# 400Mhz Phase Detector circuit

Discussion in 'Wireless & RF Design' started by Cery, Nov 27, 2014.

1. ### Cery Thread Starter New Member

Nov 27, 2014
7
0
Hi,
I don't know whether this is the right Forum tell me if not.
I'm trying to develop a Phase Detector circuit.
In theory it's pretty simple:
I've got two 400Mhz sine wave signals with different phase offsets.
Then i convert them to a square wave signal by using a simple Op-Amp or Comparator.
Problem 1: I wonder wich Op-Amp I should use for a 400Mhz signal. Or do i need to use some kind of comparator for Frequencies that big?

Problem 2: How do i then perform some kind of XOR Logic?
I thought about adding one Signal in reverse to the other and then cut of any negative current with a diode...

I'm pretty new to this topic, feel free to post any links or Websites which could help.
Greetings,
Cery

2. ### Papabravo Expert

Feb 24, 2006
10,340
1,850
What voltage level and source impedance are we talking about?

3. ### Cery Thread Starter New Member

Nov 27, 2014
7
0
~50 ohm Impedance
at 1.5V.
-hopefully...

Thank you,
Cery

4. ### Papabravo Expert

Feb 24, 2006
10,340
1,850
That is a reasonable signal level to work with. I don't think you will find standard TTL or CMOS logic familes able to work at those speeds. You might have a shot with PECL, or Positive Emitter Coupled Logic for the XOR function. I haven't found any discrete opamps or comparators that will work at those speeds, but that doesn't mean they don't exist. Since your signal inputs are sine waves, why do you think an XOR phase detector will be effective even if you could make it accurate enough. 2.5 ns is an awfully small time window to work with. Would using a prescaler on both signals work for you?

5. ### Cery Thread Starter New Member

Nov 27, 2014
7
0
Thanks Papabravo,
since my input signal is a sine wave with varying amplitude i wanted to create a Phase detector which is independent from the Amplitude.
I thought I would convert it to a square wave first to have constant high and low values and then XOR them together.

I'll think about using a prescaler. It might be a good solution for my project...
thanks,
Cery

6. ### Tesla23 Active Member

May 10, 2009
323
67
The Hittite HMC440 may help:

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7. ### Papabravo Expert

Feb 24, 2006
10,340
1,850
So how would you use a synthesizer as a phase detector?

8. ### Tesla23 Active Member

May 10, 2009
323
67
Just use the PFD. On the HMC440 though, I didn't realise that you couldn't reduce the VCO divider below 2, so you would have to add another /2 on the ref leg (essentially your prescaler).

I've no idea of the OP's application, but there are a number of logic-type phase detectors that work at RF. Years ago I used the AD9901, but this only goes to 200MHz and has crappy linearity past ±pi. Other devices include the MAX9382, MAX9383, SY100EP140 that go past 400MHz. He could just use a balanced mixer and drive it hard but you get limited phase range. Alternatively there are devices like the AD8302.

Last edited: Nov 29, 2014
9. ### Cery Thread Starter New Member

Nov 27, 2014
7
0
Sorry that I responded so slow,

I thought about using prescalers like you suggested Papabravo but unfortunately they would work worse the bigger the division.

Instead i think i'll try it with the logic-type phase detectors Tesla posted. The MAX9382 seems to be a good solution.
But if I do so I would still need to have a ADC to convert the signal right? Or would that work due to the integrated comparator?

Thanks a Lot!
Cery

10. ### Cery Thread Starter New Member

Nov 27, 2014
7
0
I've worked out a circuit for the phase-shift detection of my two analog sine wave signals.
What do you think, would this work? I haven't got a lot of experience with things like this.
If this would work which transistors do i need to choose?

I really appreciate any help!
Cery

(in1,in2 433Mhz)

11. ### Papabravo Expert

Feb 24, 2006
10,340
1,850
How are the PNP transistors biased?
How are the input signals coupled to the circuit?

12. ### Cery Thread Starter New Member

Nov 27, 2014
7
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The PNP transistors are Biased from top to bottom: Emitter - Base - Collector
I wanted to couple those input waves directly to the circuit. Would i need to couple it different?

13. ### Papabravo Expert

Feb 24, 2006
10,340
1,850
You obviously didn't understand the questions. So good luck getting it to work.
PNP transistors require DC biasing to put them into their linear range.
High frequency signals would normally be AC coupled. Direct coupling has problems.
Also, run of the mill PNP transistor won't work in this application.

14. ### Cery Thread Starter New Member

Nov 27, 2014
7
0
Sorry I didn't understood this simple Question.
But i hope i understand now. And now i also understand why my circuit wouldn't work this way.
I'm connecting my input signal directly to the Base so the BJT only conducts when my analog input signal is positive. I thought this would act like an ADC but unfortunately this wouldn't work because the saturated state is reached only when the input signal is High enough. Resulting in significant smaller high states then low states in the resulting digital square wave. I would need a BJT which reaches the saturated state with really low input voltages, with zero...
I guess there are even more flaws with that.
Thank you for helping,
Cery