I need to control and program the value of a mechanical variable capacitor (several pF ) in a closed loop. The attached block diagram shows the basic idea.
As depicted, I need an accurate oscillator with an external capacitor (as the control element) which acts similar to a VCO in the PLL. Parts like 74HCT9046A or CD4046B meet the requirement but they do not provide the flexibility of newer PLLs. Basically I prefer to use one of Analog Devices' PLLs to make use of various design tools, ANs, etc. I am not sure if such a device is available from the Analog! Other solutions might be available.
In short, I seek for any of the following solutions:
1- A VCO with external capacitor like the above mentioned components but with more features suitable for integrating with Analog PLLs.
2- A Capacitance-to-Frequency Convertor which can act like a VCO in the loop.
3- A Capacitance-to-Digital Converter (eg. AD7745/46/47) which can be used to control a Programmable Oscillator. So the series combination of CDC and digital programmable oscillator substitutes the VCO in the loop.
I appreciate any solutions, comments, and hints.
Thanks and Regards,
Message was edited by Shahrokh: It should be noted that due to actuator hysteresis, look-up table can not be used to set the capacitor value. Basically, this problem has led to the idea of using PLL.