Differential and Multistage Amplifiers

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# Differential and Multistage Amplifiers - PowerPoint PPT Presentation

Differential and Multistage Amplifiers. BJT &amp; FET Differential Pair Small Signal Model Biasing. Diff. BJT Amp. With Diff. Input. v B2 =0, v B2 =1 Operate the first transistor in the active region conducting I, Q 2 off. V B1. V B2 =0. Common Mode Input Voltage.

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## PowerPoint Slideshow about 'Differential and Multistage Amplifiers' - emily

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Presentation Transcript

### Differential and Multistage Amplifiers

BJT & FET Differential Pair

Small Signal Model

Biasing

March 08 2007

Diff. BJT Amp. With Diff. Input
• vB2=0, vB2=1
• Operate the first transistor in the active region conducting I, Q2 off

VB1

VB2=0

March 08 2007

Differential pair with small input
• For linear amplifier, apply small input,

March 08 2007

Large Signal Operation of BJT Diff. Amplifier
• Nonlinear response to change in voltage differential

March 08 2007

Transfer Characteristic of BJT Diff. Pair
• Linear only for small input!
• Difference is limited to less than VT/2

March 08 2007

Small Signal Model

March 08 2007

Simplified Model

March 08 2007

Differential FET Amplifier

Differential amplifier consists of two matched transistors which conduct the same current

March 08 2007

Exercises 7.1, 7.2

March 08 2007

Exercise 7.3
• V_DD and V_SS=1.5 V, k’_n(W/L)=4mA/V^2, V_t=0.5V, I=0.4mA, R_D=2.5k Ohm

March 08 2007

Diff. Amp. With Diff. Input
• vG2=0, vG1=vid

VG1

March 08 2007

Large Signal Operation of MOSFET Diff. Amplifier
• Nonlinear response to change in voltage differential

March 08 2007

Transfer Characteristic of FETDiff. Pair
• Linear only for small input!
• Difference is limited to V_ov

March 08 2007

Small Signal Analysis
• Input and output Impedances

March 08 2007

Simplified Model

Cut the differential pair into 2

March 08 2007

Mismatch of g_m

March 08 2007

Active load maintains bias current I

March 08 2007