TRF372017 Datasheet, PDF (44/62 Pages) Texas Instruments – Integrated IQ Modulator PLL/VCO

TRF372017
SLWS224C – AUGUST 2010 – REVISED MAY 2012
Setup Example for Fractional Mode
Suppose the following operating characteristics are desired for Fractional mode operation:
• f_REF = 40 MHz (reference input frequency)
• Step at RF = 5 MHz (RF channel spacing)
• f_RF = 1,600,000,045 Hz (RF frequency)
The VCO range is 2400 MHz to 4800 MHz. Therefore:
• LO_DIV_SEL = 2
• f_VCO = LO_DIV_SEL × 1,600,000,045 Hz = 3,200,000,090 Hz
In order to keep the frequency of the prescaler below 3000 MHz:
• PLL_DIV_SEL = 2
Using a typical f_PFD of 20 MHz:
• RDIV = 2
• NINT = 80
• NFRAC = 75
NINT ≥ 75; therefore, select the 8/9 prescaler.
f_N,Max = 3200 MHz/(2 × 8) = 200 MHz < 375 MHz
The actual frequency at RF is:
• f_RF = 1600000044.9419 Hz
For a frequency error of –0.058 Hz.
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Fractional Mode Setup
Optimal operation of the PLL in fractional mode requires several additional register settings. Recommended
values are listed in Table 3. Optimal performance may require tuning the MOD_ORD, ISOURCE_SINK, and
ISOURCE_TRIM values according to the chosen frequency band.
Table 3. Fractional Mode Register Settings
REGISTER BIT
EN_ISOURCE
EN_DITH
MOD_ORD
DITH_SEL
DEL_SD_CLK
EN_LD_ISOURCE
ISOURCE_SINK
ISOURCE_TRIM
REGISTER ADDRESSING
Reg4B18
Reg4B25
Reg4B[27..26]
Reg4B28
Reg4B[30..29]
Reg5B31
Reg7B19
Reg7B[22..20]
RECOMMENDED VALUE
1
1
B[27..26] = [10]
0
B[30..29] = [10]
0
0
B[22..20] = [100]
SELECTING THE VCO AND VCO FREQUENCY CONTROL
To achieve a broad frequency tuning range, the TRF372017 includes four VCOs. Each VCO is connected to a
bank of capacitors that determine its valid operating frequency. For any given frequency setting, the appropriate
VCO and capacitor array must be selected.
The device contains logic that will automatically select the appropriate VCO and capacitor bank. Set bit EN_CAL
to initiate the calibration algorithm. During the calibration process, the device will select a VCO and a capacitor
state so that VTune matches the reference voltage set by VCO_CAL_REF_n. Accuracy of the tune is increased
through bits CAL_ACC_n. Since a calibration begins immediately when EN_CAL is set, all registers must contain
valid value prior to initiating calibration.
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