The Limits of Limiting Amplifiers
Is many applications, amplifiers are used to increase the strength of a signal, while minimizing the distortion and noise without sacrificing efficiency. However, with most receiver systems, and other applications, achieving the highest signal power isn’t the goal. As receivers circuits are typically highly sensitive to input power, and can be desensitized or damaged if exposed to sustained signal energy that exceeds some nominal amount depending on the specs of the receiver, capping the maximum amount of signal power over a frequency range can be a desired function. This is where limiting amplifiers are used.
Unlike many amplifiers that have a maximum output power limited by the input signal, gain, design feature, bias, and available power, limiting amplifiers are equipped with circuitry that provides a hard maximum power limit at the output. Hence, over a given frequency range, a limiting amplifiers will only output a set maximum signal energy, independent of the input. Like other amplifiers, the dynamic range, gain, and gain flatness are still priority parameters of limiting amplifiers.
As limiting amplifiers are often used in applications that require high signal fidelity, such as sensitive radar receivers, fiber optic transceivers in RF/optic converters, linearity, noise, and additive phase noise performance are also considerations. For high throughput data signals, like those used with fiber optic, microwave backhaul, and 5G millimeter-wave trails, maintaining signal quality while limiting input power to highly sensitive receiver circuits often jeopardized by interference, is key. Electronic Warfare (EW) applications are another common use of limiting amplifiers where sensitive radar receivers, active electronically steered array (AESA) transmit/receiver (TR) modules, and critical communication receivers are subject to high signal energies from nearby friendly transmitters and unfriendly jamming or interference.
Another key benefit of limiting amplifiers is to present low variation input power to a receiver circuit. This function can also be used to remove AM modulation from incoming signals and act as a comparator. These features make limiting amplifiers critical in the use of instantaneous frequency measurement (IFM) receivers, directional finding, digital radio frequency memory (DRFM), and a range of signal intelligence (SIGINT) uses.
Limiting amplifiers can be realized in a variety of ways. Some of the simplest output limiting amplifiers use clamping networks, which can be as simple as a two Schottky diode circuit and current limiting resistor, or as complex as a multi-transistor, diode, and resistor network for greater precision and faster recovery. Other types of limiting amplifiers operate using successive gain stages that “compress” from the input to the output of the amplifier. With any type of limiting amplifier, design challenges include wideband power limiting, as it is desirable for many applications for limiting amplifiers to cover multiple frequency octaves, especially with EW applications. Other design considerations must account for low variation power limiting, frequency equalization/stability, thermal management/compensation, harmonics, and dynamic range. Due to the often extreme operation temperatures and harsh environments that limiting amplifiers operate, they are commonly assembled in hermetically sealed packages with rugged connectors and wide operational temperature ranges.
To learn more about Pasternack’s line of Limiting Amplifiers, visit this link https://www.pasternack.com/limiting-amplifiers-category.aspx