Investigating the thermal stability of transistor circuits with a high input resistance

Conclusions

On the basis of the above experimental investigations it is possible to state the following. Taking into account the small size of the automatic device for measuring the vibration parameters during the drilling of boreholes and its subjection to considerable temperature effects, it is advisable to use a thermally-stable circuit with a high input resistance of 10 MΩ. The utilization of silicon transistors in this circuit provides completely adequate input resistance for working with piezoelectric vibration transducers up to a temperature of +100°C.

In case it is necessary to raise still further the circuit input resistance, it is advisable to use silicon transistors with a higher current gain β, which are in short supply (for instance, transistors P504, P504A, P505, and P505A).

The use of transistors with a larger β makes it possible to apply a deeper negative feedback, which raises the input impedance and improves the gain stability of the stage with respect to temperature effects. The above circuits can also be used in other measuring and electronic devices which are subjected to considerable ambient temperature effects.