Is it possible to use a differential output/input to a mixer's IF port single ended?

[Hawaslsh]

Hello all,

I posted a question about the LTC5552 (datasheet) mixer and the use of a balun about a week ago, but I had a follow up question. I also posted this question to the Analog Device help forum a while back but never got an answer. According to the datasheet, the IF port of the mixer has an IF bandwidth of DC - 6 GHz, and the port is differential. Would it be possible to use the IF port single ended without using a balun? The datasheet has this to say about the IF port and using it single ended.

IF+, IF– (Pins 2, 3): Differential Terminals for the IF. These pins may be used for a differential IF or connected to an external balun if a single-ended IF port is needed. The IF port can be used from DC up to 6GHz depending on the external balun bandwidth. DC voltages at IF+ and IF– are 0V.

I couldn't find a balun that has a wide bandwidth that also reaches pretty low in frequency; ideally 10 KHz - 3 GHz in my case. I would presume when using the mixer as a downconverter, using the IF as an output, I could easily terminate one end of the differential output with a resistor and take the output from the other end?
However, if i wanted to use the mixer as an upconverter, using the IF as an input, could the same approach be taken? If it isn't possible to use the IF port single ended, it seems that no one could ever use the IF port to its fully potential bandwidth of DC- 6 GHz and would always be limited by whatever Balun they can find?

Thanks in advance,
Sami

 

[BigBoss]

Are you really interested in working with DC to 6GHz ?This is huge bandwidth as you imagine.
If you're just interested in some fraction of that bandwidth, you can find a balun which will serve you in this bandwidth. Otherwise. you can use Wideband Isolated Transformers but their bandwidth is even wider, Phase Balance is worse.
At worst case, you can use single output of the IC, I believe this will be a rational solution for this huge bandwith.

 

[FvM]

Simply consider that there's no simple solution for a 10kHz - 6 GHz balun. A transmission line transformer with large core can - in principle - achieve the bandwidth, but surely involves an impedance matching compromise in the high frequency range due to its dimensions. The "natural" backend for a DC capable mixer is a differential ADC, DAC or wide band amplifier.

Datasheet doesn't tell much about the IF port properties, it only states:

An external 1:1 balun is required for a 50Ω single-ended IF

I'd expect a performance degradation, if you interface the mixer with a single ended 25 ohm (or even 50 ohm) source/load. But how severe would have to be evaluated. Need to acquire IIP3 curves for single ended operation.

 

[vfone]

https://www.markimicrowave.com/Assets/datasheets/BAL-0006SMG.pdf?v=110220