VCC VDD

R M2 E2 M3 M4 M5

Q2 Q3 Q1 Q4 M1

RB

VEE Multiple PNP current sources; IC3 and Multiple P-channel sources: M1 is a IC4 are matched to IC1 (the control tran- long, narrow device that sets the current sistor) but IC2 is reduced by RE2 . The level. Usually M3, M4, and M5 have Q2 – RE2 combination is a Widlar cur- the same lengths but may differ in width rent source. to set different output current values.

VCC VDD

Current Mirror

In Out In Out

iM = iD1 iM = iC1 iC1 – iC2 iD1 iD1 – iD2 iC1

iD2 iC2 M1 M2 Q1 Q2 vIN1 vIN2 v IN1 vIN2

VEE VSS Concept of using a current mirror circuit Current mirror with N-channel MOSFET to allow subtraction of collector currents differential pair. at a simple node by KCL.

VCC

iOUT RBIAS

Q1 iOUT Q2 iIN

Q1 Q2 RE

VEE VEE

Widlar , for which The most basic current mirror with hi kT ⎛⎞IC1 FE IN I = ln . The collector cur- iOUT = and an output resistance C 2 ⎜⎟ h + 2 qREC⎝⎠I 2 FE rent of Q2 may be much lower than Q1 VVCE + A equal to rO2 = . with only a modest value for RE. IC

VCC iIN i iIN OUT iOUT

Q3 Q3

Q1 Q2 Q1 Q2

VEE VEE

Current mirror using a stage to balance input and output. Output Wilson current mirror –this has a much impedance is still rO2. The minimum higher output resistance from the output is very low – VCESAT of cascoding effect of Q3. Q2.

iIN i OUT

Q3 Q4

iIN iOUT

Q1 Q2 M1 M2

VEE VSS

Wilson current mirror with an additional , Q3, to equalize the collector- The primitive current mirror in MOS emitter of the matched pair Q1- devices. Because usually Q2. have lower output resistances than BJTs, this circuit often causes lower gains than its BJT counterpart.

iIN iOUT iIN iOUT M3 M4 V BIAS M4 M3

M1 M2 M1 M2

VSS VSS A Wilson current mirror in MOS devices with a fourth transistor, M3, to equalize A cascoded current mirror with M3 and the drain-source voltages of the matched M4 as the cascoding . With pair M1 – M2. Because of the relatively careful selection of VBIAS this circuit can high value of VTH, this circuit, which have an output resistance that is much requires a minimum of higher than the uncascoded version and still operate with input to V drops of 2(VTH +VOV ) across the left and SS only VVTH + OV . VTH + 2VOV on the right, may not be satis- factory for low voltage systems.

VCC VDD

Q3 Q4 M3 M4 (control) (control)

iM = iD1 iM = iC1 iC1 – iC2 iD1 iD1 – iD2 iC1

iD2 iC2 M1 M2 Q1 Q2 vIN1 vIN2 v IN1 vIN2

VEE VSS

Simplest bipolar current mirror within a Simplest CMOS MOSFET current mir- differential . Q3 is the control ror within a . M3 is transistor for the current source Q4. Be- the control transistor for the current cause Q3 is connected as a , it has a source M4. Because M3 has its drain low impedance to the . Q4 and gate connected, it has a low imped-

is open collector and so exhibits a rela- ance to the power supply ( ZM 33= 1/ gm ). tively high , that is, it M4 has an open drain and so exhibits a approximates a constant current source. relatively high output impedance, that is, it too approximates a constant current source.

Constant Current Sources (Biasing)

Complementary I sense Differential Pair Symmetry Inp uts Input Stage Output (2 – PNP transistors) Compensation Stage Capacitor Output

Current Mirror -A (Diff to single-ended Protection conversion)

Block Diagram of a Bipolar

The tables show the quiescent conditions for the transistors in the bipolar operational am- plifier that I use in class. The assumptions about the devices are:

Device Type VBE hFE = β VA VCESAT NPN 0.6 volts 100 150 volts 0.2 volts PNP 0.6 70 30 0.3

Quiescent Currents and Transistor Model Parameters Transistor IC IB re ro gm = IC/kt/q Q7 227 ua. 2.27 ua. 113 ohm 704 kohm 8790 usie. Q8 14.2 0.142 1.8 K 12.4 Meg. 549 usie. Q9 227 3.35 113 132 K 8720 Q10 227 2.3 113 174 K 8720 Q11 30 0.43 860 1.3 Meg. 1150 Q12, Q13 15 0.21 1.72 K 2.7 Meg. 573 Q14, Q15 15 0.15 1.72 K 10.7 Meg. 576 Q16 12.3 0.12 2.1 K 14.2 Meg. 477

VCC

RE 1.8 KΩ IC11 = 30 µA. Q2 Q9 Q11 Q10 Q5 Q1

50 K Q12 Q13 35 Ω Invert Non-invert D1 vOUT D2

35 Ω D3

CCOMP = 15 pf.

100 K Q4 Q16 Q3 Q8

Q14 Q15 50 K

Q7 Q6 50 K 50 K 35 Ω 500 Ω 500 Ω

VEE