Effect of Finite Slope of the Transistor Output Characteristic
by Kenneth L. Ashley
Analog Electronics with LabVIEW®
- Copyright
- National Improvements | Virtual Instrumentation Series
- Preface
- References
- Hardware and Software Requirements
- LabVIEW VI Libraries and Project and Problem Folders and Files
- Elementary Circuit Analysis for Analog Electronics
- Transistors and Voltage Amplification
- Characterization of MOS Transistors for Circuit Simulation
- Signal Conductance Parameters for Circuit Simulation
- Common-Source Amplifier Stage
- Coupling and Bypass Capacitors and Frequency Response
- MOSFET Source-Follower Buffer Stage
- MOSFET Differential Amplifier Stage
- DC (Bias) Circuit
- DC Imbalances
- Signal Voltage Gain of the Ideal Differential Amplifier Stage
- Effect of the Bias Resistor on Voltage Gain
- Differential Voltage Gain
- Common-Mode Voltage Gain
- Voltage Gains Including Transistor Output Resistance
- Body Effect and Voltage Gain
- Amplifier Gain with Differential and Common-Mode Inputs
- Comparison of Numerical Gain Results
- Summary of Equations
- Exercises and Projects
- MOSFET Current Sources
- Common-Source Amplifier with Current-Source Load
- Operational Amplifiers with Resistor Negative Feedback
- Operational Amplifier Applications with Capacitors
- Cascaded Amplifier Stages
- Combining NMOS and PMOS Circuits in Cascade
- Amplifier Gain of Differential Amplifier and Common-Source Stage in Cascade
- Stabilization of Signal Gain and Bias Current with a Source Resistor
- Common-Source Stage as a Series – Series Feedback Circuit
- Shunt – Series Cascade Amplifier
- Summary of Equations
- Development of a Basic CMOS Operational Amplifier
- Current-Source Bias for the Differential Amplifier Stage
- Current-Source Output Resistance and Common-Mode Gain
- Current-Source Load for the Common-Source Stage
- Current-Source Load for the Differential Stage
- Two-Stage Amplifier with Current-Source Biasing
- Output Buffer Stage
- Output Resistance of the Feedback Amplifier and Effect on Gain from Loading
- Output Circuit of the TS271 Opamp
- Summary of Equations
- Communicating with the Circuit Board: LabVIEW Programming and Measurement Exercises
- Characterization of the Bipolar Junction Transistor for Circuit Simulation
- Fundamentals of Bipolar Junction Transistor Action
- Base-Width Dependence on Junction Voltage
- BJT Base, Emitter, and Collector Currents in the Active Mode
- Diode-Connected Transistor Circuits for Measuring Base and Collector Current
- Output Characteristics of BJT in the Common-Emitter Mode
- SPICE Solution for IC versus VCE of the Measurement Circuit
- Collector-Emitter Voltage and Collector Current in the Saturation Region
- SPICE BJT βDC as a Function of Collector Current
- Signal or Incremental Common-Emitter Current Gain
- Summary of Equations
- Exercises and Projects
- Common-Emitter Amplifier Stage
- DC (Bias) Analysis
- Linear or Signal Model for the BJT
- Amplifier Voltage Gain
- Accuracy of Transistor Gain Measurements
- Effect of Finite Slope of the Transistor Output Characteristic
- Selection of Coupling Capacitors
- Common-Emitter Amplifier with Active Load
- Frequency Response of NPN – PNP Amplifier Due to the Base Shunt Capacitor
- Common-Emitter Stage with Emitter Resistor and the Emitter-Follower Amplifier Stage
- Summary of BJT Model Parameter Relations
- Summary of Circuit Equations
- Exercises and Projects
- Basic Circuit Analysis for Electronic Circuits and Programming Exercises
- Basic NMOS Common-Source Amplifier with Programming Exercises
- Characterization of the PMOS Transistor for Circuit Simulation
- Characterization of the NMOS Transistor for Circuit Simulation
- PMOS Common-Source Amplifier
- PMOS Common-Source Amplifier Stage with Current-Source Biasing
- NMOS Common-Source Amplifier Stage with Source-Resistor Bias
- NMOS Source-Follower Stage
- MOSFET Differential Amplifier Stage
- Current Mirror and Common-Source Amplifier with Current-Source Load
- Operational Amplifier with Resistor Feedback
- Operational Amplifier Integrator and Oscillator
- Communicating with the Circuit Board Using the DAQ
- Sending and Receiving Voltages with the Sending and Receiving VIs
- Sending and Receiving Voltages from the Front Panel
- Plotting Measured Samples
- Using the Autoranging Voltmeter
- Observing the Oscilloscope Output Graph
- Discrete Output Voltage from the DAQ
- Discrete Input Voltage from the Circuit Board
- Using the Simultaneous Sending/Receiving Function
- Characterization of the Bipolar Junction Transistor for Circuit Simulation
- NPN Common-Emitter Amplifier
- NPN – PNP Common-Emitter Amplifier with Current-Source Load
C.5. Effect of Finite Slope of the Transistor Output Characteristic
As discussed in Unit C.2, the signal model contains an output resistance, which reflects the fact that the output characteristic of the transistor has a finite slope. This is characterized with the SPICE parameter VAF. It was noted that the effect of the finite slope is to place a resistance effectively across the output of the amplifier. It is calculated from ro = VAF/IC, (C.13).
With increasing bias current, ro may not be negligible compared to RC. In the project on the gain of the amplifier, we will read the experimental data into a Mathcad file and adjust VAF to make the SPICE calculation and measured data match. The gain expression that includes transistor output resistance is
Equation C.28
In a representative transistor, VAF ≈ 100. The circuit design could call for ICRC ≈ 5 V for a 10-V supply voltage. In this case, the output resistance has about a 5% effect on the gain value.
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