Monday, May 18, 2015

An Introduction To Rf Circuit Design

RF circuits transmit and receive radio signals.


Though they come from the same basic principles as direct current (DC) circuits, radio frequency (RF) circuits have more dynamic, complex issues. Because high frequencies have sensitivity to capacitance and inductance, you must design and build RF circuits with care.


Antenna Design


Many RF circuits receive or transmit signals, and both need an antenna. Antennas are sized and constructed to maximize the signals they receive or transmit. Different antenna designs accommodate single or multiple frequencies, long-wave radio, microwave or cell phone signals.


Stray Capacitance


High frequencies make tiny capacitance differences important. Tuning can be affected by stray, unplanned capacitance problems, and excessive capacitance can load down signals. Designers must specify low-capacitance wire and lay circuit boards out carefully to prevent stray capacitance issues.


Shielding


Circuits can transmit RF signals even if you don't want them to. Lengths of wire can become antennas, causing interference with other equipment. Use of shielded cable and connecting one end of the shield jacket to a solid earth ground prevent this. RF circuits are enclosed in grounded metal cages.


Crystal Oscillators


Small slivers of quartz crystal resonate at radio frequencies. Used in transistor circuits, crystals make highly stable oscillators. Time and temperature do not affect their frequency.

Tags: receive transmit, transmit signals