0.1 Design of an in-vivo radiation measurement scheme using a  (Page 5/7)

Fig. 12(i)Fig. 12(ii)

The output analog signal of the radiation sensor (within the specified audio bandwidth) is connected directly to the transmitter’s DATA line. The transmitter input is high impedance (500kΩ) and can be directly driven by the sensor output signal. This analog source provides no more than 5VP-P maximum waveform (within the input level) and is AC-coupled into the DATA line. The size of the coupling capacitor is selected to be large enough to ensure the passage of our signal frequencies of interest. Since the modulation voltage applied to the DATA line determines the carrier deviation, distortion can occur if the DATA line is over-driven. So, the actual level of the input waveform is adjusted to achieve optimum in-circuit results.

The receiver, RXM-916-ES, is capable of receiving a signal as low as -97dBm (typical). The signal is filtered at its front end by a SAW band-pass filter. The filtered signal is then amplified and down converted to the IF by mixing it with a LO frequency generated by a PLL-locked VCO. The IF is then amplified and filtered. Finally, a PLL demodulator is used for recovering the baseband analog signal from the carrier. The ES receiver features an on-board data slicer for recovery of data transmission. Its output is internally derived from the filtered analog baseband, which is squared and made externally available on the DATA line. The data slicer is capable of recreating squared waveforms from 100Hz to 28 kHz, giving a data rate bandwidth of 200bps to 56kbps.

1/4–wave Monopole Chip antennas based on advanced Low Temperature Co-fired Ceramic (LTCC) technology are used to transmit and receive the modulated data on both the sides of transmitter and receiver. These antennas are ideal with excellent electrical specifications delivering 50Ωcharacteristic impedance.

As explained in the previous section, the voltage signals with the frequencies 50Hz, 80Hz and 100Hz and peak-to-peak voltage 5V are given as input to the sensor. The output signals (inverted) from the sensor are connected to the DATA line of the RF transmitter. At the transmitter side, the modulated analog data is transmitted using a chip antenna. The data is received at another chip antenna on the receiver side which is then demodulated and made available at the DATA line of the RF receiver.

7.1 LabVIEW Setup:

The National Instruments LabVIEW graphical development environment helps in creating flexible and scalable design, control, and test applications. The LabVIEW VI is designed to use a National Instruments DAQ (Data Acquisition) card with the model NI-6251E and the screw terminal connector blocks with the model CB-68LP. The first part of setting up the hardware is to wire up the connector block for two analog inputs.

The output data of RF receiver is connected the analog input channel #2 (AI-2). The receiver GND pin is connected to the analog input gnd (AI-GND). User inputs can be taken to set the sampling rate and sample display rate. The sampling rate is set at the maximum value of 24,000 samples/sec and the display rate is set at 50 samples/sec. We can start the LabVIEW‘Receiver_data.vi’by clicking on the Run button on the toolbar. Data that is being read from the analog input channel will appear on a graph.