Automated Phase Shift

Automated Phase Shifts

Objective

To ensure that the Raspberry Pi, DAC, Step Up Booster and PCB with Op-Amp and Phase Shifter can work together to accomplish a phase shift ranging from 0 to at least 180 degrees.

Proof of Concept

Using the Raspberry Pi a user will be able to input a voltage that will be the output of the DAC. The DAC output will then control what phase shift of the op-amp. The step up booster is also powered by the Raspberry Pi and gives the supply of the op-amp 15V. Once the PCB is powered and connected to the calibrated VNA and graph the S21 Phase. .

Pass criteria: Minimum Phase shift range of at least 0º to 180º or above 180º
Fail criteria: Phase shift range of anything not within 0º to 180º or above 180º

Methods

Need to ensure that the Raspberry Pi, DAC, Step Up Booster and PCB can perform a phase shift from 0 to at least 180 degrees in the 915 MHz ISM frequency band. Connect the Raspberry Pi 5V, ground, SDA, and SCL to the DAC, then connect the input of the PCB op-amp to an output terminal of the DAC. Connect the 5V and ground to the step up booster and connect PCB op-amp bias voltage to the output of the step up booster. Next, performing a 2 port calibration such that the calibration plane was established at CH0 of the VNA for a frequency range of 900 MHz to 950 MHz with 1 segment of 101 points. Connect the PCB RF input to CH0 of the VNA and the PCB RF output to CH1 of the VNA. We began this test by running the DAC code and inputting the voltages from 0 to 15V in steps of 0.1V and performed a frequency sweep plotting the S21 Phase. Once all the phase shifters were tested, we set our reference phase shifter to be the one with the greatest phase shift range.

Results

Our ideal phase shift for the phase shifter and op - amp test would be from 0º to 180º or higher than 180º when having a gain of 5V/V for the output of the op - amp. Once connecting the Raspberry Pi, DAC, step up booster, and PCB we were able to see the phase shift at each of the input voltages that we received from the user from the Raspberry Pi. These results match the datasheet for both of the LM358 Op - Amp and the JSPHS-1000+ Phase Shifter.

PCB 1