dB Conversion

Convert magnitude data to decibels (dB or dBm)

• 

Libraries:
DSP System Toolbox / Math Functions / Math Operations
Communications Toolbox / Utility Blocks

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 block's 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 parameter is not selected, zero-valued inputs produce -Inf at the output.

Examples

Parametric Audio Equalizer

Model an algorithm specification for a three band parametric equalizer

• Open Model

Ports

Input

Port_1 — Input signal

scalar | vector | matrix

Input signal to be converted, specified as a real scalar, vector, or matrix.

When the Input signal parameter is set to:

• Power — The input is treated as a power signal, specified in Watts.

• Amplitude — The input is treated as a voltage signal, specified in Volts.

Data Types: single | double

Output

Port_1 — Output signal

scalar | vector | matrix

The converted output signal, returned as a scalar, vector, or matrix. The output is the same size, and data type as the input. The output y is calculated as follows.

When the Input signal parameter is set to Power and Convert to parameter is set to:

• dB — The block performs this dB conversion:

  y = 10*log10(u)	
  

• dBm — The block performs this dBm conversion:

  y = 10*log10(u) + 30
  

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

Input u is a real, nonnegative, power signal, specified in Watts.

When the Input signal parameter is set to Amplitude and Convert to parameter is set to:

• dB — The block performs this dB conversion:

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

• dBm — The block performs the following dBm conversion:

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

Input u is a real voltage signal, specified in Volts.

The dBm conversion is equivalent to performing the dB operation after converting the (abs(u)^2/R) result to milliwatts. The scale factor, R, is specified in Ohms.

Data Types: single | double

Parameters

Convert to — Signal to convert

dB (default) | dBm

The logarithmic scaling to which the input is converted, dB or dBm. The reference power is 1 Watt for conversions to dB and 1 mW for conversions to dBm.

Amplitude conversions use 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 Input signal parameter is set to Power and Convert to parameter is set to:

• dB — The block performs this dB conversion:

  y = 10*log10(u)	
  

• dBm — The block performs this dBm conversion:

  y = 10*log10(u) + 30
  

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

Input u is a real, nonnegative, power signal, specified in Watts.

Input signal is set to Amplitude and Convert to parameter is set to:

• dB — The block performs this dB conversion:

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

• dBm — The block performs this 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 mW. The scale factor R is specified in Ohms.

Input u is a real voltage signal, specified in Volts.

Tunable: Yes

Input signal — Type of signal

Amplitude (default) | Power

The type of input signal, Power or Amplitude.

When Input signal is set to:

• Power –– Input u is a real, nonnegative, power signal (units of Watts).

• Amplitude –– Input u is a real voltage signal (units of Volts).

Load resistance (ohms) — Scale factor

1 (default) | positive scalar | positive integer

The scale factor R, specified in ohms. The block uses the scale factor to convert voltage input to units of power (watts) before converting to dB or dBm.

Tunable: Yes

Dependencies

To enable this parameter, set the Input signal parameter to Amplitude.

Data Types: single | double | int8 | int16 | int32 | uint8 | uint16 | uint32 | Boolean | fixed point
Complex Number Support: Yes

Add eps to input to protect against "log(0) = -inf" — Add eps

off (default) | on

Select this parameter to add eps to all input values (power or voltage).

Tunable: Yes

Block Characteristics

Data Types	double | single
Direct Feedthrough	no
Multidimensional Signals	no
Variable-Size Signals	no
Zero-Crossing Detection	no

Extended Capabilities

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

Version History

Introduced before R2006a