Common Emitter Configuration and Collector Curve
- 1. Developed By: Zeeshan Rafiq
- 2. BJT Common Emitter & Collector Curve Presentation Topic:- Zeeshan Rafique (16201519-026) Muhammad Abbas (16201519-001) Muhammad Umar (16201519-099) Zaid Khalid (16201519-106) Developed By: Zeeshan Rafiq
- 3. COMMON EMITTER • It is called common-emitter configuration since : - emitter is common or reference to both input and output terminals. - emitter is usually the terminal closest to or at ground potential. • Almost amplifier design is using connection of CE due to the high gain for current and voltage. • Two set of characteristics are necessary to describe the behavior for CE ;input (base terminal) and output (collector terminal) parameters. • This circuit has two loops. The Left Loop is the base loop & the right loop is the collector loop. • Note: The current relation are still applicable IE=IC+IB & IC= b IB Developed By: Zeeshan Rafiq
- 4. Input characteristics:- Input takes the form of a forward biased pn junction. Input characteristics are therefore similar to those of a semiconductor diode. Output Characteristics:- Input characteristics Graph The magnitude of IB in micro ampere and not as horizontal as IE in common-base circuit. The output set relates an output current IC to an output voltage VCE for various level of input current IB. There are three portions as shown in Next Slides:- Developed By: Zeeshan Rafiq
- 5. COMMON EMITTER • Active Region: The active region, located at upper-right quadrant, has the greatest linearity.() The curve for IB are nearly straight and equally spaced. In active Region, B-E junction is forward Biased.. • Cutoff Region The region below IB =0UA is defined as cutoff region. • Saturation Region The small portion near the ordinate, is the saturation region, which should be avoided for linear amplification In the dc mode, the level of IC and IB at the operation point are related by: Normally B ranges from 40 to 400 Active Region Saturationregion Collector output Graph Developed By: Zeeshan Rafiq
- 6. Common Emitter Configuration (Base Biases) • In the base loop, the VBB source biased the emitter diode with RB as a current limiting resistance. • By changing VBB or RB ,we can change the base current. So base current will change the collector current. • It means that small current(BASE) will produce large current (Collector). • In the collector loop, a source voltage VCC reverse biases the collector diode through RC . Double scripts notation is used with transistor circuit. When the subscript is same, represent a source(VCC)(VBB) Single scripts are used for node voltages, that is, voltages between the subscript point and ground(reference). In CE (BaseBiase) Connection, dc current gain beta exist which can be change overall output. By applying simple KVL, we can find Output VoltagesAt input side: IB = VBB - VBE RB Now at Output side: VCE=VCC-ICRC & .’. IC=BIB Developed By: Zeeshan Rafiq
- 7. Current Gain Beta dependency:- • Itself transistor • Collector Current • Temperature Due to Beta dependency in Base Bias we avoid some case to use in it amplifier circuit. So we use another configuration. Developed By: Zeeshan Rafiq
- 8. Common Emitter Configuration (Emitter Bias) • Digital circuits are the type of circuits used in computers. In this area, Base bias and circuits derived from base bias are useful. • But when it comes to amplifiers, we need circuits whose Q points are immune to changes in current gain. • As you can see, the resistor moved from base circuit to the emitter circuit. That one make change all over the world. Q point have greater less effect due to current gain • BASIC IDEA • Base supply voltage directly applied to base and trouble shooter will read VBB BW Base and Ground. • Now emitter is above the ground and has a voltage given by: VE=VBB-VBE IE=( VBB-VBE ) R E • Now we Find Collector Voltage By KVL at output sideVCE=VCC-IC(RC+RE) IE=~ IC IC=( VBB-VBE ) R E We can draw from this formula a load line Developed By: Zeeshan Rafiq
- 9. Minor effect of Current Gain factor • This current gain has minor effect on the collector current. Under applying all operating conditions, the three currents are related by: • IE=IC+IB Which can be rearranged as: IE=IC+(IC+IC/Bdc ) Developed By: Zeeshan Rafiq
- 10. COLLECTOR CURVE This set of curves is also called a family of curves. • When VCE is zero, the collector diode is not reverse bias. This is why, graph shows a collector current of zero when VCE is zero. • When VCE is increasing from Zero, the collector current rises sharply. • When VCE is few tenths of a volts, the collector current becomes almost constant and equal to 1mA. Developed By: Zeeshan Rafiq