I've Got A Design Problem for You

[Ken Smith]

Here's a request from a client that I'm not so sure will work...

Signals available (at PECL levels):

1056 MHz, quadrature signals available, 0° and 90°

132 MHz, quadrature signals available, 0° and 90°

(Both from synchronously clocked counters... same clock.)

Client want me to design an Image-Reject Mixer that will produce as
output at either 1188 MHz or 924 MHz, with the undesired sideband at
least 25dB down.

Do you have other phases?

The normal "trig. law" image rejection mixer could be done with XOR
functions but the 132MHz's 3rd harmonic will be trouble. With some other
phases, the spurs can be reduced.

 

[Jim Thompson]

Do you have other phases?

The normal "trig. law" image rejection mixer could be done with XOR
functions but the 132MHz's 3rd harmonic will be trouble. With some other
phases, the spurs can be reduced.

--

Aha! A true RF guy. What are your phase recommendations?

...Jim Thompson

 

[Lasse Langwadt Christensen]

I read in sci.electronics.design that Lasse Langwadt Christensen



No, the task was to generate 1056 + 132 or 1056 - 132, without more than
a sniff of the other frequency.

1056 + 132 = 1188
1056 - 132 = 924

so ...

-Lasse

 

[Tam/WB2TT]

Jim,

You hit the nail on the head. I simulated the mixer in SWCadiii, and the
good news is that the unwanted (lower) sideband was about 25 db down *before
filtering*. The bad news is that the A -3B term was only about 11 db down.
Numbers are from FFT. Rather than design a microwave XOR, my frequencies
were 250 KHz and 25 KHz,

Tam