AN1017| Application Note
Maxim/Dallas > App Notes > AUTOMOTIVE
WIRELESS, RF, AND CABLE
Keywords: MAX1470, superheterodyne receiver, 315MHz-433MHz receiver, crystal oscillator, quartz crystal oscillators
Mar 27, 2002
APPLICATION NOTE 1017
How to Choose a Quartz Crystal Oscillator for the MAX1470 Superheterodyne Receiver
Quartz crystals are available from various vendors in a variety of shapes and sizes, and can range widely in performance specifications. Some of these specifications include resonance frequency, resonance mode, load capacitance, series resistance, holder capacitance, and drive level. This application note helps in the understanding of these parameters, allowing the user to specify the crystal that is right for their application and one that will give the best results with the MAX1470 superheterodyne receiver circuit. Quartz crystals are available from various vendors in a variety of shapes and sizes, and can range widely in performance specifications. Some of these specifications include resonance frequency, resonance mode, load capacitance, series resistance, holder capacitance, and drive level. Understanding these parameters will allow you to specify the crystal that is right for your application and one that will give you the best results with your MAX1470 circuit. The equivalent circuit of a crystal is s
hown in Figure 1. It consists of the motional elements: resistor, Rs, inductor, Lm, and capacitor, Cm, and a shunt capacitance, Co. The motional elements determine the series resonant frequency and the Q of the resonator. The shunt capacitance, Co, is a function of the crystal electrodes, holder, and leads.
Figure 1. Crystal models. The following details the key performance specifications.
Resonance Frequency
The crystal frequency to be specified is dependent on the frequency you're interested in receiving. Since the MAX1470 uses a 10.7MHz IF with low-side injection, the crystal frequency is given by (all units in MHz):
For 315MHz applications, the crystal frequency is therefore, 4.7547MHz, while for 433.92MHz a 6.6128MHz crystal is needed. Only fundamental mode crystals should be specified (no overtones).
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