CC1201: cc1201

Joseph Sasson

Prodigy 40 points

Part Number: CC1201

Dear

In the specs. there is a capacitor of 0.9p connecting to the antenna.

The admitance of this capacitor at 400MHz is more than 400 ohm.

This seems to be very low value pf capacitor.

What is the reason to this value?

over 6 years ago

0 TER over 6 years ago

TI__Guru**** 317180 points

Could you please post a link to the design you are looking at?

It sounds like an antenna match cap but need to know exactly which design you are referring to to say for sure.

0 Joseph Sasson over 6 years ago in reply to TER

Prodigy 40 points

The reference dsighn is SWRR122

0 Keith Barkley over 6 years ago

Guru 42085 points

I love being pedantic:
You mean that the *impedance* of the capacitor is more than 400 ohm. The *admittance* is 2.3mS.

It is for matching and probably harmonic suppression.

0 TER over 6 years ago in reply to Keith Barkley

TI__Guru**** 317180 points

Yes, ANT2 (0.9 pF) is for antenna tuning.

On your board the matching most likely has to be different since the matching is dependent on the ground plane, if any objects are close to the antena and the casing used.

0 Joseph Sasson over 6 years ago in reply to TER

Prodigy 40 points

If the output of the amplifier is 50 ohm, and the antenna impedance is 50 ohm, why do i need a matching component?

0 TER over 6 years ago in reply to Joseph Sasson

TI__Guru**** 317180 points

I highly doubt that the antenna is 50 ohm, ref #4 in www.ti.com/.../swra496a.pdf as an example. The antenna impedance on the EVM is different due to the board size but these antennas tend to have an impedance in the lower part of the smith chart and hence need antenna matching.

0 Keith Barkley over 6 years ago in reply to Joseph Sasson

Guru 42085 points

What makes you think the PA is 50 ohms? :

0 TER over 6 years ago in reply to Keith Barkley

TI__Guru**** 317180 points

I assumed he meant the output of the matching network (R181)

0 Joseph Sasson over 6 years ago in reply to TER

Prodigy 40 points

In the sceam TI supplied there are 2 option of connecting the output.

One option is to 50 ohm RF connector and this one is without the matching for the antenna.

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CC1201: cc1201