Transmitter Output: What is this capacitor used for?

[VAURIEN]

what is tranmitter

Hi,

I'm currently trying to understand the schematics of a 433 MHz Transceiver. I've got a differential transmitter output as to be seen in the attached picture. L1/L2 are there to couple in a DC voltage, C4/C5 prevent any DC to enter the following stage. C1/C2 and L3 are used for impedance matching.

Though: I'm not sure for what reason C3 is there. It has about no influence on impedance matching (as XC3 ≈ -0.17Ω, XL3 ≈ 272Ω). So the only reason for C3 can be blocking DC voltage. But why do we need to block DC voltage here? Or am I completely wrong?


Can someone explain to me what's the reason for C3 here?



Thanks in advance for any help !!

 

[biff44]

what is a capacitor used for

Just a guess: oscillation suppression.

 

[kspalla]

what are capacitors used in making transmitter

It could be matching for input side.
Differential circuits at the receive end must have proper termination.

 

[vfone]

How can be the matching of the receiver input when this is a transmitter output !?

What is interesting is the 10.7MHz resonant frequency of L3 and C3, which is a common IF frequency in FM radios.

 

[kspalla]

Hi VAURIEN, Can you tell us if this chip is transmitter alone or it has the receive to this pins?
From where this 10.7MHz or IF is coming while VAURIEN is talking about 433 MHz Transceiver.

 

[VAURIEN]

Hi,
no, this pins are purely transmitter output - there are other pins for receiver input.

The 10.7 MHz must be a coincidence, behind the C4/C5 capacitors there's a balun to make the signal single ended, followed by a circulator to transmit / receive with the same antenna.

Preventing oscillation might be an idea, not sure about that though.