Review
of BJT and MOSFET Differential Amplifiers and Frequency Response
2016. 12. 26
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npn BJT: I S = 210 ‐15 A, V A = 50 V, = 200. C =40pF C =4pF pnp BJT: I S = 110 ‐15 A, V A = 40 V, = 100. C =36pF C =4pF
nMOSFET: μ n C ox = 200 μA/V 2 , V TH = 0.4 V, and λ = 0.1V -1 .
pMOSFET: μ p C ox = 100 μA/V 2 , V TH =- 0.4 V, and λ = 0.1V -1 .
1. Draw a circuit model for a voltage amplifier with an open‐circuit voltage gain of 5, an input impedance of 2k with an input capacitance of 30 pF, and an output impedance of 5 k. A signal source with an output impedance of 0.5 k and a 20 k load are connected to the amplifier through a 47F capacitor respectively . Calculate the midrange gain, low‐frequency and high frequency 3‐dB points.
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npn BJT: I S = 210 ‐15 A, V A = 50 V, = 200. C =40pF C =4pF pnp BJT: I S = 110 ‐15 A, V A = 40 V, = 100. C =36pF C =4pF
2.(a)Design a 10-mA current sink with a BJT current mirror. The device parameters of npn BJT are: V A = 50V, = 100. This current mirror is to operate between +5 V and -5 V voltage sources. Plot the circuit diagram of your design and also give its equivalent Norton model, which should include the output resistance.
(b) Design a two-LED blinker circuit. You can use a BJT differential pair with a 10 mA current sink designed in Part(a). A differential signal switching between +1V and -1V controls the LEDs and make them turn on
alternately. The turn-on current of LED should be 10 mA, and the turn-on voltage is 1.5V. This circuit is to operate between +5 V and -5 V voltage sources.
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3. Design a differential amplifier with npn BJT transistors, and ±5V DC sources. Assume we have already a 2‐mA current sink with a 100 k output resistance (you don’t need to design this current source). The negative output will be used to feed an amplifier with a very high input impedance. The voltage gain for this single‐ended output amplifier should be ‐40. Complete the design and estimate the input impedance for both differential‐mode and common‐mode input signals, output impedance, common‐
mode gain, and CMRR (for single‐ended output). Also calculate the DC level at the output point (which decides the high‐voltage limit of input common mode).
4 Find the input common mode range if
the current source is a simple current mirror and V SAT =0.3V for BJTs.
PRACTICE!!!
4.(a)如圖之放大器，要求電晶體的 I C 為2mA，電壓增益( o / s )大約為-40。此外， R L =2k、 R s
=600、 V CC =9V。 [Note:建議先由 g m 、 R L 估算 R C ；但要考慮輸入的負載效應~ Rp//r /( R s +Rp// r )。
估算 V C ，選擇一個足夠大的 V CE ，給定 V E ，再由 V C 估算 R E 。]
(b)我們希望此放大器的低頻3dB點大約在50Hz，設計適當的 C C1 、 C C2 和 C E 。(使用相同電容值) (c)估算此放大器的高頻3dB頻率。(畫出高頻小訊號模型，並使用Miller＇s approx.)
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5. Design a set of current sources for a BJT circuit which needs 0.4 mA and 0.8 mA current sinks, and 2 mA source. Plot the Norton model for each current source. Use +5 and ‐5 V DC power supplies.
npn BJT: I S = 210 ‐15 A, V A = 50 V, = 200.
pnp BJT: I S = 110 ‐15 A, V A = 40 V, = 100. 7
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250 200
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6. A common‐gate amplifier has parameters shown below the
circuit diagram.
(a) Plot the high‐frequency small signal model. (Regroup the capacitors in parallel for analysis.)
(b) Calculate the midrange gain.
(c) Estimate the high‐frequency 3dB point.
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7. For each of the differential amplifier module, plot the half circuit for the differential‐mode signal input and calculate the differential gain for double‐ended output.
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(a)
(b)
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