Module 1
DC Biasing of BJT Circuits
Dr SATHYA P
Associate Professor
SENSE
Introduction
• A transistor must be dc biased in order to operate as an amplifier.
• The term biasing refers to the application of dc voltages to establish a
fixed level of current and voltages in a circuit.
• The resulting dc voltage and current establish an operating point on
the characteristic curve that defines the region employed for
amplification of input signal.
• Q point is also called as quiescent point.
Operating point
Types of Biasing
• Fixed bias method
• Collector to base bias method
• Emitter stabilized bias
• Voltage divider bias
• Constant current bias
Fixed bias/ Base bias method
Emitter Stabilized Bias
Collector to Base Bias
Voltage Divider Bias
Self bias/VDB
IE = I B + I C
Collector–Emitter Loop:
Load Line points
• The output load line equation is given by
• Put IC = 0, VCE (max) = VCC
• Put VCE = 0, IC (max) = VCC / (RC + RE)
• X axis points: (VCE(max), 0)
• Y axis points: (0, IC(max))
• Numerical 1:
Determine the collector-emitter voltage in the voltage divider bias circuit shown
and plot the Q point. Assume β = 100.