BC41B143A-DS-001PE Datasheet, PDF (57/102 Pages) List of Unclassifed Manufacturers – BlueCpre 4-ROM Single Chip Bluetooth v2.0 System with EDR

Device Terminal Descriptions
10.3 Crystal Oscillator (XTAL_IN, XTAL_OUT)
The BlueCore4-ROM RF local oscillator and internal digital clocks are derived from the reference clock at the
BlueCore4-ROM 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 10.2.
10.3.1 XTAL Mode
BlueCore4-ROM 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 10.6: Crystal Driver Circuit
Figure 10.7 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 10.7: Crystal Equivalent Circuit
The resonant frequency may be trimmed with the crystal load capacitance. BlueCore4-ROM contains variable
internal capacitors to provide a fine trim.
The BlueCore4-ROM 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.
BC41B143A-ds-001Pe
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Production Information
© Cambridge Silicon Radio Limited 2005
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