Note: This page has been translated by MathWorks. Click here to see

To view all translated materials including this page, select Country from the country navigator on the bottom of this page.

To view all translated materials including this page, select Country from the country navigator on the bottom of this page.

Variable gain amplifier

Elements

The VGA block models a RF
Blockset™ variable
gain amplifier. The Simulink^{®} signal controls the non-linear gain.
The `VGA`

output voltage is a function of the input
voltage:

$${V}_{out}=g*{V}_{in}+{c}_{2}*{V}_{in}{}^{2}+{c}_{3}*{V}_{in}{}^{2}$$

**Coefficient Formulae**

Input Referred | Output Referred | |
---|---|---|

g | $$g=\frac{2\sqrt{G*{Z}_{out}*{Z}_{in}}}{\left|{Z}_{in}\right|}$$ | |

c_{2} | $${C}_{2}=\frac{g}{\sqrt{2*IP2*{Z}_{in}}}volt{s}^{-1}$$ | $${C}_{2}=\frac{{g}^{2}}{\sqrt{8*IP2*{Z}_{out}}}volt{s}^{-1}$$ |

c_{3} | $${C}_{3}=\frac{4}{3}.\frac{g}{2*IP3*{Z}_{in}}volt{s}^{-2}$$ | $${C}_{2}=\frac{4}{3}.\frac{{g}^{3}}{8*IP3*{Z}_{out}}volt{s}^{-2}$$ |

The three Simulink input ports are `Gain`

, `IP2`

(second-order
intercept point), and `IP3`

(third-order intercept
point). `In`

is the RF Blockset voltage input and `OUT`

is RF
Blockset voltage
output.

**Input impedance (Ohm)**Input impedance of the amplifier, specified as a scalar. The default value is

`50`

ohms.**Output impedance (Ohm)**Output impedance of the amplifier, specified as a scalar. The default value is

`50`

ohms.**Intercept points convention**Input-referred or output-referred convention for IP2 or IP3 intercept points, specified as

`Input`

or`Output`

.The default is

`Output`

.**Ground and hide negative terminals**Select this option to internally ground and hide the negative terminals. Clear the option to expose the negative terminals. By exposing these terminals, you can connect them to other parts of your model.

By default, this option is selected.

Was this topic helpful?