I would like to introduce here a method,
which can be used for example in a phase difference measuring device.
1. An IQ signal (I2, Q2) is generated and output by use of a DA converter (reference signal).
2. A signal is read with an AD converter.
3. From this signal, a pseudo IQ signal (I1, Q1) is formed.
(Pseudo IQ means that only for a certain frequency a phase shift of 90 degrees is fulfilled.)
4. The phase difference between the two IQ vectors is calculated
using scalar product and simple analytical geometry.
a component of the referenze signal is output at DA0 of the Propeller Activity Board and connected with AD0.
It would also be conceivable to switch an electrical two- or four-pole between DA0 and AD0.
After a measuring period of pi / 2, the calculated phase difference is output via serial interface to a terminal.
a jitter in the measured value is to be determined. My guess is that the noise of the DA converter has a big impact.
Per software (see sourcecode) can the output
of the reference signal (Q2) "switched" directly to the input. The phase difference. is then like
expects pi / 2.