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What is the difference between minicircuits VCO groups?

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minicircuits VCO

minicircuits have two VCO groups:

1-linear tuning
2-low noise, 5V tuning for PLL IC's

what is the difference? where each group is used?

can we used first groups with 5V-PLL ICs?
 

Re: minicircuits VCO

Linear tuning usually means that they are using a varactor diode that tunes roughly linearly with frequency, that is a delta 1 V yields pretty much the same delta F at both the low and high end of the operating band. So if you are sending data by FM, you can get pretty much the same frequency deviation independent of operating frequency.

Unfortunately, such diodes do not have as high a Q as normal diodes, so the phase noise will be 5-15 dB worse than a regular oscillator. If you are sending PSK or QAM, you might need the better phase noise.
 

Re: minicircuits VCO

I am using FM,FSK.

which group is better?(linear?)

Can we use group 1 with PLL ICs?
 

Re: minicircuits VCO

In general, the linear tuning oscillator is the ticket. FM modulation moves the frequency above and below a center frequency. If you analog modulate with a sine wave, you will get a uniform +/- deviation of the carrier. This will keep the baseband signal from getting distorted.

If you are digital modulating 2FSK it is less important, but there are some subtle variations. Lets say the VCO is NOT linear tuning. So when you put out a "1" the oscillator tunes up 5% in frequency from center, but when you put out a "0" the VCO tunes -7% in frequency. So where is the center frequency now? When being modulated, the center frequency appears to shift 1% down. When the modulation stops, the center frequency appears to shift back to the original "center". So what frequency do you tell the FCC your center is at? Hmmm.

A linear tuning VCO will keep the apparent center frequency the same if you are not modulating, or if you are modulating.
 

Re: minicircuits VCO

the 5V for PLL application is helpful ,because most of the frequency synthesise chip only gives a 0-5V output voltage of the charge pump. however , if the vco tune voltage is higher than 5v, active loop filter must be used,when an OP amp is used in the loop , there are other problems ,such as phase noise , power supply etc
 

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