BCM20713A1KUFBXG Datasheet, PDF (35/65 Pages) Cypress Semiconductor – Single-Chip Bluetooth Transceiver and Baseband Processor

BCM20713 Preliminary Data Sheet
Frequency Trimming
The BCM20713 reference frequency can be set in one of three ways.
• Use the default 20 MHz frequency
• Designate the reference frequency in external NVRAM
• Auto-detect the standard handset reference frequencies using an external LPO clock
The BCM20713 is set to a default frequency of 20 MHz at the factory. For a typical design using a crystal, it is
recommended that the default frequency be used, since this simplifies the design by removing the need for
either external NVRAM or external LPO clock.
If the application requires a frequency other than the default, the value can be stored in an external NVRAM.
Programming the reference frequency in NVRAM provides the maximum flexibility in the selection of the
reference frequency, since any frequency within the specified range for crystal and external frequency reference
can be used. During power-on reset (POR), the device downloads the parameter settings stored in NVRAM,
which can be programmed to include the reference frequency and frequency trim values. Typically, this is how
a PC Bluetooth application is configured.
For applications such as handsets and portable smart communication devices, where the reference frequency
is one of the standard frequencies commonly used, the BCM20713 automatically detects the reference
frequency and programs itself to the correct reference frequency. In order for auto-frequency detection to work
properly, the BCM20713 must have a valid and stable 32.768 kHz external LPO clock present during POR. This
eliminates the need for NVRAM in applications where the external LPO clock is available and an external
NVRAM is typically not used.
Frequency Trimming
The BCM20713 uses a fractional-N synthesizer to digitally fine-tune the frequency reference input to within ±2
ppm tuning accuracy. This trimming function can be applied to either the crystal or an external frequency source
such as a TCXO. Unlike the typical crystal-trimming methods used, the BCM20713 changes the frequency using
a fully digital implementation and is much more stable and unaffected by crystal characteristics or temperature.
Input impedance and loading characteristics remain unchanged on the TCXO or crystal during the trimming
process and are unaffected by process and temperature variations.
The option to use or not use frequency trimming is based on the system designer’s cost trade-off between bill-
of-materials (BOM) cost of the crystal and the added manufacturing cost associated with frequency trimming.
The frequency trimming value can either be stored in the host and written to the BCM20713 as a vendor-specific
HCI command or stored in NVRAM and subsequently recalled during POR.
Frequency trimming is not a substitute for the poor use of tuning capacitors at an crystal oscillator (XTAL).
Occasionally, trimming can help alleviate hardware changes.
Broadcom^®
December 21, 2015 • 20713-DS102-R
Single-Chip Bluetooth Transceiver and Baseband Processor
Page 34
BROADCOM CONFIDENTIAL