Temperature compensation circuit

[AHMEDbr]

Homework Statement

I am designing a local oscillator ( clapp ) whose frequency needs to be kept constant even with varying temperatures , this oscillator have an output frequency 150 MHZ , and power supply 3.3 V

Homework Equations

which temperature compensation circuit must be used with this oscillator ?

The Attempt at a Solution

 

[berkeman]

Homework Statement

I am designing a local oscillator ( clapp ) whose frequency needs to be kept constant even with varying temperatures , this oscillator have an output frequency 150 MHZ , and power supply 3.3 V

Homework Equations

which temperature compensation circuit must be used with this oscillator ?

The Attempt at a Solution

What are your thoughts? What component values or qualities vary in that circuit with temperature?

 

[AHMEDbr]

the JFET and all the others components because I'm working in HF also i will use electrodes in parallel with C3 for measure soil moisture , and the measurement is sensible to temperature variation

 

[berkeman]

the JFET and all the others components because I'm working in HF also i will use electrodes in parallel with C3 for measure soil moisture , and the measurement is sensible to temperature variation

So what are your initial thoughts to be able to do temperature compensation? What-all changes in the FET? Are you supposed to ignore the tempcos of the capacitors and other passives?

 

[gneill]

I don't see any design target for temperature stability. What is an acceptable range for the oscillator frequency?How do you plan on measuring or calculating it?

What's the anticipated operating temperature range? How does your existing circuit behave over that range? (so how much effort do you need to put into make it conform to requirements?)

Would you change the oscillator circuit type if you find that the required compensation is too complex to be practical?

 

[AHMEDbr]

i can use à temperature sensor with a voltage controlled capacitor to compensate temperature , i found in net analog device AD590 but it power supply is +5 V , my circuit power supply is 3.3 V so i must use another temperature sensor

 

[AHMEDbr]

below is an example of thermal compensation circuit

 

[Nidum]

Why not just use a crystal oscillator ?

 

[AHMEDbr]

because the oscillator will have a variable frequency output , so crystal oscillator is not the best choice

 

[berkeman]

because the oscillator will have a variable frequency output , so crystal oscillator is not the best choice

That's what crystal-based synthesizer ICs are for. Have you looked at them yet?

 

[AHMEDbr]

not yet ...