* Question

What are the working principles of deep circuits?

* Answer

The working principle of deep transistor circuits can be explained from the perspective of amplifier stability and temperature dependence:

Amplifier Operation and Stability

In a typical deep circuit, the transistor (e.g., VT1) functions as the core amplifying element.

For an amplifier to operate stably, it requires a stable quiescent current (bias point). If the quiescent current shifts with external conditions, the operating point of the amplifier drifts, which directly affects gain, linearity, and overall performance.

Therefore, the base current of VT1 must remain steady even when environmental factors such as temperature change. Any significant fluctuation in base current leads to instability in the amplification process.

Temperature Dependence of the Transistor

A fundamental drawback of bipolar transistors is that their base current is temperature-dependent.

As the temperature rises, the carrier mobility and saturation current increase, causing the base current of VT1 to increase accordingly. Conversely, when the temperature falls, the base current decreases.

This relationship means that the transistor’s thermal stability is inherently poor if no compensation is applied. Without proper biasing techniques, the amplifier may suffer from thermal runaway, where increased temperature leads to increased current, which further raises the temperature, creating a destructive cycle.

Engineering Implication

To ensure reliable performance, deep amplifier circuits must include stabilization measures, such as thermal compensation networks, biasing resistors, or negative feedback.

These techniques minimize the influence of temperature on the base current, thereby maintaining a stable operating point and preventing distortion or damage.

Summary

In essence, the working principle of deep circuits is governed by the amplification behavior of transistors and their sensitivity to temperature. The amplifier requires a stable quiescent current, but because transistor base current naturally varies with temperature, temperature compensation and circuit stabilization techniques are essential to maintain consistent performance.