BK4819

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Page 5 of 22

1.2.5 Crystal Oscillator

BK4819 integrates a low-power amplitude-regulated 26MHz crystal oscillator.

The 26MHz crystal oscillator not only provides the reference frequency for the RF

synthesizer, but also provides clock for digital part. The circuit diagram of the

26MHz crystal oscillator is shown in Figure 4.

The 26 MHz crystal oscillator is designed for use with a quartz crystal in parallel

resonant mode. To achieve correct oscillation frequency, the load capacitance

must match the specification in the crystal datasheet. Figure 4 on next page

shows how the crystal is connected to the 26 MHz crystal oscillator. C1 and C2

are ceramic SMD (Surface Mount Device) capacitors connected between each

crystal terminal and ground. Cvar is an adjustable capacitor for frequency

calibration.

Figure 4. Circuit Diagram of the 26MHz Crystal Oscillator

in which, Cpar is parasitic capacitance including PCB trace capacitance and pin

input capacitance. The value of Cpar is about 1pF.

1.2.6 Power Supply Decoupling

Proper power-supply decoupling must be used for optimum performance. The

placement and size of the decoupling capacitors and the power supply filtering

are very important to achieve the best performance in an application.