Antenna properties associated with CY8C4247FNI-BL493

[Anonymous]

We are prototyping a device compose of the CY8C4247FNI-BL493 chip, two clocks (24MHz and 32KHz), a digital gyro, and antenna chip (Johansson Technology: 2450AT18B100E). We have learned (reading about the module CYBLE-022001-00) that the trace connecting antenna pin (H7) on the CY8C4247FNI-BL493 chip and the chip antenna should have a specific shape (see attached pic), and impedance (50 Ohm) set by a couple of capacitors and inductors. Also, the 24 MHz clock looks key for a correct load capacitance. But before to move deep in the combination of all these small and critical details associated with the antenna, I would like to ask a basic question associated with the impedance between the pin antenna (H7) and ground on the board we are prototyping. Probing our prototype between the points mentioned above, we got a value ~2 Ohm after mount the CY8C4247FNI-BL493 chip. I understand 2 Ohm doesn't mean a short but still, it looks weird or not? On the other hand, when I probed same points in the bare board it looks open so the board itself is not short.

Thanks, 
Marcelo.

[GuhapriyanT_31 · Accepted solution]

Hello Marcello,

   

The resistance measured between the ANT pin and Ground is low because of an inductor connected from signal to ground as part of the built in BALUN inside the chip. Please note that, this will not result in a short at RF frequencies.

   

For CYBLE-022001-00), the two components next to the ANT pin are used for matching the ANT pin of PRoC BLE to 50 ohms. The other two components are used for matching the chip Antenna's impedance to 50 ohms.  For 2450AT18B100E, we took a deviation from the antenna datasheet because of space constraints and so we had to modify the matching network accordingly. But, you can choose to follow layout and matching recommendations the Antenna's datasheet also, if you have space for it in your board.

   

Thanks,

   

Guha