The main contents of the chapter consist of the following: Voltage biasing scheme, biasing by fixing voltage, biasing with feedback resistor, current-source biasing scheme. | Dr. Nasim Zafar Electronics 1 - EEE 231 Fall Semester – 2012 COMSATS Institute of Information Technology Virtual campus Islamabad Lecture No. 31 Biasing in MOS Amplifier Circuits and Single-Stage MOS Amplifiers 12/5/2012 Dr. Nasim Zafar. 2 Biasing in MOS Amplifier Circuits Lecture No. 31 Contents: Voltage biasing scheme Biasing by fixing voltage Biasing with feedback resistor Current-source biasing scheme 12/5/2012 Dr. Nasim Zafar. 3 Lecture No. 31 Biasing in MOS Amplifier Circuits Reference: Chapter Microelectronic Circuits Adel S. Sedra and Kenneth C. Smith. 12/5/2012 Dr. Nasim Zafar. 4 Introduction An essential step in the design of a MOSFET amplifier circuit is the establishment of an appropriate dc operating point for the transistor. This is the step known as biasing or bias design. 12/5/2012 Dr. Nasim Zafar. 5 Biasing by Fixing VGS The most straightforward approach to biasing a MOSFET is to fix its gate-to-source voltage VGS to the value required to provide the desired ID. ID = 1/2kn’(W/L)(VGS-VT)2 () However, Biasing by fixing VGS is not a good technique. 12/5/2012 Dr. Nasim Zafar. 6 Disadvantages of fixed biasing The use of fixed bias (constant VGS) can result in a large variability in the value of ID. Fixing biasing may result in large ID variability due to deviation in device performance Current becomes temperature dependent Thus, Unsuitable biasing method 12/5/2012 Dr. Nasim Zafar. 7 Biasing using a Fixed Voltage at the Gate and a Resistance in the Source An excellent biasing technique for discrete MOSFET circuits consists of fixing the dc voltage at the gate, VG, and connecting a resistance in the source lead, as shown in (a). For this circuit we VG=VGS+RS ID () Resistor Rs provides negative feedback, which acts to stabilize the value of the bias current ID. Rs gives it the name degeneration resistance. 12/5/2012 Dr. Nasim Zafar. 8 Biasing using a Fixed Voltage at the Gate , VG and a Resistance in the Source Figure (b) . | Dr. Nasim Zafar Electronics 1 - EEE 231 Fall Semester – 2012 COMSATS Institute of Information Technology Virtual campus Islamabad Lecture No. 31 Biasing in MOS Amplifier Circuits and Single-Stage MOS Amplifiers 12/5/2012 Dr. Nasim Zafar. 2 Biasing in MOS Amplifier Circuits Lecture No. 31 Contents: Voltage biasing scheme Biasing by fixing voltage Biasing with feedback resistor Current-source biasing scheme 12/5/2012 Dr. Nasim Zafar. 3 Lecture No. 31 Biasing in MOS Amplifier Circuits Reference: Chapter Microelectronic Circuits Adel S. Sedra and Kenneth C. Smith. 12/5/2012 Dr. Nasim Zafar. 4 Introduction An essential step in the design of a MOSFET amplifier circuit is the establishment of an appropriate dc operating point for the transistor. This is the step known as biasing or bias design. 12/5/2012 Dr. Nasim Zafar. 5 Biasing by Fixing VGS The most straightforward approach to biasing a MOSFET is to fix its gate-to-source voltage VGS to the value required to provide the desired .
