RF detectors are essential components in communication systems and measuring instruments, playing a crucial role in signal monitoring and power control. This article provides an overview of common types of RF detectors and their typical applications.
RF detectors can generally be categorized into several main types. One of the most widely used is the Log Amp (Logarithmic Amplifier), which operates by cascading multiple stages of gain and using transconductance amplifiers to sum the resulting currents. The architecture of a log amp allows for an extremely wide dynamic range. For instance, devices like the HMC602 and AD8318 support frequency ranges from 1 MHz to 8 GHz with a dynamic range of up to 70 dB, making them suitable for most communication system requirements.
Another common type is the RMS detector, which uses a squaring circuit to measure the power level of the input signal. Unlike logarithmic detectors, RMS detectors provide accurate power readings regardless of whether the input signal is a single tone, wideband, or modulated. A typical block diagram of an RMS detector is shown below.
In addition to detecting power levels, many RF detectors also allow for the use of an external voltage to set a constant power output via a variable gain amplifier (VGA). This feature is useful in applications requiring precise power control. An example of such a configuration is illustrated below.
The third category includes peak and envelope detectors, which are designed to capture the peak and envelope of the input signal. These detectors operate similarly to filters, where the envelope of a wideband signal is extracted using a low-pass filter. Therefore, selecting the appropriate bandwidth is critical depending on the application. Peak detectors are commonly used in power amplifiers and receiver protection circuits to prevent damage from excessive signals. They are also used in radiology machines for calibrating parameters such as LOL and SSB by analyzing the envelope of the output signal.
Moreover, certain RF detectors can be used to assess the matching characteristics of an RF port based on the Voltage Standing Wave Ratio (VSWR).
Lastly, the SDLVA (Successive Detector Log Video Amplifier) is frequently used in military applications. A key advantage of this type of logarithmic detector is its excellent frequency response flatness, making it ideal for high-precision measurements.
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