GC5018_06 Datasheet, PDF (35/134 Pages) Texas Instruments – 8-CHANNEL WIDEBAND RECEIVER

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sync
delay
interrupt
integration time
interval time
GC5018
8-CHANNEL WIDEBAND RECEIVER
SLWS169A – MAY 2005 – REVISED NOVEMBER 2005
interrupt
interrupt
integration time
interval time
integration time
sync
event
integration
start
integration
start
integration
start
Figure 3-27. DDC RMS Power Meter Timing
Each DDC channel includes an RMS power meter which is used to measure the total power within the
channel pass band.
The power meter samples the I and Q data stream after the PFIR filter. Both 18 bit I and Q data are
squared, summed, and then integrated over a period determined by a programmable counter. The
integration time is a 16 bit word which is programmed into the 18 bit counter.
There is a programmable 18 bit interval timer which sets the interval over which power measurements are
made. The timer counts in increments of 1024 samples. This allows the user to select intervals from 1 x
1024 samples up to 256 x 1024 samples. For UMTS systems with sample rate rate at 7.68 MHz, the
power meter interval range is from 133 µS to 34.1 mS. For a CDMA system with the sample rate at
2.4576 MHz, the power meter interval range is 417 µS to 107 mS.
The power measurement process starts with a sync event. The integration will start at sync event +3 chips
+ sync_delay. The 8 bit delay register permits delays from 1 to 256 samples after sync. The integration will
continue until the integration count is met. At that point, the result in the 55 bit accumulator is transferred
to the read holding register and an interrupt is generated indicating the power value is ready to read. The
interval counter continues until the programmed interval count is reached. When reached, the integration
counter and the interval counter start over again. Each time the integration count is reached, the 55 result
bits are again transferred to the read register overwriting the previous value and an interrupt is generated
signifying the data is ready to be read. Failure to read the data timely will result in overwriting the previous
interval measurement.
Sync starts the process. Whenever a sync is received, all the counters are reset to zero no matter what
the status.
For UMTS, I and Q are calculated and the integrated power is read. When in CDMA mode the power is
calculated for both the A ( Signal ) path and the B ( Diversity) signal. As a result, there are two 55-bit
words representing the Signal and Diversity when in CDMA mode.
The power read is:
power = [ (I² + Q²) × (N × 4 + 1) ] where N is the integration count.
VARIABLE
pmeter_result_a(54:0)
pmeter_result_b(54:0)
pmeter_sqr_sum_ddc(15:0)
pmeter_sync_delay_ddc(7:0)
pmeter_interval_ddc(7:0)
ssel_pmeter(2:0)
pmeter_sync_disable
PROGRAMMING
DESCRIPTION
55 bit UMTS or CDMA mode A channel power measurement result.
55 bit CDMA mode B channel power measurement result.
Integration (square and sum) count in increments of four samples.
Sync delay count in samples.
The measurement interval in increments of 2048 samples. This value must be greater than SQR_SUM.
Sync source selection.
Turns off the sync to the channel power meter. This can be used to individually turn off syncs to a
channels power meter while still having syncs to other power meters on the chip.
RECEIVE DIGITAL SIGNAL PROCESSING
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