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Design >> RF Design >> problem with LO square and LO sinsoid
https://designers-guide.org/forum/YaBB.pl?num=1186781164

Message started by James Bond on Aug 10^th, 2007, 2:26pm

Title: problem with LO square and LO sinsoid
Post by James Bond on Aug 10^th, 2007, 2:26pm

Hi, all,

I met a strange problem. When I did the simulation for the passive mixer, I apply a LO square signal to the switches of the mixer, it works fine, two of the switches are in linear region and others are off. But when I apply a sinsoid signal , it didn't work, all the switches are off. Has anybody met this problem before? Any idea would be appreciated.

Thank you very much.
James

Title: Re: problem with LO square and LO sinsoid
Post by aaron_do on Aug 11^th, 2007, 8:33pm

Its probably a problem with your DC biasing. It should work with sine wave.

Title: Re: problem with LO square and LO sinsoid
Post by James Bond on Aug 12^th, 2007, 12:07am

Hi, aaron_do,

I have tried both way:

1. No bias for the passive mixer, I use ideal LO square, 600mVpp, it's working, but when I changed to LO sinusoid with the same amplitude , it didn't work.

2. If I have a 300mV bias to the gate of all the switches, applying a 300mVpp LO square, it's still working. but when I changed to LO sinusoid with the same amplitude, it didn't work.

It's quite wiried I think, is it possible that maybe some settings in the spectreRF or some properties of model will affect this ?

Title: Re: problem with LO square and LO sinsoid
Post by aaron_do on Aug 12^th, 2007, 4:30am

hmm...that's strange. What simulation are you running? I would check the DC bias points of all the nodes and also check the LO amplitude at the mixer gate to make sure there's actually an LO signal...

cheers,
Aaron

Title: Re: problem with LO square and LO sinsoid
Post by James Bond on Aug 12^th, 2007, 9:03am

HI,

Let's say we have a 300mV dc bias applied to all the gate of the switches, and sinusoid LO+ amplitude is 300mVpk to one of the pair, and LO- has 300mVpk to the other pair. Then the dc simulation is run.

I check the dc operating point, all the switches have the Vgs = 300mV, Vds = 0, Vth= 569mV, actuall, the amplitude of sinusoid didn't add to the gate voltage. The 'region' is 0, this is also very strange, at least it should be region 3(weak inversion) I think.

Title: Re: problem with LO square and LO sinsoid
Post by aaron_do on Aug 13^th, 2007, 1:38am

Hi James,

I don't really know what's wrong but i can tell you i've never had a problem simulating a passive mixer with sinusoid LO. I usually set the DC bias voltage to be around 450 - 500 mV where vth is around 480 mV.

Aaron