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ZHCSIC4C June 2018 – November 2018 LMX2615-SP

PRODUCTION DATA.

封裝選項

機械數(shù)據(jù) (封裝 | 引腳)

HBD|64
- MCSF001

散熱焊盤機械數(shù)據(jù) (封裝 | 引腳)

訂購信息

7.3.7.1 VCO Calibration

To reduce the VCO tuning gain and therefore improve the VCO phase-noise performance, the VCO frequency range is divided into several different frequency bands. The entire range, 7600 to 15200 MHz, covers an octave that allows the divider to take care of frequencies below the lower bound. This creates the need for frequency calibration to determine the correct frequency band given a desired output frequency. The frequency calibration routine is activated any time that the R0 register is programmed with the FCAL_EN = 1. It is important that a valid OSCin signal must present before VCO calibration begins.

The VCO also has an internal amplitude calibration algorithm to optimize the phase noise which is also activated any time the R0 register is programmed.

The optimum internal settings for this are temperature dependent. If the temperature is allowed to drift too much without being re-calibrated, some minor phase noise degradation could result. The maximum allowable drift for continuous lock, ΔT_CL, is stated in the electrical specifications. For this device, a number of 125°C means the device never loses lock if the device is operated under recommended operating conditions.

The LMX2615 allows the user to assist the VCO calibration. In general, there are three kinds of assistance, as shown in Table 4:

Table 4. Assisting the VCO Calibration Speed

ASSISTANCE LEVEL	DESCRIPTION	VCO_SEL	VCO_SEL_FORCE VCO_CAPCTRL_FORCE VCO_DACISET_FORCE	VCO_CAPCTRL VCO_DACISET
No assist	User does nothing to improve VCO calibration speed.	7	0	Dont Care
Partial assist	Upon every frequency change, before the FCAL_EN bit is checked, the user provides the initial starting VCO_SEL	Choose by table	0	Don't Care
Full assist	The user forces the VCO core (VCO_SEL), amplitude settings (VCO_DACISET), and frequency band (VCO_CAPCTRL) and manually sets the value.	Choose by readback	1	Choose by readback

For the no assist method, just set VCO_SEL=7 and this is done. For partial assist, the VCO calibration speed can be improved by changing the VCO_SEL bit according to the frequency. Note that the frequency is not the actual VCO core range, but actually favors choosing the VCO. This is not only optimal for VCO calibration speed, but required for reliable locking.

Table 5. Minimum VCO_SEL for Partial Assist

f_VCO	VCO Core (min)
7600 - 8740 MHz	VCO1
8740 - 10000 MHz	VCO2
10000 - 10980 MHz	VCO3
10980 -12100 MHz	VCO4
12100 - 13080 MHz	VCO5
13080 - 14180 MHz	VCO6
14180 - 15200 MHz	VCO7

For fastest calibration time, it is ideal to use the minimum VCO core as recommended in the previous table. The following table shows typical VCO calibration times for this choice in bold as well as showing how long the calibration time is increased if a higher than necessary VCO core is chosen. Realize that these calibration times are specific to these f_OSC and f_PD conditions specified and at the boundary of two cores, sometimes the calibration time can be increased.

Table 6. Typical Calibration times for f_OSC = f_PD = 100 MHz based on VCO_SEL

f_VCO	VCO_SEL
f_VCO	VCO7	VCO6	VCO5	VCO4	VCO3	VCO2	VCO1
8.1 GHz	650	540	550	440	360	230	110
9.3 GHz	610	530	540	430	320	220	Invalid
10.4 GHz	590	520	530	430	240	Invalid
11.4 GHz	340	290	280	180	Invalid
12.5 GHz	270	170	120	Invalid
13.6 GHz	240	130	Invalid
14.7 GHz	160	Invalid