SAW Sensor - Why is my circuit not oscillating?

[saviobezerra]

First, sorry for my bad english.

I'm building a project using a Colpitts Oscillator with Differential Pair, designed for ~117.6MHz. I'm using LTspice for simulation. The oscillator individually oscillates, but I need it to oscillate when I add a sensor model (as seen in the image in the circuit's feedback loop). When I add the sensor it initially wobbles and then stops, any ideas how I can fix this?

 

[FvM]

I merged the new post with the previous thread. The question was basically answered two months ago. An oscillating configuration was suggested.

There are essentially two points
- resonator has 180° phase shift and needs non-inverting amplifier configuration
- need to achieve sufficient gain and impedance matching

 

[Audioguru]

Frequently a simulated oscillator needs to be kicked to get it started. The kick in a real circuit is an input pulse that is produced with noise or a power-on voltage surge.