HMC1197LP7FE Datasheet, PDF (20/57 Pages) Hittite Microwave Corporation – Fixed Wireless or WLL

HMC1197LP7FE
v03.0314
Wideband Direct Quadrature Modulator
w/ Fractional-N PLL & VCO, 100 - 4000 MHz
Suppose the HMC1197LP7FE output frequency is to operate at 2.01 GHz. Our example crystal frequency
is f_xtal = 50 MHz, R=1, and m=0 (Figure 37), hence T_FSM = 20 ns (50 MHz). Note, when using AutoCal, the
maximum AutoCal Finite State Machine (FSM) clock cannot exceed 50 MHz (see Reg 0Ah[14:13]). The
FSM clock does not affect the accuracy of the measurement, it only affects the time to produce the result.
This same clock is used to clock the 16 bit VCO serial port.
If time to change frequencies is not a concern, then one may set the calibration time for maximum accuracy,
and therefore not be concerned with measurement resolution.
Using an input crystal of 50 MHz (R=1 and fpd=50 MHz) the times and accuracies for calibration using
(EQ 6) and (EQ 8) are shown in Table 10 Where minimal tuning time is 1/8^th of the VCO band spacing.
Across all VCOs, a measurement resolution better than 800 kHz will produce correct results. Setting
m = 0, n = 5, provides 781 kHz of resolution and adds 8.6 µs of AutoCal time to a normal frequency hop.
Once the AutoCal sets the final switch value, 8.64 µs after the frequency change command, the fractional
register will be loaded, and the loop will lock with a normal transient predicted by the loop dynamics. Hence
as shown in this example that AutoCal typically adds about 8.6 µs to the normal time to achieve frequency
lock. Hence, AutoCal should be used for all but the most extreme frequency hopping requirements.
Table 10. AutoCal Example with F_xtal = 50 MHz, R = 1, m = 0
Control Value
n
Reg0Ah[2:0]
2n
Tmmt
(µs)
Tcal
(µs)
Ferr Max
0
0
1
0.02
4.92
± 25 MHz
1
1
2
0.04
5.04
± 12.5 MHz
2
2
4
0.08
5.28
± 6.25 MHz
3
3
8
0.16
5.76
± 3.125 MHz
4
5
32
0.64
8.64
± 781 kHz
5
6
64
1.28
12.48
± 390 kHz
6
7
128
2.56
20.16
± 195 kHz
7
8
256
5.12
35.52
± 98 kHz
1.2.1.5 Manual VCO Calibration for Fast Frequency Hopping
If it is desirable to switch frequencies quickly it is possible to eliminate the AutoCal time by calibrating
the VCO in advance and storing the switch number vs frequency information in the host. This can be
done by initially locking the HMC1197LP7FE on each desired frequency using AutoCal, then reading,
and storing the selected VCO switch settings. The VCO switch settings are available inReg 15h[8:1] after
every AutoCal operation. The host must then program the VCO switch settings directly when changing
frequencies. Manual writes to the VCO switches are executed immediately as are writes to the integer and
fractional registers when AutoCal is disabled. Hence frequency changes with manual control and AutoCal
disabled, requires a minimum of two serial port transfers to the HMC1197LP7FE, once to set the VCO
switches, and once to set the PLL frequency.
If AutoCal is disabled Reg 0Ah[11]=1, the VCO will update its registers with the value written via Reg
15h[8:1] immediately.
1.2.2
Registers required for Frequency Changes in Fractional Mode
A large change of frequency, in fractional mode (Reg 06h[11]=1), may require Main Serial Port writes to:
1. The integer register intg, Reg 03h (only required if the integer part changes)
2. Manual VCO Tuning Reg 15h only required for manual control of VCO if Reg 0Ah[11]=1 (AutoCal
disabled)
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