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Cascode AmplifierModule Title: Analog and mixed signal circuit design                 Date: 2nd July 2012            M. S....
Contents• Introduction• Cascode amplifier• Small signal model• Gain calculation• Cascode Current mirror• Cascode different...
Multi-Stage Amplifiers (Cascading)• We can cascade different types of amplifiers to get desired overall   characteristics....
Introduction• Constructed using two transistors, one operating as CS and the other as   a CG• Best of both the circuit con...
Comparison of CSA with a Cascode amp                 RL=300k                        D             G                       ...
Cascode amplifierFigure 3. Cascode amplifier [Sharma 2010]    M. S. Ramaiah School of Advanced Studies   6
Waveforms for Cascode amplifier for varying load       Figure 4. Waveforms for change of output with respect to load      ...
Small signal modelFigure 5. Small signal model of cascode amplifier [Sharma 2010]              M. S. Ramaiah School of Adv...
Gain calculationFigure 6. Gain calculation [Sharma 2010]      M. S. Ramaiah School of Advanced Studies   9
Cascode Current Mirror  •   This circuit does not need an external voltage bias.  •   The reference side of the mirror gen...
Common-Source - Source-Follower Cascade                           RD                                               M2     ...
Cascode Differential amplifier•   Use of cascoding to increase load resistance•   Cascode both the active loads and the di...
Summary• Best of both the circuit configurations (common source and common   gate)• The cascode arrangement offers high ga...
References• Dinesh Sharma (2010) CMOS Mixed Signal Design: OpAmp Design        [online] available from < www.ee.iitb.ac.in...
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Seminar on Cascode amplifier

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  • The cascode improves input-output isolation (or reverse transmission) as there is no direct coupling from the output to input. This eliminates the Miller effect and thus contributes to a much higher bandwidth.
  • The cascode improves input-output isolation (or reverse transmission) as there is no direct coupling from the output to input. This eliminates the Miller effect and thus contributes to a much higher bandwidth.For the two-FET cascode, both transistors must be biased with ample VDS in operation, imposing a lower limit on the supply voltage.
  • the input signal of a common-gate stage may be a current. We also know that a transistor in a common-source arrangement converts a voltage signal toa current signal. The cascade of a CS stage and a CG stage is called a &quot;cascode&quot;&apos; topology
  • Stability: Its output is effectively isolated from the input both electrically and physically.
  • Transcript of "Seminar on Cascode amplifier"

    1. 1. Cascode AmplifierModule Title: Analog and mixed signal circuit design Date: 2nd July 2012 M. S. Ramaiah School of Advanced Studies 1
    2. 2. Contents• Introduction• Cascode amplifier• Small signal model• Gain calculation• Cascode Current mirror• Cascode differential amplifier• Conclusion• References M. S. Ramaiah School of Advanced Studies 2
    3. 3. Multi-Stage Amplifiers (Cascading)• We can cascade different types of amplifiers to get desired overall characteristics. Often want: – High input impedance – High gain – Low output impedance – Higher gain• Mix and match cascades of different types of amplifiers to get desired result M. S. Ramaiah School of Advanced Studies 3
    4. 4. Introduction• Constructed using two transistors, one operating as CS and the other as a CG• Best of both the circuit configurations namely, – Moderate input impedance and high voltage gain of CS configuration – Very large output impedance, large output voltage swing and much larger band width of CG configuration.• Disadvantage: Requires two transistors and a relatively high supply voltage.• Applications: Used in current mirrors to increase output impedance, as a modulator for amplitude modulation, M. S. Ramaiah School of Advanced Studies 4
    5. 5. Comparison of CSA with a Cascode amp RL=300k D G M1VGS1=0.6V S 5u/0.35u vout vin Figure 1. Common source amplifier [Sharma 2010] Figure 2. Cascode amplifier [Sharma 2010] M. S. Ramaiah School of Advanced Studies 5
    6. 6. Cascode amplifierFigure 3. Cascode amplifier [Sharma 2010] M. S. Ramaiah School of Advanced Studies 6
    7. 7. Waveforms for Cascode amplifier for varying load Figure 4. Waveforms for change of output with respect to load M. S. Ramaiah School of Advanced Studies 7
    8. 8. Small signal modelFigure 5. Small signal model of cascode amplifier [Sharma 2010] M. S. Ramaiah School of Advanced Studies 8
    9. 9. Gain calculationFigure 6. Gain calculation [Sharma 2010] M. S. Ramaiah School of Advanced Studies 9
    10. 10. Cascode Current Mirror • This circuit does not need an external voltage bias. • The reference side of the mirror generates the bias voltages for both the transistors of the cascode output side. • However, this reduces the voltage range over which the output may swing.Figure 7. (a) Current mirror (b) Cascode current mirror (c) Simulation waveforms [Sharma 2010] M. S. Ramaiah School of Advanced Studies 10
    11. 11. Common-Source - Source-Follower Cascade RD M2 Rs M1 vO Cout vS IS1 CS IS2 RLD Figure 8. Common source and source follower cascode [Sharma 2010] M. S. Ramaiah School of Advanced Studies 11
    12. 12. Cascode Differential amplifier• Use of cascoding to increase load resistance• Cascode both the active loads and the differential pair – Higher effective load resistance – Higher ro for the differential pair – Reduces Miller effect M7 M8 M5 M6 vo Vbias M3 M4 M1 M2 vid I Figure 9. Cascode differential amplifier [Baker 2010] M. S. Ramaiah School of Advanced Studies 12
    13. 13. Summary• Best of both the circuit configurations (common source and common gate)• The cascode arrangement offers high gain, high stability and high input impedance• Wide applications as in current mirrors, modulators and differential OpAmp M. S. Ramaiah School of Advanced Studies 13
    14. 14. References• Dinesh Sharma (2010) CMOS Mixed Signal Design: OpAmp Design [online] available from < www.ee.iitb.ac.in/~smdp/DKStutorials/ opamp-tutorial.pdf > [01st July 2012]• Jacob Baker, R. (2010) CMOS: Circuit Design, Layout and Simulation. 3rd edn. Wiley-IEEE• Phillip E. Allen., and Douglas R, Holberg. (2002) CMOS Analog Circuit Design. 2nd edn. Oxford University Press M. S. Ramaiah School of Advanced Studies 14

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