This single stage BJT (bi-polar junction transistor) stage has been bench tested to verify that the design works. Specifications are given below. Use a trim pot for R1 to bias the circuit.
BJT STAGE SPECIFICATIONSThe gain AV for this circuit, unloaded, is about 16db or 6.3 volts per volt. Is is the current draw in microAmps. Voltages for collector, emitter and base, VC, VB, and VE, are all given. Resistor values are given with notes. Input impedance, Zin, and output impedance, Zout, are also given. Notice that the input impedance, is pretty low at 4.8 kohm. RL = open represents my oscilloscope probe resistance at 1 Mohm.
Specifications for this stage:
AC GAINAlso notice that the AC gain AV V/V drops quickly once a real load has been placed for "RL". Notice that with a load of 5 kohms you only get about 6db of gain. Load value matters.
SPICE DC VOLTS
The circuit draws about 700 micro amps from the supply. Notice that the collector voltage is set to 1/2 VCC, or 4.5 VDC. SPICE simulation agreed fairly well with the real bench tested circuit.
HIGH BETA TRANSISTORThe transistor used in this example is an NPN 2N5089 with a Beta greater than 300. Almost any transistor with a Beta greater than 300 should bias up pretty close this this circuit with a little adjustment of the trim pot.
ADJUSTING BIASAdjusting bias is easy when you use a quality potentiometer. I use Bourns pots for prototyping.
Thanks for reading,