temperature compensation circuit

Thread Starter

ahmed55

Joined Apr 8, 2017
40
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 3.3v.Which temperature compensation circuit must be used with this oscillator ?



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Thread Starter

ahmed55

Joined Apr 8, 2017
40
no but i must use a temperature sensor like AD590 but this sensor have a power supply +5 V , my circuit must have 3.3 V ! below an oscillator with a temperature sensor
 

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WBahn

Joined Mar 31, 2012
26,398
So you ask what temperature compensation circuit you must use without telling us that you are constrained to use a temp sensor "like" an AD590.

Can't wait to see what other constraints you are going to trickle out as people base their responses on the incomplete information you've given up to that point.
 

Thread Starter

ahmed55

Joined Apr 8, 2017
40
ok i'm working in capacitive sensor for soil moisture using FDR technique or capacitance technique to detrmine the permittivity of soil . this capacitance sensor is sensitive to temperature variation , so i must use a temperature sensor to compensate temperature variation and to keep oscillator frequency output invariable or insensitive to temperature variation
 

Thread Starter

ahmed55

Joined Apr 8, 2017
40
@WBahn i said i want to use a sensor like AD590 because the power supply of this sensor is +5 V min or my circuit power supply is 3.3 V
 

WBahn

Joined Mar 31, 2012
26,398
because my sensor is sensitive to conductance and the effect of condcutance decrease at 100 MHZ
Huh? Why does that make you NOT want to start with a good, stable, temperature-compensated oscillator to begin with?

This is like someone asking how to improve the suspension of their quarter-ton pickup so that they can haul a two-ton load. When someone asks why they don't just get a deuce-and-a-half they then say it's because they want to haul heavy things.
 

Thread Starter

ahmed55

Joined Apr 8, 2017
40
i'm working with Clapp oscillator which was chosen for its temperature stability but thermal compensation circuit must be added to compensate temperature change in soil
 

wayneh

Joined Sep 9, 2010
17,153
i'm working with Clapp oscillator which was chosen for its temperature stability but thermal compensation circuit must be added to compensate temperature change in soil
Do you not see the oxymoron? If you need to apply compensation, then it is NOT a good choice for temperature stability. You need a temperature-stable oscillator, right? There is such a thing and it's not your Clapp oscillator.
 

WBahn

Joined Mar 31, 2012
26,398
i'm working with Clapp oscillator which was chosen for its temperature stability but thermal compensation circuit must be added to compensate temperature change in soil
So are you claiming that a Clapp oscillator is more temperature stable than an oven-controlled crystal oscillator? If not, then why did you not choose it instead?
 

crutschow

Joined Mar 14, 2008
27,770
How are you detecting the change in capacitance of the soil sensor?
Is it one of the capacitors in the oscillator circuit?
Is it that you need the oscillator to change frequency with the soil temperature?

If you insist on telling us want you want, not what the system requirements are, it's just a game of 20 questions. :rolleyes:
 

Thread Starter

ahmed55

Joined Apr 8, 2017
40
the change in capacitance of the sensor will be detecting by the change of the capacitance of the electrodes which make part of the LC oscillator , and the oscillator frequency change by electrodes capacitance . the measurement is sensitive to soil temperature so we need thermal compensation circuit
 

MrAl

Joined Jun 17, 2014
8,483
Hello,

Let me try to clear this up.

Your sensor is capacitive, and the change in capacitance is due to moisture AND temperature, but you want to eliminate or reduce the sensitivity to temperature so that you detect only changes in moisture.

Does that sound correct?

Also, this is in the homework section so you are probably not free to change the circuit any way you wish but must follow a given set strategy.
 
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