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How can I match 100K om to 12K om - RF Cafe Forums
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cpeter
Post subject: How can I match 100K om to 12K om
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postPosted: Wed Mar 09, 2005 11:32 pm
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Joined: Wed Mar 09, 2005 11:20 pm
Posts: 2
I am doing a design:
AD9854 -> differential & quadrature signal -> 80MHz filter &
match network? -> AD8346
And:
output impedance of AD9854:
100k om
input impedance of AD8346: 12k om
how can I design
the filter & match circuit?
Thanks.
Peter
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Guest
Post subject: Impedance matching?
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postPosted: Sun Mar 13, 2005 10:18 pm
Peter,
Your question
leaves out some important information - such as the frequency range
involved.
The impedances you cite are only accurate at very low
frequencies. There is significant reactance present at any reasonable
RF frequency. (There's both bond wire inductance and bonding pad capacitance
to ground).
The implication is that you probably don't want to
match 100k to 12k, since you really won't have it anyway! Digital-to-Analog
converters are often driven into the summing junction of an operational
amplifier - which is a "virtual ground". From the classical RF viewpoint,
that's weird - but the DAC output is often essentially a current, which
must be converted to a voltage.
Check out Analog Devices' application
notes on the AD9854 - I'm sure that they don't show the kind of impedance-matching
network you're asking for.
Good Luck!
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cpeter
Post subject: Thanks.
Unread postPosted: Wed Mar 16,
2005 1:47 am
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Lieutenant
Joined: Wed Mar 09, 2005
11:20 pm
Posts: 2
You answer is very helpful, thanks a lot!
:D
Posted
11/12/2012
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