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gui076 Post subject: Distribution of VCO Posted: Mon Jun 16, 2008
4:40 am Captain Joined: Mon May 05, 2008 9:56 am Posts:
15 Location: France Hello, i'm implementing a synthesizer
with one or more VCO. I will put some switch in order to choose
between the VCOs and after i would like to provide VCO's signal to two
Mixers. I have seen some application with dual VCO buffer, is
there other method ? Thanks Guillaume Top
nubbage Post subject: Posted: Wed Jun 18, 2008 3:33 am
General Joined: Fri Feb 17, 2006 12:07 pm Posts:
218 Location: London UK Hi Guillaume I have to split the
VCO output of my synthesizer into a -10dBm signal for the pre-scaler
and a direct signal at 0dBm into the VCO buffer followed by a mixer.
I just use a 10dB coaxial directional coupler on the VCO output.
If the buffer isolation into the mixer is inadequate, I also purchased
a coaxial isolator. The VCO runs at 1.3GHz. I only have the one
VCO running. If I were to design for a second one to cover a wider range,
I would use a coaxial transfer latching relay. This would ensure the
idle VCO saw a matched load when de-selected. Top
gui076 Post subject: Posted: Wed Jun 18, 2008 4:31 am
Captain Joined: Mon May 05, 2008 9:56 am Posts: 15
Location: France Hi nubbage, For my application it's to
drive two mixers and they have 0 dBm LO input, so i thought a buffer
will level the output to 0 dBm. I have a wideband VCO 950-2050 and
isolators wille be too narrow i think. For the switch i have
seen SP2T Absorbtive : https://www.macom.com/DataSheets/SW65-0313.pdf
I didn't know "coaxial transfer latching relay". Thank
you for your help, i'm student in RF so i'm discovering a lot of thing
Guillaume Top FSomma Post subject: Posted:
Wed Jun 18, 2008 4:54 pm Hi Guillaume I think you can use
the Tyco switch if you turn off the idle VCO with the same switch control
signals .. In fact, I think it could be a good design practice to turn
off the idle VCOs to ensure that you don´t have that tones around your
circuit while the other VCO is active. If your idea is to feed
the dwn conv mixer and the up conv mixer with the same LO, you can use
an splitter to feed them. If the isolation is critical (check the isolation
balance of the RF-LO of both mixers and the splitter S32), you can think
on changing the selected switch by an other one with no internal driver,
and to boost up the LO for the mixers, you can use independent drivers
on each output of the splitter to take advantage of their reverse isolation.
Top gui076 Post subject: Posted: Wed Jun 18, 2008
5:22 pm Captain Joined: Mon May 05, 2008 9:56 am Posts:
15 Location: France Hi, Yes the goal is to feed the up
and down mixers. So if i have well understood i should try this
config : VCO1 and VCO2 on SP2T followed by a splitter and one
buffer on each channel. Else there is a double VCO buffer from
Maxim : https://www.maxim-ic.com/quick_view2.cfm/qv_pk/2038/t/al
Thank you Guillaume Top nubbage
Post subject: Posted: Mon Jun 23, 2008 6:54 am General
Joined: Fri Feb 17, 2006 12:07 pm Posts: 218 Location:
London UK Hi Guillaume A latching coax relay is one that is
magnetically biassed so when an impulse is given to the coil it switches
over to the other state. Removing the coil drive leaves it in that state
until another pulse is received. This avoids the need to drive current
continuously into the coil for either state of the relay. I think mine
is from MAComm/Tyco. The isolation of a transfer switch, a relay that
transfers the unwanted signal to a load and the wanted signal to the
output port, is typically greater than 60dB, so leakage should not be
a problem. I hope not to use the isolator I purchased. It was just
for insurance "in case". The bandwidth is 20% of nominal centre. I think
it was from Anzac. I have some doubts about the wisdom of switching
off the unwanted VCO, particularly if low phase noise and rapid switching
time are important. Top FSomma Post subject:
Posted: Wed Jun 25, 2008 3:44 pm Hi Guillaume, Yes, the
"VCO1 and VCO2 on SP2T followed by a splitter and one buffer on each
channel" is one option. But if you don´t need that much isolation,
you can still think on the "VCO1 and VCO2 on SP2T followed by the buffer
you where thinking on the first place and a splitter to OL-feed the
mixers". Regarding to switching off the idle VCO, yes, nubbage
is right, you have to analyze your phase noise and rapid switching time
requirements. I think I assumed too quickly that your application was
a channel scanner (am I right?) where fast VCO switching is not that
important... i mean, you can scarify that response time when you switch
from band to band and save $$ to your design, coax relay are very expensive,
Radiall has some SMD low power coax relays that you might like to take
a view if you find it necessary. Take care
Posted 11/12/2012
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