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impedance matching for the mixer output buffer

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surianova

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I have a question regarding the mixer. Currently, i design a mixer and going to tape out soon. My mixer is operated at 2.4 GHz and output frequency is 3 MHz and i need connect the mixer to a buffer for measurement purpose. Do i need a 50 ohm impedance matching for the output buffer? Because as i know, for low frequency (3MHz), it is not require impedance matching at the output. I thinking of should i have this output 50 ohm for the buffer. Appreciate if can help me to clear this doubt. Thank you very much.
 

Generally Mixer output impedances are pretty high.You have used probably Gilbert Cell haven't you ??
You should connect a buffer amplifier/drive with high input impedance and low output impedance.At 3MHz, this can be an OPAMP.
 

BigBoss said:
Generally Mixer output impedances are pretty high.You have used probably Gilbert Cell haven't you ??
You should connect a buffer amplifier/drive with high input impedance and low output impedance.At 3MHz, this can be an OPAMP.
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if the buffer is going to connect to VNA or spectrum analyzer that has internal impedance of 50 ohm, should i match the output impedance of the buffer with 50 ohm to the spectrum analyzer with operating frequency of 3 MHz? Thanks
 

Hello
Yes, for measurements you should match mixer output impedance to 50 ohm either using passive components (which is rather unpractical at 3 MHz) or more convenient - using buffer circuit.
 

Ideally if the mixer output is matched to 50 ohms, is to use a diplexer at the output of the mixer, providing in this way a broadband good return loss.

Can use this small freeware program to calculate the components:

**broken link removed**
 
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