ones are not 3A or 3B. The are 2A+B AND 2B+A.
The 3A and 3B components are the ones that are down by 9.5db.
Top jom Post subject: Posted: Fri Sep 07, 2007 5:12
pm Captain Joined: Fri Jan 26, 2007 2:40 am Posts:
14 After looking around a bit this seems to be a difficult problem
according to several vendors such as RFMD etc. Let me restate the problem.
I need a +10 dBm to +12 dBm output with Harmonic Distortion less than
-50dBc. The supply voltage can be a bit higher than what I said before
according to our customer 15V maybe. Also: Gain: 20 to 25 dB
Frequency Range: 1 MHz to 30 MHz After talking with apps
engineer at several places it seems this kind of low HD spec is a long-sought
after. Anyone know the basics of what is REALISTIC when it comes to
harmonic distortion in this range? Thanks jom
Top IR Post subject: Posted: Sat Sep 08, 2007 5:11
pm Site Admin Joined: Mon Jun 27, 2005 2:02 pm
Posts: 373 Location: Germany Hi jom, My suggestion is
that if it hard for you to find such an amplifier, and if it is possible
from your system point of view, then design a notch filter for the 3rd
harmonics. Should be a notch made of single L and C which will short
the 3rd harmonic frequency to GND. Thanks to Tony Kurlovich
for his post. Top jom Post subject: Posted: Mon
Sep 10, 2007 1:44 am Captain Joined: Fri Jan 26,
2007 2:40 am Posts: 14 Thanks for that.. However, it
seems I wasn't clear. The problem here is that this is a wide bandwidth
problem. Meaning the output can be anywhere from 1.5 MHz to 30 MHz so
a filter really can't be used, at least nothing below 30 MHz anyways.
Also, another thing is that it's not only the 3rd HD...in fact
the 2nd HD seems to be more of a problem. A "balanced" approach could
solve this but so far I've had trouble getting a good 180 degree shift
for that. And, of course, this does nothing for the 3rd HD.
jom Top Peter Raynald Post subject: Posted: Wed
Oct 03, 2007 12:35 pm Captain Joined: Tue Sep 07,
2004 3:09 pm Posts: 11 Would feedback be an option? I
think this is a linearisation technique that could be quite suitable
for your frequency range.
Posted 11/12/2012
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