Characteristics and Testing of Operational Amplifiers: Op-Amp Properties and Applications, Lecture notes of Design

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Mixed/analog-signal testing.

Analog Circuit Testing

-^ Test Problems •^ Basic Components / Parameters •^ Test Methods^ −^ DSP Based^ −^ Design for Test^ −^ Built-in Self-Test^ −^ Algorithmic Method

Mixed/analog-signal testing.

-^ Continuous signals in analog circuits •^ Fault models •^ Device parameters •^ Test time •^ Test effectiveness (fault coverage) •^ Test cost

Test Problems

Mixed/analog-signal testing.

Operational Amplifiers

^

Ideal op-amp

1.voltage-controlled voltage source2.infinite voltage gain3.infinite input impedance4.zero output impedance5.infinite bandwidth6.no offset voltage7.infinite CMRR


Va Vb

A(V^ -Va^

)b

i^ =0a i =0b

Property

Mixed/analog-signal testing.

1.finite gain(practical op-amps A

2.finite linear range(V

>VDD^

>GND)o

3.offset voltage^ − input offset voltage V

is defined as theoffset^

differential

input voltage needed to restore V

=0o^

−^ for MOS op-amps, V

is about 5~15mvoffset

for BJT op-amps, V

is about 1~2mvoffset^

Property of real op-amp

Mixed/analog-signal testing.

5.Frequency Response^ −

Limited bandwidth(typically, 100MHz unity-gainbandwidth) − Gain decreases at high frequencies , becausea.stray capacitancesb.finite carrier mobilities 6.Slew Rate(typically,for MOS op-amps,1~50V/

μμμμ s)

−^ The maximum rate of output change dV

/dto^

7.Nonzero Output Resistance^ −

Typically,0.1~5k

Property of real op-amp(con’t) − Large Ro will limit frequency response when acapacitor is connected to its output

Very high(A=10 Mixed/analog-signal testing.

Dominant pole (100MHz unity-gainbandwidth)High(60~80dB)High(>100M

Low(0.1~5k

Low(<0.

μA) Low(<10mV,<0.2nA) InfiniteInfinite InfiniteInfiniteZeroZeroZero

Open-loop gainOpen-loop bandwidthCommon-mode rejectionratioInput resistanceOutput resistanceInput current

Practical(typical) ideal

property

Characteristics of Op-Amps

Mixed/analog-signal testing.

Second block provides:^ −

level shift − added gain − differential-to-single-ended conversion

Output stage provides:^ −

low output impedance − large driving capability

Operational-amplifier architectures(con’t)

Mixed/analog-signal testing.

741 OPAMP (BJT)

Bias network

Differential amplifier

CC-CE gain stage

Level shift

Output stage

Mixed/analog-signal testing.

Active-RC Integrator

^

-^

v^ (t)I^

v^ (to )

0 0V

i^1

i^1 C

R

^
^

^ 

Miller or inverting integrator

Mixed/analog-signal testing.

Frequency response of the integrator

-6dB/octave

ω(log scale)

dB



^
^0

Mixed/analog-signal testing.

Switched-capacitor Integrator(con’t)


c^1

c^2

v^ i

c^1

c^2

During

φ^1

During

φ^2

−R^ eq

= T/C c^

2 −Time constant=C

R^1 eq

= (T c

C^ )/C 1

2

Mixed/analog-signal testing.

Switched-capacitor Integrator(con’t) ϕ^1


ϕ^2

c^1

c^2

c^ s

Advantage: −Time constant=(T

C^ )/Cc 1

can be 2

well controlled in an IC process(The accuracy of capacitor ratiosIn MOS technology can becontrolled to within 0.

Disadvantage: −^ it is sensitive to stray capacitances

Mixed/analog-signal testing.

A/D Converters

-^ Successive approximation •^ Integrating •^ Flash •^ Sigma-delta

Mixed/analog-signal testing.

Successive Approximation(I)^ •^

Reasonably quick conversiontime • Moderate circuit complexity • Basic ideal: Binary search todetermine the closest digitalword • Signed Input: within • Output: offset-binary coding Ex : 2bit offset-binary code

Start

(^1) , 0 /^

== i VV , ADin Sample

V^ ADin V^ > / (^1) = b i

(^0) = bi −→ +
 ^





 ^ ++
^ →^ 
 

(^1) +→ ii  ≥ Stop Yes

NO Yes

NO

Number code

11 (^1001) 00

1 (^0) -