# dB Conversion

Convert magnitude data to decibels (dB or dBm)

## Library

Math Functions / Math Operations

`dspmathops`

## Description

The dB Conversion block converts a linearly scaled power or amplitude input to dB or dBm. The reference power is 1 Watt for conversions to dB and 1 mWatt for conversions to 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 output is the same size 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`. The reference power is 1 W for conversions to dB and 1 mW for conversions to dBm. Tunable.

Input signal

The type of input signal, `Power` or `Amplitude`.

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

 dB Gain DSP System Toolbox Math Function Simulink `log10` MATLAB