BC352239A Datasheet, PDF (52/116 Pages) List of Unclassifed Manufacturers – BlueCore 3-Multimedia External

Device Terminal Descriptions
8.3 Crystal Oscillator (XTAL_IN, XTAL_OUT)
The BlueCore3-Multimedia External RF local oscillator and internal digital clocks are derived from the reference
clock at the BlueCore3-Multimedia External XTAL_IN input. This reference may be either an external clock or
from a crystal connected between XTAL_IN and XTAL_OUT. The external reference clock mode is described in
Section 8.2.
8.3.1 XTAL Mode
BlueCore3-Multimedia External contains a crystal driver circuit. This operates with an external crystal and
capacitors to form a Pierce oscillator.
g_m
-
C_trim
C_int
C _trim
C_t2
C_t1
Figure 8.13: Crystal Driver Circuit
Figure 8. shows an electrical equivalent circuit for a crystal. The crystal appears inductive near its resonant
frequency. It forms a resonant circuit with its load capacitors.
C_m
L_m
R_m
C_o
Figure 8.14: Crystal Equivalent Circuit
The resonant frequency may be trimmed with the crystal load capacitance. BlueCore3-Multimedia External
contains variable internal capacitors to provide a fine trim.
The BlueCore3-Multimedia External driver circuit is a transconductance amplifier. A voltage at XTAL_IN
generates a current at XTAL_OUT. The value of transconductance is variable and may be set for optimum
performance.
BC352239A-ds-001Pc
© Cambridge Silicon Radio Limited 2004
Production Information
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