RF receiver Input Matching

I am measuring the RF receiver without any input matching and see a very noisy downconverted signal instead of a single tone. Is the circuit oscillating? How do I determine whether the circuit is oscillating or not?

Thanks

the noise in output , maybe due many things
1) supply noise
2) digital noise coupling
3) no matching

try to match the input and measure , coz when the input is not matched , there is no max power tranfer between the source and ur LNA

and if there are any interface , try to match it , like the filters and the output or ur LNA , and from the filter to the MIXER

also chek the purity of ur LO , it can degrade the received signal

khouly

Usually if the front-end is not matched the gain is low and the possibility of oscillation is lower also. Try to disable the LNA Vcc and do the same test with higher input level to compensate for LNA isolation with Vcc OFF, and check what you get at the system output.
If the noise is still there the reason is not the LNA.

also u should tell , what kind of noise ?
is it noise , or it is a spurs ?
it is spurs , then it may be oscillation or feedthrough from LO

khouly

Hi Vfone,

Could you please tell more about the reason that you can tell LNA contributing noise by Vcc off and higher Vin test condition ?

What mode of operation for LNA by this way ? LNA is enabled while no Vcc bias ?

Thanks !

i think Vfone , mean when u off the VCC of the LNA , this will disable it , and increasing the input power to over come that u lost the gain of LNA

he told to disable LNA , to check if it oscillate or not

khouly

Today a lot of RF receivers use multiple states for LNA.
ON, OFF, or Short (bypass).
For OFF position they just do not supply the Vcc of the LNA, and the through insertion loss is based on the isolation of the LNA.
If disable the Vcc of the LNA for sure it will not oscillate :D