Overview on Analog circuits
Comparison between FET and BJT
Advantages of FET
• The BJT transistor is a current-controlled device ,whereas the JFET
transistor is a voltage-controlled device.
• The most important characteristics of the FET is its high input
impedance(>1MΩ).
• FETs are more temperature stable and less noiser than BJTs.
• FETs are usually smaller than BJTs, making them particularly useful
in integrated-circuit (IC) chips.
• Disadvantages of FET :
• They are more costly than junction transistor.
• Smaller gain bandwidth product compare to BJT.
• Transconductance is low hence voltage gain is low.
Classification of FET’s
JFET
• Symbols
Shockley’s Equation
Structure of n-Channel JFET
Drain characteristics of JFET
Transfer characteristics.
MOSFET
Depletion type N channel MOSFET
Enhancement type N channel MOSFET
Depletion Type
Enhancement Type
BJT AMPLIFIERS
CE Amplifier
CB amplifier
CC Amplifier
Comparison Table
Darlington Transistor
For obtaining high input resistance and low output resistance
Cascode amplifier
• The Cascode amplifier is the two stage amplifier in which common
emitter stage is connected to common base stage.
It offers
• High gain, wider bandwidth, improved
linearity, and higher output impedance
compared to single-stage amplifiers.
• It is commonly used in high-frequency
applications.
Feedback amplifiers
Advantages and disadvantages of negative feedback
Advantages
1.Improvement in the input impedance.
2. Better stabilized voltage gain.
3. Improved frequency response and bandwidth.
4. Improvement in the output impedance.
5. Reduced noise.
6. More linear operation.
Disadvantage
• Gain is reduced
Applications of positive and negative feedback
• Positive (regenerative) feedback used in oscillators .
• Negative (degenerative) feedback used in amplifiers.
Basic amplifiers types
Types of negative feedback amplifiers
1. Voltage-series feedback
2. Voltage-shunt feedback
3. Current-series feedback
4. Current-shunt feedback
• EXAMPLE : Determine the voltage gain, input, and output impedance with
feedback for voltage-series feedback having A = -100, Ri = 10 k Ω, and Ro =
20 kΩ for feedback of β =0.1.
oscillators
RC PHASE SHIFT OSCILLATOR
WEIN BRIDGE OSCILLATOR
LC OSCILLATORS
Colpitts Oscillator
Hartley Oscillator
Crystal Oscillator
• It is based on Piezo electric effect.
Quartz Crystal Equivalent Model