# Temperature compensation circuit

1. Apr 11, 2017

### AHMEDbr

1. The problem statement, all variables and given/known data
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

2. Relevant equations
which temperature compensation circuit must be used with this oscillator ?

3. The attempt at a solution

#### Attached Files:

• ###### clapp oscillator circuit.PNG
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2. Apr 11, 2017

### Staff: Mentor

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

3. Apr 11, 2017

### 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

4. Apr 11, 2017

### Staff: Mentor

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?

5. Apr 11, 2017

### Staff: Mentor

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 in to 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?

6. Apr 11, 2017

### 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

7. Apr 11, 2017

### AHMEDbr

below is an example of thermal compensation circuit

#### Attached Files:

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8. Apr 11, 2017

### Nidum

Why not just use a crystal oscillator ?

9. Apr 11, 2017

### AHMEDbr

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

10. Apr 11, 2017

### Staff: Mentor

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

11. Apr 11, 2017

not yet ...