Radiometrix Ltd, BIM2/3G Data Sheet

page 2

Functional overview

The transmit section of the BiM2/3G consists of a frequency modulated crystal locked PLL feeding a buffer

amplifier and RF filter. A Tx select line controls operation. The transmitter achieves full RF output typically

within 1ms of this line being pulled low. Modulation is applied at the TXD input and may be either a serial digital

stream toggling between 0V and 5V (digital drive) or a high level analogue waveform with the same peak limits

(linear drive). Modulation shaping is performed internally by a 2nd order lowpass filter, which minimises spectral

spreading. The RF output is filtered to ensure compliance with the appropriate regulations and fed via a Tx/Rx

changeover switch to the antenna pin.

The receive section is a single conversion FM superhet with an IF of 10.7MHz. A SAW bandpass filter in the

receiver front-end provides image rejection and suppression of other unwanted out-of-band signals. Like the

transmitter, the receiver is controlled by its own active low RX select line. A post-detection lowpass filter

establishes the signal bandwidth and ensures clean operation of the subsequent adaptive data slicer. The slicer

is optimised for balanced data such as bi-phase code. A received signal strength (RSSI) output with 60dB of

range is provided. A version of BiM2/3G featuring a fast acting Carrier Detect (CD) output on the same RSSI

pin is also available. The CD output will indicate the presence of any RF signals on the carrier frequency.

18

17

16

15

14

13

12

11

10

0V

Vcc

RX SELECT

TXD

TX SELECT

AF

RXD

RSSI/CD

0V

1

2

3

4

5

6

7

8

9

RF GND

Antenna

RF GND

0V

No pin

33 mm

30.48 mm

23 mm

5 mm

side view (through can)

top view (without can)

side view (with can)

recommended PCB hole size: 1.2 mm

module footprint size: 25 x 32 mm

pin pitch: 2.54 mm (0.1")

pins 4, 5, 6, 7

are not fitted

& 8

Fig. 2: Physical dimensions

Pin description

RF GND

pins 1 & 3

RF ground pins, internally connected to the module screen and to pins 9, 10 & 18 (0V). These pins should be

connected directly to the RF return path (e.g. coax braid, main PCB ground plane etc).

Antenna

pin 2

50

Ω RF connection to the antenna, DC-isolated. See pages 7 & 8 for details of suitable antennas and feeds.

0V (GND)

pins 9, 10 & 18

Supply ground connection and screen.

RSSI /CD

pin 11

RSSI variant: Received Signal Strength Indicator with 60dB range, operational when Rx is enabled. Output

voltage nominally 0.50Vdc (no signal), 1.0Vdc (maximum strength). See page.6 for typical characteristics.

Carrier Detect variant: When the receiver is enabled, a low indicates a signal above the detection threshold is

being received. The output is high impedance and should only be used to drive a CMOS logic input.