![]() ![]() Often, the absolute bandwidth requirement for the suboctave filter becomes narrower as the center frequency reduces. A suboctave filter removes these interfering signals before they can hit a nonlinear component in the signal chain (such as an amplifier or mixer). This occurs when two out-of-band (OOB) spurs add or subtract and create a spur that falls in band, potentially masking a desired signal. The preselector suboctave filtering needs to be near the beginning of the signal chain and is used to address second-order intermodulation distortion (IMD2) spurs that can show up in the presence of interferer signals (also known as blockers). (a) An image band and (b) an IF band must be rejected before the mixer. (a) Suboctave preselection mitigates IMD2 issues (b) filter bands become wider as frequency increases. The filtering functions in this block diagram can be divided into four main categories:įigure 1. There is a series of amplification, filtering, and attenuation control (the RF front end) before the frequencies are converted to an IF signal that the ADC can digitize. The antenna receives a broad spectrum of frequencies. The basic theory of operation of this signal chain is the following. RF Signal Chain OverviewĪ typical wideband signal chain covering 2 GHz to 18 GHz is shown in Figure 1. the latest product solutions, it becomes clear how system designers can easily achieve their goals. Then, by comparing these traditional technologies vs. ![]() Further, a review of traditional technologies can give insight into the status quo. To start this exploration, a general overview of RF signal chains and definitions can assist in explaining where and why filters are needed. In general, this trend means a relaxation of rejection requirements for filters, which opens them up to further size and tunability optimization. With a higher ADC input frequency, the constraints placed on filters in the signal chain have changed. As filters have traditionally consumed large amounts of area, they are an obvious area to explore size reduction.Īt the same time, receiver architectures are evolving with the ability for analog-to-digital converters (ADCs) to sample at higher input frequencies. With the goal to continuously reduce size, weight, power, and cost, while increasing or maintaining performance, it has become necessary for RF system designers to evaluate each component in the signal chain and look for opportunities to innovate. This article will explore filters within RF signal chains, discuss the concept of blocker signals, review traditional filtering technologies, and conclude with the latest product solutions for optimizing signal chain performance. Filters have played an essential role in reducing these unwanted signals, particularly in the receiver RF front end and local oscillator (LO) portions of these systems. In today’s multichannel, wideband multioctave tuning RF receivers, it is often necessary to eliminate unwanted blockers to preserve the fidelity of signals of interest. How Digitally Tunable Filters Enable Wideband Receiver Applications
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