Band-Limited Op-Amp

Model band-limited operational amplifier

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Libraries:
Simscape / Electrical / Integrated Circuits

Description

The Band-Limited Op-Amp block models a band-limited operational amplifier. If the voltages at the positive and negative ports are Vp and Vm, respectively, the output voltage is:

$$V_{out}=\frac{A\left(V_p-V_m\right)}{\frac{s}{2\pi f}+1}-I_{out}*R_{out}$$

where:

• A is the gain.

• R_out is the output resistance.

• I_out is the output current.

• s is the Laplace operator.

• f is the 3-dB bandwidth.

The input current is:

$$\frac{V_p-V_m}{R_{in}}$$

where R_in is the input resistance.

The block does not use the initial condition you specify using the Initial output voltage, V0 parameter if you select the Start simulation from steady state check box in the Simscape™Solver Configuration block.

Examples

Model Operational Amplifier with Noise

Incorporate noise into an electrical simulation. The circuit models an amplifier with a high-frequency roll off frequency of 10MHz. The Band-Limited Op-Amp block adds the noise. The Voltage Source block, Vn, specifies an equivalent voltage noise density of 20 nV/Hz^0.5. You can also add the thermal noise from the resistors R1 and R2 by setting the Noise mode parameter of the two Resistor blocks to Enabled. However, running this model with different combinations of noise sources shows that the main source of noise is the equivalent noise voltage.

• Open Model

Ports

Conserving

+ — Non-inverting input

electrical

Electrical conserving port associated with the op-amp non-inverting input

- — Inverting input

electrical

Electrical conserving port associated with the op-amp inverting input

OUT — Output voltage

electrical

Electrical conserving port associated with the op-amp output voltage

Parameters

Gain, A — Open-loop gain

1000 (default)

The open-loop gain of the operational amplifier.

Input resistance, Rin — Input resistance

1e6 Ohm (default)

The resistance at the input of the operational amplifier that the block uses to calculate the input current.

Output resistance, Rout — Output resistance

100 Ohm (default)

The resistance at the output of the operational amplifier that the block uses to calculate the drop in output voltage due to the output current.

Minimum output, Vmin — Minimum output

-15 V (default)

The lower limit on the operational amplifier no-load output voltage.

Maximum output, Vmax — Maximum output

15 V (default)

The upper limit on the operational amplifier no-load output voltage.

Maximum slew rate, Vdot — Maximum slew rate

1000 V/s (default)

The maximum positive or negative rate of change of output voltage magnitude.

Bandwidth, f — Open-loop bandwidth

1e5 Hz (default)

The open-loop bandwidth, that is, the frequency at which the gain drops by 3 dB compared to the low-frequency gain, A.

Initial output voltage, V0 — Initial output voltage

0 V (default)

The output voltage at the start of the simulation when the output current is zero.

Note

This parameter value does not account for the voltage drop across the output resistor.

Extended Capabilities

C/C++ Code Generation
Generate C and C++ code using Simulink® Coder™.

Version History

Introduced in R2008a