BC41B143A-ds-001Pe CSR, BC41B143A-ds-001Pe Datasheet - Page 57

• Manufacturer Part Number: BC41B143A-ds-001Pe
• Description: Blue Core ROM
• Manufacturer: CSR

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
C
C
int
trim
trim
C
C
t2
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
L
R
m
m
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.
This material is subject to CSR’s non-disclosure agreement
BC41B143A-ds-001Pe
Page 57 of 102
Production Information
© Cambridge Silicon Radio Limited 2005