Re: LNA current output+Mixer current input.Need matching?Hel
1st,
you have to know, WHY you need a matching network. Why power match? For example, how much is the difference of injected power between reflection gamma = -3dB and -10dB? The answer is, the input power nearly doubles when reflection gamma improves from -3dB to -10dB. And if this is the S11 parameter of your LNA, S11 improves from -3dB to -10dB means that a 3dB improvement in power gain, if the LNA is still unilateral (i.e S12 is small enough).
Well, if 3dB is a enticement to you, than a amplifier with an S22 around -3dB deserves to match. Otherwise, if the power gain is large enough to meet the specification, there is no need to do this interface matching network. Though a matching network boosts gain, lower down noise, it degrades linearity.
And the other reason (Imortant) to apply a matching network to our system, is to assure that the SAW filter has power matched interface both at input and output interfaces. Why we have to ensure these interfaces to be power matched? Because we want SHARP EDGEs and FLAT IN-BAND ATTENUATION.
For a system without SAW filter, and the front-end power gain meets the specification, there's no need to pay more to make a matching network unless you have too much Money.