Reference Design and PCB mounting
Reference design files¶
A complete reference design including PCB layout and PCB design guidelines is available from LumenRadio to make integration easier. Please send your inquiry to LumenRadio for details.
The antenna connector of the module is of u.FL type. A coax cable with a characteristic impedance of 50 ohm shall be used to connect an antenna. The antenna shall have a characteristic impedance of 50 ohm at 2.45GHz.
Layout considerations for the main board¶
TimoTwo has been specifically designed in order to achieve good RF performance. In order to maintain this, there are some guidelines that we would like to stress:
The use of ground planes also on the main board cannot be emphasized enough. Good decoupling of any high speed digital circuitry is a must. Many embedded type microprocessors today have clock frequencies with clocks or overtones that reach well into the GHz range. It is perfectly possible for an embedded design to pass any EMC certification and still cause disturbances that will block the RF reception of the TimoTwo module. The sensitivity of the TimoTwo receiver is -96dBm therefore it is recommended to keep disturbances below -100dBm in the frequency range of operation.
A near field probe connected to a spectrum analyzer will show if there are any disturbances present on the 2.45 GHz band generated by the microprocessor or any other device that is placed on the main board. Pay special attention to readymade LAN-products "Server in a RJ connector". They pass EMC certifications, but some of them radiate badly on 2.45 GHz. If disturbances can be seen on a spectrum analyzer - then the TimoTwo module will have impaired reception.
TimoTwo has a supply voltage decoupling on the circuit board. The supply voltage still needs to be adequately filtered. If any disturbance or intermittent communication failures occur, as one of the trouble shooting steps - check the supply voltage for drop-outs, switch supply ripple etc.
- The TOP layer inside the footprint must be free from copper. There is a ground plane on TimoTwo, but there are also supply lines. It is an unnecessary risk to rely on solder mask lacquer for isolation.
- An area around the board edge must be kept clear from copper on all layers as depicted in the picture below.
Minimum dimensions for ground plane clearance for optimum performance are shown below: