Announcements Lab 9 reports due now EE105 Fall 2005 Check your homework lab grades next week Microelectronic Devices and Circuits Reading Chapter 9 6 10 7 2 Final December 20 12 30 3 30pm Bechtel Aud Sibley Lecture 29 BJT Biasing Summary 2 Lecture Material PNP Transistor Last lecture BJT amplifiers common emitter common collector common base Emitter P VEB Base N IB This lecture Collector P BJT biasing Example amplifier Review IE VEC IC 3 4 Cutting Through the Complexity Multi Stage Voltage Amplifier Two Approaches 1 Eliminate background transistors to reduce clutter 2 Identify the signal path between the input and output 5 6 1 What s Left First Approach Find I V Sources Voltage at base of Q2 is set by totem pole 7 8 Identifying the Stages Second Approach Find Signal Path First stage or two stages CS CB cascode Second stage or two stages CD CC voltage buffer Why does this make sense for a voltage amplifier 9 Find Key Two Port Parameters 10 Two Port Parameters Cont Output resistance of cascode Rout CS CB roc ro 2 1 g m 2 r 2 RS 2 roc Rup ro 6 1 g m 6RS 6 11 12 2 Output Swing VOUT MIN Output Resistance and Voltage Gain Minimum output voltage M10 M3 and Q2 are suspects Source resistance of the CC stage is the output resistance of the CD stage small Rout Rout CC 1 gm 4 RS CC o M10 goes into triode when VOUT 0 5 V 1 1 1 g m 4 g m 3 o g m 4 M3 goes into triode when VSD3 0 5 V VOUT 0 5 V 0 7 V 0 2 V Open circuit voltage gain Av last two stages have nearly unity gain Q2 goes into saturation when VCE2 0 1 V or VBC2 0 6 V VOUT VB2 VBC2 VSG3 VBE4 2 V 0 6 V 1 5 V 0 7 V VOUT 2 2 V Av g m1 o ro 2 ro 6 1 g m 6ro 7 13 14 Insight into the Frequency Response Output Swing VOUT MAX Maximum output voltage Q4 M5 and M6 are suspects Q4 goes into saturation when VCE4 0 1 V VOUT 4 9 V M5 goes triode when VSD5 0 5 V VOUT 3 8 V M6 goes triode when VSD6 0 5 V VOUT VS6 0 5 V VSG3 VBE4 3 5 0 5 1 5 0 7 V 3 8 V 15 Qualitative Insight 16 Node X Could always do brute force open circuit time constants High impedance node is node X look at RTxCx Capacitance Cx Cgd6 C 2 Cgd3 CM3 CS CB is a wideband stage so is the CD CC buffer Miller for CD stage M3 Look for large RTxCx products high impedance nodes are likely candidates 17 18 3 Finding the Miller Capacitance CM3 Dominant Pole of Voltage Amplifier Cgs3 Th venin resistance for CX RTx Rout 2 R in 3 Rout CB R in CD X CD RL3 RTx roc ro 2 1 g m 2 r 2 RS 2 ro 6 1 g m 6ro 7 ro 2 o R L3 Gain across Cgs3 AvCgs 3 1 g m 3 R L 3 Dominant pole 1 1 RTx C x RL3 Rin4 19 EECS 105 in the Grand Scheme 20 EECS 105 in the Grand Scheme Example Cell Phone 21 22 4
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