1) First time, we planned to use a analog mixer for phase detect.
but the different of two signal amplitude affect the output value.
mixer phase=sin(wt+a)*sin(wt) then filter=> phase=sin(a)
if mixer phase=g1*sin(wt+a)*g2*sin(wt) filter=> phase=g1*g2*sin(a);
So if you compare the phase of two signal, at first you have to measure
signal's amplitude , or useing a log amplifier to make a stable amplitude
it eliminate gain affection by phase detecter. like as Analog device inc's AD8302 phase function.
2) the other method, we selected a I/Q detecter for phase measure.
RF 1-30Mhz downconvert 10Khz IF signal, like as Radio receiver, I/Q detecter
IF signal. I/Q detecter need a local sin(wt)/cos(wt).
first channel IF signal g(sin(wt+a))
I/Q Detecter i=g(sin(wt+a)*sin(wt) filter=>i1=g*sin(a)
q=g(sin(wt+a)*cos(wt) filter=>q1=g*cos(a)
=>a=arctan(i1/q1)
second channel IF signal g(sin(wt+b))
I/Q Detecter i=g(sin(wt+b)*sin(wt) filter=>i2=g*sin(b)
q=g(sin(wt+b)*cos(wt) filter=>q2=g*cos(b)
=>b=arctan(i2/q2)
two channel phase measure = a-b = arctan(i1/q1)-arctan(i2/q2);
I/Q detecter isnot need a stable amplitude. Of course, you also can ADC IF signal
and DSP I/Q process.
But all of above method, several mixer are used in system. Mixer have many issues,
In RF 1--30Mhz bandwidth, Mixer have different gain, you have to calibrate the mixer's
error.
if ADC IF siganl for I/Q detecter, why don't we use a high ADC convert for RF, like as
software radio technology, directly ADC RF signal(1Mhz--30Mhz) with equivalent sampling.
The Method of RF ADC convert, DSP process ,this method eliminate the most error in traditional method.
that's my opinion, sorry for my poor english, hope your could undstand my explanation.
my project is design a vecter network analyzer in RF.
my private email:
ovenqin@263.net
welcome to detail discussion.