Issue link: https://resources.mouser.com/i/1447260
Würth Elektronik 2022 5 Many EMC problems from electronic devices can be solved with a chip-bead ferrite solution in the EMI signal path. " Broadband Amplifier 5MHz–7GHz Broadband amplifiers are often needed in receiving applications when using antennas to reproduce a wide range of signals with low noise. The bias network is one of the critical aspects of RF circuit design. It determines the amplifier performance over temperature as well as DC bias conditions. The DC voltages applied in an amplifier cannot be applied directly. Therefore, a high-impedance component ensures that the complete RF signal passes through the device and not back through the DC bias circuit. The current bias is seen as a high-impedance element to the RF signal, allowing most information to pass through the device—hence supplying a stable current to the output. A standard inductor does not operate over a wide frequency range, having a smaller resistive area profile (roughly in the range of 200MHz to 2GHz only). For a standard wire-wound ferrite, the parasitics begin to dominate, resulting in capacitance and less inductance. An alternative to providing wide bandwidth for broadband use is to substitute the air coil inductor with WE-CBF HF ferrite beads at L 1 and L 2 (Figure 1 and Figure 2). High impedances in the power supply path above 200Ω can drive the gain. Additionally, impedances lower than 200Ω the RF signal at the output of the gain block will be attenuated. The advantages of using a WE-CBF HF: ■ Wide band of frequencies (broadband) ■ Stable inductance ■ RF signal passes through to output Anti-aliasing filter for Analog-to-Digital- Converter (ADC) It is usually necessary to place an anti-aliasing filter before an analog-to-digital-converter (ADC) to attenuate the unwanted higher frequency noise and signals. The common LC formation of a low pass filter (LPF) may have effects of under damping, which creates a resonant peak at a frequency band around the converter's switching frequency, consequently resulting in the amplification of unwanted switching noises. Using a ferrite bead in series with the inductor will dampen and smooth out the LPF response and act as an impedance transformer. The standard way to design a filter for an ADC includes RC topologies and LC topologies with or without using operational amplifiers (op-amp). As a first-order filter, an RC filter produces a fall of -3dB at its cut-off and a steepness slope of 20dB/decade step down frequency response, which generally is not enough to provide a strong filtering system. An LC filter usually has low resistivity and high inductivity; as a result, minimal damping creates unwanted oscillation. Since an ADC does not have a standard resistive load, when a peak load occurs, the measure of this load can be identified as a resonating peak at the corner frequency. How to solve EMC problems! || The mystery of the buzzing speaker Figure 2: Gain amplifier test board with WE-CBF HF (742861160) (Source: Würth Elektronik) Figure 1: Gain amplifier circuit design. (Source: Würth Elektronik)