What Is an Envelope Detector?

A simple electronic circuit that grabs a high-frequency signal as an input, corrects it and releases the new signal as an envelope for the original signal is known as an envelope detector. Diode detectors and precision rectifiers are often combined to improve performance. Common applications include audio equipment such as electronic instruments and portable radios. Simplicity and efficiency are perhaps the most significant advantages of an envelope detector. Several disadvantages to using these devices are often outweighed by the benefits.

A high-frequency input taken in by an envelope detector typically passes through a few components before it is released as an envelope. Essentially, the rising edge of a signal is stored in a capacitor. As the input signal diminishes, the energy stored in the capacitor flows through a resistor as the new signal output. In most envelope detectors, a diode also is part of the circuit and this diode typically rectifies the signal, creating the enveloped output.

Diode detectors typically have all the necessary parts to receive and envelope a signal, producing the desired output. To clean up the envelope, however, a precision rectifier is often added to a diode detector. This can filter out other input signals, leaving only the desired input to translate into a better output.

Many of the applications for an envelope detector are related to audio equipment. For instance, many electronic music instruments such as electric guitar or bass might use some form of an envelope detector to change the sound. Additionally, portable radios almost always contain a simple envelope detector that can receive and translate radio signals into sounds.

Several advantages have made envelope detectors useful in many applications. Perhaps most importantly, an envelope detector is often considered simple because it contains only a few elements that can produce the desired effects. This simplicity typically means the cost of an envelope detector also is low. Once configured to a specific task, most envelope detectors are reliable and accurate, as well.

Disadvantages to using an envelope detector are typically associated with the possibility of distortion. For instance, most radios have less than perfect sound quality because of inconsistent input signals that create inconsistent or low-quality envelopes. Additionally, many of these detectors are susceptible to noise from other types of transmissions and the input must be filtered to compensate. Many of these disadvantages are acceptable, however, because of the value of envelope detectors, in general.