RF noise suppression using anechoic chamber test circuit - News - Global IC Trade Starts Here Free Join
The ever-growing prevalence of GSM handsets has led to an increasing number of unwanted RF signals, which can distort the performance of electronic circuits unless the circuits are sufficiently shielded against RF interference. Ensuring reliable operation of electronic devices requires rigorous testing of their RF suppression capabilities, making this a critical aspect of modern product development. This article outlines a general RF suppression measurement technique using an RF anechoic chamber, explaining its components and operational modes while providing examples of actual test results. Most contemporary cell phones utilize Time Division Multiple Access (TDMA) technology, which employs high-frequency carriers modulated by on/off pulses at a frequency of 217 Hz. Components within a circuit that are sensitive to RF interference can demodulate these carrier signals, generating a 217 Hz tone along with its harmonics. Since many of these frequencies fall within the audio spectrum, they often produce audible clicks. Therefore, circuits with poor RF suppression capabilities can inadvertently demodulate RF signals from nearby cell phones, introducing undesirable low-frequency noise. To accurately assess a circuit's performance, it must be tested in an RF environment that mirrors real-world usage conditions. This paper discusses a comprehensive approach for measuring the RF noise suppression capability of integrated circuits. The RF rejection test exposes the board to controlled RF signal levels that simulate potential interference encountered during normal operation. This standardized methodology ensures consistent and repeatable test outcomes, facilitating the selection of circuits with superior resistance to RF noise. The device under test (DUT) can be placed near an active cell phone to evaluate its RF sensitivity, but achieving precise and reproducible measurements requires a fixed setup. To address this, an RF test anechoic chamber provides a highly controlled RF field similar to what a typical mobile phone generates. In our experiments, we evaluated the RF suppression performance of two dual op-amps: the MAX4232 from Maxim and a competing product (X). Figure 1: RF Noise Suppression Capability Measurement Circuit for Dual Op-Amps (Online) The RF suppression test circuit shown in Figure 1 demonstrates how the dual op-amps are connected for evaluation. Each op-amp is configured as an AC amplifier, with the output set to 1.5V DC (VCC = 3V) when no AC input is present. The inverting input is grounded via a 1.5-inch loop (analog input PC lead) to simulate the effects of an actual lead acting as an antenna at the operating frequency to capture and demodulate RF signals. A voltmeter is connected to measure and quantify the RF noise rejection of the op-amp. Figure 2: RF Noise Suppression Capability Measurement Device Maxim's RF test setup (Figure 2) generates the RF field necessary for testing the RF suppression capability. The shielded anechoic chamber functions similarly to a Faraday cage, with ports for connecting power supplies and output monitors. The following equipment is connected to form the test system: The signal generator creates an RF modulated signal at the desired frequency and sends it to the power amplifier. The power amplifier's output is monitored through a directional coupler connected to the power meter. The computer controls the signal generator's frequency range, modulation type, modulation percentage, and amplifier output power to establish the required RF field. The electric field is emitted through the planar antenna inside the shielded anechoic chamber and is precisely calibrated to produce a uniform, repeatable electric field. By employing this setup, we were able to accurately measure the RF noise suppression performance of the MAX4232 and its competitor, providing valuable insights into their respective RF rejection capabilities. These tests underscore the importance of considering RF interference in modern circuit designs and highlight the necessity of rigorous testing methodologies to ensure optimal performance in real-world scenarios. Tape Wrapping Machine,Wire Wrapping Machine,Box Wrapping Machine,Bottle Wrapping Machine Kunshan Bolun Automation Equipment Co., Ltd , https://www.bolunmachinery.com