mixer used in gps
PLL is a digital circuit. So when VCO output is mixed with analog RF signal , what type of signal do we have. Is the Mixer a modulator? What is the ultimate IF frequency signal we are getting?
Is VCO output digital or analog?
Is the receiver a digital or analog or mixed?
Can you send me some papers/notes explaining block wise operation of GPS receiver?
Thanx in advance
swagata
VCO output is a low swing sine signal, and it is mixed with rf signal after LNA, then generate the IF about 1M~4M Hz, then this signal will flow throuth band-pass filter and AGC and ADC,
So you can only get the digital signal after ADC.
The receive is a RF and mix-signal circuit.
I am having a 1.5GHz signal with 1.023 Mbps BPSK modulation as RF input and LO at 1.4 Gz. Is the χ block a mixer or modulator? I heard that when 2 analog signals are mixed its a mixer and when 1 analog and digital signal signal is mixed its modulator.
If a PLL is locked at 1.4GHz ,doues that means its input signal is 1.4GHz?
Plz send relevant notes if possible.
Thanx in advance
swagata
Yes, you are right. But I think the X block is a system.
Mixer is one component of it.
RF signal is 1575.42MHz, so the PLL is locked at (1575.42MHz -1.023MHz).
These two signals are the input of Mixer, so the output is 1.023MHz.
But there are BPF, VGA and ADC to process this 1.023MHz analog signal, then output a digital signal.
When you say its a receiver, then you are doing down conversion & it is a mixer not modulator.
Modulation is done while transmitting signal.
Even if you mix two analog signal it can be modulator when Up conversion is process is there.
So mixer is modulator during upconversion.
I think I coundn't explain the problems.
1. The PLL is used in GPS receiver not as Frequency demodulator but to generate LO frequency 1.4GHz.The confusion is "PLL locked at 1.4Ghz " means refrence input to PLL is 1.4GHz?(Triple conversion using fixed LO frequency architecture)
2.I have read "PLL is used as LO & Clock generator in digital system".For the 1st stage mixer we have RF input (1.5GHz)& LO(1.4Ghz).Its double balanced open collector mixer.Now is it a mixer or modulator?
3. Since we have a VCO, does it ensures it's analog PLL? What about the Phase Dector then? Is it a multiplier?
So you mean to say is
You are using PLL as a VCO source & Other device for frequency multiplication(phase detector). am I correct?
Why 1.4Ghz LO frequency is choosen in this fixed LO frequency architecture?
Added after 8 minutes:
Phase detector is a part of PLL and not modulator.
1, the reference frequency to pll is tens MHz. and the VCO frequency must be divided by 192 for example, then compare with the reference frequency by PFD.
2, It is a mixer
3, All digital PLL+DCO has been designed by Ti.