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Common Collector (CC) or Emitter Follower 5) Resistance Reflection Rule (RRR): The resistor looking into base is (β+1) times the total resistance in the emitter. Basically, there are three types of amplifier: 1.

Then, the amplifier can be replaced by its equivalent circuit model. #   vo RE R’L vbe gmvbe - + vb ib vo RE vbe gmvbe R’L - + R’s RC 4) An amplifier is characterized by: (a) Gain: voltage gain ( i o v v v A  ) current gain ( i o i i i A  ) (b) Input resistance (c) Output resistance. 3) Transistor must be biased in middle of active region to allow for maximum signal swing at the output. #  Revisit 1) Small signal AC equivalent circuit of BJT   beT  T be v v v v 1 vbe 5 mV or up to 5mV  vi 10 mV 2) The model is the same for npn or pnp transistor since the signal of interest is ac signal. vs 0 vbe 0 The dependent current source vg bem will be open circuit RO = RC (iv) Finding current gain #  B S B s E m L s o s B S B s E m L s s E m L o s E s be s m E be m E s s be m be E be s be be s sb be b m be E O m be L R R R R r R r g R voltage gain v v v R R R R r R r g R v R r R g R r v R r R v r v R r g r R r v g R r r R v v g v R r V R v r v v Ri v i gV R v g v R                                                   1( ) 1( ) 1( ) 1( ) ) ] 1 (iii) Finding output resistance RO = the resistance seen by RL First, short circuit the input voltage source. (i) Finding the voltage gain Apply Thevenin: R’s We assume all capacitors are short circuit (small impedances) in ac analysis. # 12V 6k 1k VCC Rs vs vo C 4k 1k RL= 1k C #  BCJ is reverse confirming that BJT is working in active 2. DC Analysis: Assume the transistor operates in active mode Apply Thevenin between base and ground: BJT - Introduction to AC Analysis ElectronX Lab 39.9K subscribers Subscribe 1.8K 226K views 11 years ago Bipolar Junction Transistors This video gives a description of what AC analysis is. short ckt DC voltage sources and open ckt DC current sources) Perform circuit analysis (EE201) 5. Also, set all independent sources to zero (i. #  Replace the transistor by its model 3.Draw the complete ac ckt assuming all capacitors short ckts 4. All capacitors open ckt ind IC and check that the transistor F s working in active mode i Calculate the ac model parameters. the load CE is called bypass capacitor 2. C1 and C2 are called coupling capacitors preventing any dc to go to the source and. 6-17.Example #1 Find the gain of the BJT amplifier (vo/vi) Observations: 1. …Ĭommon Emitter Amplifier Circuit : Consider the Common Emitter Amplifier Circuit circuit shown in Fig. Input impedance For frequencies in the midrange <100khz of a BJT transistor amplifier. The circuit uses voltage divider bias to derive the transistor base voltage (VB) from the supply. ohmeter cannot be used to measure the small signal ac input impedance. Learn Bipolar Junction Transistors (AC Analysis) equations and the formulas for Bipolar Transistor Configurations such as Fixed-Bias Configuration & more. 6-28 the external load (RL) is capacitor-coupled to the transistor emitter terminal. Also, there …Ĭommon Collector Circuit Analysis : In the Common Collector Circuit Analysis (CC) shown in Fig. 6-34 is very similar to a CE circuit, except that the input signal is applied to the transistor emitter terminal (via C2), instead of the base. RE must also be shown in the …Ĭommon Base Circuit Diagram : The Common Base Circuit Diagram (CB) shown in Fig. 6-25(a), it is also present in the ac equivalent circuit. The cascode has marginally better mid-band gain. AC DEC 10 1k 100Meg Note the ac 1 is necessary at the end of the V3 statement.

The SPICE statements responsible for the AC analysis, extracted from the listing: V3 4 6 SIN(0 0.1 1k) ac 1. CE Circuit with Unbypassed Emitter Resistor : h-parameter Equivalent Circuit – When an CE Circuit with Unbypassed Emitter Resistor (RE) as shown in Fig. Figure above shows the frequency response to both the cascode and common-emitter amplifiers.