49 of 70
RF6001
Rev A3 DS050929
7628 Thorndike Road, Greensboro, NC 27409-9421 · For sales or technical
support, contact RFMD at (+1) 336-678-5570 or sales-support@rfmd.com.
Part of the POLARIS™ TOTAL RADIO™ Solution
Tuning Gain Calibration
PLL employs a tuning gain calibration algorithm to compensate for tuning gain variations in the integrated VCO’s. This system
eliminates loop gain and bandwidth variations across the VCO tuning range, ensuring that the GSM spectral mask is met. It is
recommended to set the KV_EN bit to true (1) to allow the system to calibrate. Calibration takes approximately 20
μs after the
loop has attained lock.
Lock Detection
The PLL contains a lock detect circuit which can be routed to the “lock-detect/test output” LDTO pin via the test multiplexer.
This circuit provides a rough indication of whether the PLL is operating properly. The LDTO pin voltage will move from ground to
VDD when the loop is close to lock for several cycles of the loop reference frequency. The LDTO pin voltage will return to ground
if the PLL is out of lock. This signal can be monitored in transmit mode to shut down the transmitter if the PLL/VCO system
fails.
Frequency Control
The fractional-N PLL provides very fine frequency resolution capability, requiring a total of 36 bits to set the frequency. In most
cellular systems it is acceptable to have much coarser frequency control. Fine frequency control can be separated into an AFC
(automatic frequency control) register.
The frequency of the PLL/VCO is primarily determined by two registers: the offset register, OFFS(17:0); and, the AFC register,
AFC(17:0). The OFFS register value programs the VCO frequency in multiples of 5kHz. With 18 bits, this gives a range of
2^18*5kHz=1.31GHz.
In order to cover all cellular bands, a base frequency is used, determined by the FBASE(1:0) bits, as shown in the following
table.
The equation for the PLL/VCO frequency is:
The change in frequency versus the AFCD is as follows:
Each step on AFCD will change the TX frequency (both bands) by
In high band RX mode, the LO frequency will change by the same amount.
In low band RX mode, the LO frequency will change by
FBASE(1:0)
FBASE
Frequency Range
Comment (Freq. Band)
00
0Hz
0 to 1310.72MHz
GSM/US Cellular
01
832MHz
832MHz to 2142.72MHz
DCS/PCS
10
1664MHz
1664MHz to 2974.72MHz
DCS/PCS/W-CDMA
11
1664MHz
1664MHz to 2974.72MHz
DCS/PCS/W-CDMA
F
VCO
F
BASE
OFFS
5kHz
AFCD
26MHz
2
24
------------------
⎝⎠
⎛⎞
×
+
×
+
=
ΔF
AFCD
F
REFERENCE
2
24
--------------------------------
⋅
=
AFCD
2
24
F
REFERENCE
--------------------------------
ΔF
⋅
=
26MHz
2
24
------------------
1.55Hz
≈
1
2
---
26MHz
2
24
------------------
0.775Hz
≈
⋅
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