12 Feb The collector-base junction is reverse-biased . . .’ That is true for all transistor amplifiers, regardless of biasing method. ‘Due to the negative feedback loop created between the emitter
"The collector-base junction is reverse-biased . . ."
That is true for all transistor amplifiers, regardless of biasing method.
"Due to the negative feedback loop created between the emitter and the collector . . ." — and — "A negative feedback effect is produced by the voltage drop across the collector-base junction . . ."
The collector pin and CB PN junction are not part of the negative feedback mechanism for an emitter biased transistor. What is really happening to produce the negative feedback?
"Base bias, on the other hand, is less stable than emitter bias since it is dependent on a single forward-biased junction."
Only the BE PN junction is forward biased in all transistor amplifiers. What is the real reason that base biased transistors are affected more by changes in beta than emitter biased transistors? I think you misunderstood what Boylestad and Nashelsky wrote.
"the Q-point shift caused by temperature is more pronounced in base bias topologies because there is only one forward-biased junction in the base bias configuration, which makes it more sensitive to temperature fluctuations,"
All transistor amplifiers have only one forward-biased PN junction — the base-emitter junction. The collector-base junction is always reverse biased. This does not affect stability. What is really happening?
"Emitter-feedback bias has the additional benefit of doing away with the separate biasing resistor that base bias systems frequently ask for."
Base bias circuits always have a base resistor, but no emitter resistor.
Emitter bias circuits usually have an emitter resistor, but no base resistor. The number of components is the same, so a lower component count is not an "improvement". What is?
Emitter Bias Report
Why is emitter bias more stable than base bias?
Due to the negative feedback loop created between the emitter and the collector, emitter bias is more stable than base bias. The collector-base junction is reverse-biased, resulting in a voltage drop, and the emitter-base junction is forward-biased, allowing a significant current flow through the emitter. A negative feedback effect is produced by the voltage drop across the collector-base junction, which stabilizes the current flow through the emitter and lessens the sensitivity to variations in temperature and other environmental conditions. Base bias, on the other hand, is less stable than emitter bias since it is dependent on a single forward-biased junction (Boylestad & Nashelsky, 2017).
Explain why the base bias Q-point changes with temperature.
Bipolar junction transistor (BJT) base bias Q-point (operating point) changes with temperature as a result of variations in the forward-biased base-emitter junction voltage (VBE). The base current (IB) and the collector current of a BJT are influenced by temperature variations in the VBE, which is temperature-sensitive (IC). The Q-point shift brought on by the change in VBE and the consequent changes in IB and IC affect the transistor's gain, output voltage, and overall performance. Compared to emitter bias, the Q-point shift caused by temperature is more pronounced in base bias topologies because there is only one forward-biased junction in the base bias configuration, which makes it more sensitive to temperature fluctuations, (Sedra & Smith, 2015).
How does emitter-feedback bias improve on base bias?
Bipolar junction transistors (BJTs) frequently use emitter-feedback bias, also referred to as self-bias, as a biasing method because it offers greater stability and precision than base bias.
A portion of the collector current is supplied to the emitter terminal during emitter-feedback bias, resulting in a negative feedback loop. This negative feedback loop reduces the sensitivity to variations in temperature and other environmental conditions while stabilizing the current flow through the emitter. A more stable Q-point is produced due to the voltage drop across the collector-base junction, which produces a negative feedback effect to counterbalance variations in the base-emitter junction voltage (VBE) (Boylestad & Nashelsky, 2017).
Emitter-feedback bias has the additional benefit of doing away with the separate biasing resistor that base bias systems frequently ask for. In an emitter-feedback bias circuit, the emitter resistor supplies both the necessary bias current and the feedback voltage that keeps the circuit stable. This makes the biasing technique more effective by streamlining the circuit design and lowering the number of components needed.
References
Boylestad, R. L., & Nashelsky, L. (2017). Electronic devices and circuit theory. Pearson.
Sedra, A. S., & Smith, K. C. (2015). Microelectronic circuits (7th ed.). Oxford University Press.
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