16-MHz oscillator example

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16-MHz oscillator example

In this section, the steps and guidelines described in the previous section are put into

practice in order to design a 16-MHz oscillator.

The first step concerns the discrete components selection:

●

The STMicroelectronics non-buffered inverter 741VGU04STR operating with VDD =

3.3 is selected for this application. In order to make the inverter act as an amplifier, a

2M

Ω resistor is put between its input and output pads (Rf = 2M)

●

The 16-Mhz quartz CQ is selected. C1 and C2 are selected according to the Quartz

specification. According to the quartz characteristics, a loading capacitor of 20pF

makes the quartz operate at its16 MHz parallel frequency. Theoretically, if we consider

an 8pF stray capacitance, C1 and C2 are calculated using the formula on Section 3.2

on page 8.

C1 = C2 = 24pF.

The standard value of 22pF is taken for both C1 and C2.

After soldering these components without the Rs resistor, the oscillator output signal is

captured in the following figure.

The signal obtained is not symmetric. Therefore, an Rs resistor is put between the inverter

output and the quartz. To start, a potentiometer is put between these two nodes and with a

variable Rs resistor, the following signal is obtained for Rs = 1 K

Ω.