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# OpAmp (Operational Amplifier)

## OpAmp (Operational Amplifier)

##### Parameters

Name

Description

Units

Default

Gain

Open loop DC gain of amplifier

dB

100

CMR

Common mode rejection ratio

dB

None

Rout

Output resistance

Ohm

100

RDiff

Differential input resistance

MOhm

1

CDiff

Differential input capacitance

F

0

RCom

Common mode input resistance

MOhm

1

CCom

Common mode input capacitance

F

0

SlewRate

Signal slew rate

V/sec

1e+6

IOS

Input offset current

A

0

VOS

Input offset voltage

V

0

BW

Gain bandwidth product (unity gain bandwidth)

MHz

1

Pole1

Dominant pole frequency (overides BW parameter)

Pole2

Pole3

Pole4

Pole5

Zero1

Feed forward zero frequency

Inoise

Input spectral noise current

A/sqrt(Hz)

0

Vnoise

Input spectral noise voltage

V/sqrt(Hz)

0

VEE

Negative supply voltage

V

15

VCC

Positive supply voltage

V

15

DeltaVEE

Delta difference between saturated voltage and negative supply voltage (see note 4)

V

0.3

DeltaVCC

Delta difference between saturated voltage and positive supply voltage (see note 4)

V

0.3

RDiff > 0
CDiff > 0
RCom > 0
CCom > 0
by default:
CMR = ∞
Pole2 = ∞
Pole3 = ∞
Pole4 = ∞
Pole5 = ∞
Zero1 = ∞

##### Notes/Equations
1. The BW parameter is the GainBandwidth product, i.e. it is the frequency at which the gain is unity or 0 dB. Pole1 is the basic amplifier pole and corresponds to the frequency where the gain starts sloping downward.
BW and Pole1 can be specified simultaneously; however, if both are entered, Pole1 will override BW, and Pole1 must then be entered as BW/Gain. The Gain parameter is the open loop gain of the opamp and it must be converted out of dB only for use in setting Pole1, i.e., Gain=10Gain_dB/20.
2. To match the phase shift from the data sheet, adjust the values of Pole2 through Pole5.
3. Zero1 is used for operational amplifiers with feed-forward or lead-lag compensation networks.
4. Output voltage is generally less than the rail voltage (VCC and VEE). Use DeltaVCC and DeltaVEE to specify the difference between the rail voltage and actual output voltage. For example, if VCC is +5V and the positive output is +4.5V, set DeltaVCC to 0.5V.
5. This opamp is a nonlinear model. If your circuit cannot achieve convergence using this model, use the OpAmpIdeal linear model.
6. The relationship between input and output voltages is given in the equation:
Im × tanh(Vin/Im)=Vout/A0 - 10 × (Vclip-Vout) + d/dt (Vout × Tau1/A0)
where
A0 is open loop DC gain
Vclip = Vout as long as it is not limiting
Im = SlewRate × Tau1/A0
Tau1=A0/2/π/BW when Pole1=0, otherwise Tau1=1/2/π/BW
7. In releases before ADS 2008, the OpAmp component contributed noise from the following noise contributors: AMP1.SRC1 and AMP1.SRC2. Starting with ADS 2008, only one noise contributor, called AMP1, is published.
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