dB Conversion (DSP Blockset)

Convert magnitude data to decibels (dB or dBm).

Library

Description

The dB Conversion block converts a linearly scaled power or amplitude input to dB or dBm. The Input signal parameter specifies whether the input is a power signal or a voltage signal, and the Convert to parameter controls the scaling of the output. When selected, the Add eps to input to protect against "log(0) = -inf" parameter adds a value of eps to all power and voltage inputs. When this option is not enabled, zero-valued inputs produce -inf at the output. The size and frame status of the output are the same as the input.

Power Inputs

Select Power as the Input signal parameter when the input, u, is a real, nonnegative, power signal (units of watts). When the Convert to parameter is set to dB, the block performs the dB conversion

y = 10*log10(u)              % Equivalent MATLAB code

When the Convert to parameter is set to dBm, the block performs the dBm conversion

```
y = 10*log10(u) + 30
```

The dBm conversion is equivalent to performing the dB operation after converting the input to milliwatts.

Voltage Inputs

Select Amplitude as the Input signal parameter when the input, u, is a real voltage signal (units of volts). The block uses the scale factor specified in ohms by the Load resistance parameter, R, to convert the voltage input to units of power (watts) before converting to dB or dBm. When the Convert to parameter is set to dB, the block performs the dB conversion

```
y = 10*log10(abs(u)^2/R)
```

When the Convert to parameter is set to dBm, the block performs the dBm conversion

```
y = 10*log10(abs(u)^2/R) + 30
```

The dBm conversion is equivalent to performing the dB operation after converting the (abs(u)^2/R) result to milliwatts.

Dialog Box

Convert to: The logarithmic scaling to which the input is converted, dB or dBm. Tunable.
Input signal: The type of input signal, Power or Amplitude. Tunable.
Load resistance: The scale factor used to convert voltage inputs to units of power. Tunable.
Add eps to input to protect against "log(0) = -inf": When selected, adds eps to all input values (power or voltage). Tunable.

Supported Data Types

Double-precision floating point
Single-precision floating point

To learn how to convert to the above data types in MATLAB and Simulink, see Supported Data Types and How to Convert to Them.

See Also

dB Gain
DSP Blockset

Math Function
Simulink

log10
MATLAB

dB Gain	DSP Blockset
Math Function	Simulink
`log10`	MATLAB

Also see Math Operations for a list of all the blocks in the Math Operations library.

Cumulative Sum dB Gain