Understanding rf circuits with multisim 10

UNDERSTANDING RF CIRCUITS WITH MULTISIM 10 SERIES

The figure below depicts impedance mismatch in high-speed PCB design.ДЇigure3: Characteristic impedance mismatchДue to impedance mismatch, the signal gets distorted. To deliver the power efficiently across the connection, or wire, the impedance must match. The next important factor a design engineer needs to ponder is the impedance match. How impedance match affect the RF circuit design? If the traces are longer than 2 feet, then interconnects must be considered as transmission lines, which would interfere with the propagation of the signal.

Wavelength=Speed of wave/ Frequency= 1.5Г—10^8/25 x 10^6= 6 meters.ДЎ/10th of the wavelength will be 60 centimeters, which would be approximately around 2 feet. Relative Permittivity for FR-4 Material is 4. V=Speed of Light/Sqrt (Relative Permittivity) How quickly signals move through the circuitry, is determined by the speed of light divided by the square root of the relative permittivity of the material. Let us consider a 20 Hertz square wave, and the rise time is about 200ns, frequency is inverse of the rise time we get 25 MHZ. Engineers must find out the highest frequency their design will be dealing with if the traces exceed about 1/10 of the wavelength of that frequency, then engineers must model the interconnect as the transmission line.ДЄbsolute frequency of the waveform may not be the critical aspect, but the fastest rise time will determine the circuitвЂ™s quickest frequency. When we work on SPICE simulation tools, we think wires as an interconnect points, thatвЂ™s not true when we are working with high-speed signals, then all the interconnections have to be treated as a transmission line. Most of the suppliers or manufacturers recommend out particular bypass requirements with any specific design requirements based on the datasheets.

When design engineers work on high-speed PCB design, bypassing/decoupling forms a crucial factor.

UNDERSTANDING RF CIRCUITS WITH MULTISIM 10 SERIES

Since it is a series RLC circuit, the frequency at which the capacitor no longer acts as a capacitor becomes an inductor and no longer decouples the circuit.ДЇigure 2: Realistic approximation of a capacitorД¬ircuits that cover a wide range of frequency must have multiple decoupling capacitors. The realistic approximation of a capacitor is an RLC circuit, a real-world capacitor, has parasitic inductance, and resistance. The decoupling capacitor helps in eliminating most of the noise the circuit encounters.ДЄny real-world circuit that deals with high-speed signals or sensitive low-level signals things turn complicated. In a high-speed PCB design, any active components such as operational amplifiers, microprocessors, or high-density BGA, there are many decoupling capacitors. When we work with real-world power supply, itвЂ™s not perfect since they donвЂ™t have infinite output impedance.ДЄny SPICE simulation tools, it depicts a perfect line, but thatвЂ™s not the reality shown in the figure below.ДЇigure1: Ideal Spice Simulation Why decoupling capacitors must be considered for RF circuit design? Several critical factors influence the RF circuit board design. RF circuit boards find their usage in many upcoming technologies, such as smartphones, sensors, and in many of the military applications. Anything above 3 Gigahertz up to 30 Gigahertz considered as Microwave PCB circuits. PCB circuits which propagates electromagnetic wave between 1 Megahertz and 3 Gigahertz classified as RF circuits. It propagates readily in a vacuum or solid-state through circuit boards or coaxial cables. RF stands for radio frequency, is a form of energy in the modification of time-dependent electromagnetic fields. What are RF Circuits, and how an RF circuits work? Nah, thanks to PCB, which is a multilayered labyrinth of hundreds of copper wires. A Smartphone holds around 11000 centimeters of wire inside it, to connect a speaker, Antenna, GPS, battery, Wi-Fi, sensors, and many more components into a single device.Д«ut where are these wires? Are they invisible like the вЂњInvisible ManвЂќ?

Imagine a world without a Printed Circuit board? Quite unimaginable, the tangled wires would have been all over the places.

Understanding rf circuits with multisim 10