MSP430 CCRF

[bird]

Hello,

I just purchased this board. I want to make connection with an ez430 chronos. First I want to use SmartRF to control the MSP430 CCRF....

What about R13, C31 an C32? Why are they not placed? And what are the values of the C's? Can the board be used without those components, with low range?

Thanks in advance,

Bert

[LubOlimex]

Hey Bert,

MSP430-CCRF is based on a Texas Instruments design. The capacitors C31 and C32 weren't placed in the original design so we didn't mount them also. It is common practice in electronics to have pads for different capacitors and/or resistors in case you want to use the board in a way much different than the initially intended.

C31 and C32 are signal filter and have to be mounted/dismounted together.

R13 should be mounted it has 0R value though.

Best regards,
Lub/OLIMEX

[pepsi]

Hi Bert and Lub/OLIMEX

As described in DN024 (http://www.ti.com/lit/an/swra227e/swra227e.pdf), these components are meant to be used to match the impedance of the antenna to the transceiver chip. Ideally, the impedance seen towards the antenna is the same (or complex conjugate) as the impedance seen towards the cc430 for maximal power transfer. According to the TI reference design, the point at C30 on the MSP430-CCRF should have 50 Ohms.

I did some measurements to verify that. If the impedances are matched, there should be very little energy reflected back. In my setup, the MSP430-CCRF board was attached to another PCB. I measured a return loss of -2 dB towards the PCB antenna and a return loss of -6.76 dB towards the receiver. A good return loss value would be lower than -10 dB. It seems as if there is quite some room of improvement the MSP430-CCRF board with respect to the RF circuit.

Measurements on the TI reference module (EM430F5137RF900) showed a return loss towards the receiver of -9.49 dB. I don't have measurements for the antenna as this board has a SMA connector for an external antenna.

I guess the problem with the MSP430-CCRF board is the fact that it was designed according to the TI reference, but with a different size of components (603 instead of 402). This results in different characteristics for the RF part, because of different parasitics and trace dimensions.

I have no clue on how to improve return loss towards the receiver with 603 components, but matching the antenna to 50 Ohms using the non-populated pi network (R13, C31 an C32) might be a good start to improve the RF performance.

Cheers
Roman