Final+Results

Final Results

The s-parameters of the final circuit were simulated. The gain, output reflection coefficient, and input reflection coefficient are shown as Figure 4.6.1, 4.6.2, and 4.6.3 (respectively). Figure 4.6.1 – System Gain Figure 4.6.2 – System Output Reflection Coefficient Figure 4.6.3 – System Input Reflection Coefficient The final gain of the circuit was measured by using a system input from a function generator, and the system output was measured using the oscilloscope. A 10 mVpp 20.1 MHz sine wave was output from the function generator. With the oscilloscope input set at 50 Ohms, the measured peak-to-peak amplitude was 1.82 V with no visible distortion. Thus, the output gain can easily be calculated. However, one must also take into account the fact that a 12 dB attenuator was present on the system output at the time. Therefore, the actual output is given by Equation 4.6.2. The minimum discernible signal was tested by first passing a 20.1 MHz signal from a function generator (and attenuated through the channel created by two antenna) to a spectrum analyzer such that the signal level was just barely above the noise floor. According to the spectrum analyzer, the signal input was approximately -97 dBm, as shown in Figure 4.6.4. Figure 4.6.4 – MDS Input Test Signal Next, this minimum signal was passed through the receiver itself. The output of this was observed on the spectrum analyzer, and is shown in Figure 4.6.5. Figure 4.6.5 – Signal Level At Receiver Output Next, the signal was attenuated until it reached the noise floor in the passband of the receiver. This is shown in Figure 4.6.6. Figure 4.6.6 – Receiver Output After Attenuation At the minimum signal level that the function generator could generate, it still was not enough to fully attenuate the signal to the noise floor in the passband of the receiver. The receiver was nonetheless removed from the path, and the antenna output was plugged directly into the spectrum analyzer. The output is shown in Figure 4.6.7. Figure 4.6.7 – Raw Signal Output Thus, the function generator cannot even produce a signal that can bring the receiver output to its noise floor. But, as best as the spectrum analyzer can measure, the minimum discernable signal that the function generator can detect above the noise floor is -101 dBm. However, since the function generator could not provide enough signal attenuation to fully bring the received signal output to the receiver noise floor, it stands to reason that the noise floor is even further below this level, and may indeed be the projected -106 dBm.

Next, the spurious free dynamic range was measured. This was accomplished by first hooking up the receiver output to the spectrum analyzer, and forcing the function generator to output two sine waves at differing frequencies (20.1 MHz and 20.2 MHz) through the same channel (accomplished using the ‘add external input’ function on the function generator). The system output is shown in Figure 4.6.8. The amplitude of both sine waves was increased until the first spur due to intermodulation distortion could be seen. <span style="font-family: 'Times New Roman','serif'; font-size: 16px;">Figure 4.6.8 – IMD Spur for SFDR Test <span style="font-family: 'Times New Roman','serif'; font-size: 16px;">Next, the signal amplitude was decreased until this spur disappeared. The result is shown in Figure 4.6.9. <span style="font-family: 'Times New Roman','serif'; font-size: 16px;">Figure 4.6.9 – Amplitude Reduction to Eliminate Spur <span style="font-family: 'Times New Roman','serif'; font-size: 16px;">To determine the dynamic range, the signal level difference between the highest receiver signal and the noise floor of the receiver (stopband) at this amplitude was observed (delta marker in spectrum analyzer). This is shown in Figure 4.6.10. <span style="font-family: 'Times New Roman','serif'; font-size: 16px;">Figure 4.6.10 – Determination of SFDR <span style="font-family: 'Times New Roman','serif'; font-size: 16px;">Thus, the observed SFDR is approximately 75 dBm.