I followed the MAX2606 VCO circuit connection, but it only has a DC output of around 3.8V. Then, the output is not entirely a DC voltage; there's a fluctuation of about 80mV. The supply voltage is 4.2V.

The inductor L1 in this circuit has been selected according to the datasheet, and a 480 nH inductor is used.

This issue has stumped me for a long time without resolution. If you could give me some advice, it would be incredibly valuable. Thank you very much!

 

hi nanji,
Please post your LTSpice asc file and the MAX model.
E

 

There is no mention of LTspice in this thread or in any other threads initiated by the TS.
Where did you come up with the circuit represented by your schematic? Why is the TUNE input not connected to a DC control voltage?

 

It does seem that there should be a resonant (LC) circuit, and what the tune connection requires is not hinted at even. So the fist step is to see what the manufacturer's application information suggests.
The second consideration is that the physical arrangement in an RF oscillator circuit is rather critical.

 

I think there should be a voltage applies to pin-3.

 

If it is a VCO intended for use in a Phase Locked Loop system then certainly there needs to be a frequency control voltage input. Possibly not an external resonant circuit, but that will depend on exactly what the internal circuit is. So that means back to the full data sheet and the manufacturer's application notes. App-notes can be very valuable. Go to the maxim semiconductor website or just do a search for that part number. and ignore yootoob sites.
The actual data sheet shows that your posted schematic may not possibly function. There needs to be a voltage present at the "tune" connection.

 

It does seem that there should be a resonant (LC) circuit, and what the tune connection requires is not hinted at even. So the fist step is to see what the manufacturer's application information suggests.
The second consideration is that the physical arrangement in an RF oscillator circuit is rather critical.

The datasheet is clear that a DC voltage between +0.4 and +2.4 volts is required on the tune pin. This is applied to the cathode of a varactor that is the variable capacitance in the oscillator's resonant tank circuit.