W3020 Datasheet, PDF (31/44 Pages) Agere Systems – GSM Multiband RF Transceiver

Advance Data Sheet
December 1999
W3020 GSM Multiband RF Transceiver
Programming Information (continued)
Filter Tune and dc Offset Correction Timing
Low-Pass Filter Tuning
The W3020 has an internal calibration to improve the accuracy of the low-pass filter bandwidth. The filter tune
operation should be performed each time supply voltage is applied to the device and after restart.
The low-pass filter tuning operation is controlled by 3 bits in the control logic:
n FTR: filter tune request, in the TR register
n C4: low-pass filter bandwidth, in the CONFIG register
n C6: filter tune disable, in the CONFIG register
If the filter tune disable bit (C6) is programmed high, the filter bandwidth is set to the programmed (nominal)
value (see Table 35), and any request for filter tuning from the FTR bit is ignored.
The accuracy of the filter bandwidth can be improved by performing a filter tune calibration. A filter tune can be
performed by setting the filter tune request (FTR) bit in the TR register high and the filter tune disable bit (C6) in
the CONFIG register low. This enables a 13/4 MHz (3.25 MHz) clock to the filter tuning state machine, which
then runs until the tuning is complete and the new filter tune values are stored. The filter tune operation itself
takes
16.5 cycles of the 3.25 MHz clock, or 5.1 µs.
The filter tune operation should be done in receive mode. The receive mode needs to be held active for at least
20 µs to allow for bias start-up.
The dc offset calibration, if requested, is performed after the filter tune is complete. The filter tune operation adds
5.1 µs to the total calibration time when requested at the same time as a dc offset calibration. If a filter tune is
requested while the MOD bits are not set to 111, only the receive bias circuitry is turned on; the rest of the
receive channel remains powered down.
Lucent Technologies Inc.
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