参数资料
型号: MAX2870EVKIT#
厂商: Maxim Integrated
文件页数: 15/24页
文件大小: 0K
描述: EVAL KIT MAX2870
标准包装: 1
系列: *
MAX2870
23.5MHz to 6000MHz Fractional/
Integer-N Synthesizer/VCO
Voltage-Controlled Oscillator
The fundamental VCO frequency of the device guarantees
gap-free coverage from 3.0GHz to 6.0GHz using four
Table 3. ADC VCO Status
ADC VCO STATUS
individual VCO core blocks with 16 sub-bands within
each block. Connect the output of the loop filter to the
TUNE input. The TUNE input is used to control the VCO.
Tune ADC
A 3-bit ADC is used to read the VCO tuning voltage. The
ADC value can be read back by bits 22:20 in register 6.
The ADC uses the ranges shown in Table 3.
Note that the digital or analog lock detect might still be
valid when the tuning voltage is out of the compliance
range.
000
001
010
011
100
101
110
111
Out-of-lock, V TUNE < 0.5V
In-lock, 0.5V < V TUNE < 0.7V
In-lock, 0.7V < V TUNE < 1.3V
Not used
Not used
In-lock, 1.3V < V TUNE < 2.1V
In-lock, 2.1V < V TUNE < 2.5V
Out-of-lock, V TUNE > 2.5V
VCO Autoselect (VAS) State Machine
An internal VCO autoselect state machine is initiated
when register 0 is programmed to automatically select
the correct VCO if bit VAS_SHDN = 0 (register 3, bit 25). If
VAS_SHDN = 1, then the VCO can be manually selected
by bits VCO.
The state machine clock, f BS , must be set to 50kHz. This
is set by the BS bits. The formula for setting BS is:
BS = f PFD /50kHz
where f PFD is the phase-detector frequency. The BS (regis-
ter 4, bits 19:12) value should be rounded to the nearest
integer. If the calculated BS is higher than 1023, then set
BS = 1023. If f PFD is lower than 50kHz, then set BS = 1.
The time needed to select the correct VCO is 10/f BS .
The RETUNE (register 3, bit 24) bit is used to enable or
disable the VAS auto-retune function. Should the 3-bit
TUNE ADC detect that the VCO control voltage (V TUNE )
has drifted into the 000 or 111 state, the VAS will initiate
an auto-retune if RETUNE = 1. If RETUNE = 0, then this
function is disabled.
Maxim Integrated
Phase Shift Mode
After achieving lock, the phase of the RF output can
be changed in increments of P/M x 360 N . The absolute
phase cannot be determined, but it can be changed
relative to the current phase.
To change the phase, do the following:
1) Achieve lock at the desired frequency.
2) Set the increment of phase relative to the current phase
by setting P = M x {desired_phase_change}/360 N .
3) Enable the phase change by setting CDM = 10.
4) Reset CDM = 00.
Low-Spur Mode
The device offers three modes for the sigma-delta modu-
lator. Low-noise mode offers lower in-band noise at the
expense of spurs. The spurs can be reduced by setting
SDN = 10 (register 2, bits 30:29) or SDN = 11 for different
modes of dithering. The user can determine which mode
works best for their application.
15
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