Presentation on theme: "Differential Amplifiers"— Presentation transcript:
1 Differential Amplifiers Why differential?• Well suited for integrated circuit (IC) fabrication• Less sensitive to noise• Possibility to couple amplifier stages without capacitorssedr42021_0701.jpgFigure 7.1 The basic MOS differential-pair configuration.
2 Operation with a Common-Mode Input Voltage sedr42021_0702.jpgFigure 7.2 The MOS differential pair with a common-mode input voltage vCM.
3 Operation with a Differential Input Voltage sedr42021_0704.jpgFigure 7.4 The MOS differential pair with a differential input signal vid applied. With vid positive: vGS1 > vGS2, iD1 > iD2, and vD1 < vD2; thus (vD2 - vD1) will be positive. With vid negative: vGS1 < vGS2, iD1 < iD2, and vD1 > vD2; thus (vD2 - vD1) will be negative.
4 Large-Signal Operation sedr42021_0705.jpgFigure 7.5 The MOSFET differential pair for the purpose of deriving the transfer characteristics, iD1 and iD2 versus vid = vG1 – vG2.
5 sedr42021_0706.jpgFigure 7.6 Normalized plots of the currents in a MOSFET differential pair. Note that VOV is the overdrive voltage at which Q1 and Q2 operate when conducting drain currents equal to I/2.
6 sedr42021_0707.jpgFigure 7.7 The linear range of operation of the MOS differential pair can be extended by operating the transistor at a higher value of VOV.
7 Small-Signal Operation of The MOS Differential Pair Differential Gainsedr42021_0708a.jpgFigure 7.8 Small-signal analysis of the MOS differential amplifier: (a) The circuit with a common-mode voltage applied to set the dc bias voltage at the gates and with vid applied in a complementary (or balanced) manner. (b) The circuit prepared for small-signal analysis.
8 Common-Mode Gain and Common-Mode Rejection Ratio sedr42021_0710a.jpgFigure (a) The MOS differential amplifier with a common-mode input signal vicm. (b) Equivalent circuit for determining the common-mode gain (with ro ignored). Each half of the circuit is known as the “common-mode half-circuit.”
9 The BJT Differential Pair sedr42021_0712.jpgFigure The basic BJT differential-pair configuration.
10 sedr42021_0714.jpgFigure Transfer characteristics of the BJT differential pair of Fig assuming a . 1.