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| 型号： | EVAL-ADF4350EB2Z |
| 厂商： | Analog Devices Inc |
| 文件页数： | 15/32页 |
| 文件大小： | 0K |
| 描述： | EVALUATION BOARD 2 FOR ADF4350 |
| 标准包装： | 1 |
| 主要目的： | 计时，频率合成器 |
| 嵌入式： | 否 |
| 已用 IC / 零件： | ADF4350 |
| 主要属性： | 带 VCO 的单路分数-N 和整数-N PLL |
| 次要属性： | USB 接口 |
| 已供物品： | 板，缆线，CD |
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ADF4350
Rev. A | Page 22 of 32
The programmable modulus is also very useful for multi-
standard applications. If a dual-mode phone requires PDC
and GSM 1800 standards, the programmable modulus is a
great benefit. PDC requires 25 kHz channel step resolution,
whereas GSM 1800 requires 200 kHz channel step resolution.
A 13 MHz reference signal can be fed directly to the PFD, and
the modulus can be programmed to 520 when in PDC mode
(13 MHz/520 = 25 kHz).
The modulus needs to be reprogrammed to 65 for GSM 1800
operation (13 MHz/65 = 200 kHz).
It is important that the PFD frequency remain constant (13 MHz).
This allows the user to design one loop filter for both setups
without running into stability issues. It is important to remem-
ber that the ratio of the RF frequency to the PFD frequency
principally affects the loop filter design, not the actual channel
spacing.
CYCLE SLIP REDUCTION FOR FASTER LOCK TIMES
As outlined in the Low Noise and Low Spur Mode section, the
ADF4350 contains a number of features that allow optimization
for noise performance. However, in fast locking applications,
the loop bandwidth generally needs to be wide, and therefore,
the filter does not provide much attenuation of the spurs. If
the cycle slip reduction feature is enabled, the narrow loop
bandwidth is maintained for spur attenuation but faster lock
times are still possible.
Cycle Slips
Cycle slips occur in integer-N/fractional-N synthesizers when
the loop bandwidth is narrow compared to the PFD frequency.
The phase error at the PFD inputs accumulates too fast for the
PLL to correct, and the charge pump temporarily pumps in the
wrong direction. This slows down the lock time dramatically.
The ADF4350 contains a cycle slip reduction feature that extends
the linear range of the PFD, allowing faster lock times without
modifications to the loop filter circuitry.
When the circuitry detects that a cycle slip is about to occur,
it turns on an extra charge pump current cell. This outputs a
constant current to the loop filter, or removes a constant
current from the loop filter (depending on whether the VCO
tuning voltage needs to increase or decrease to acquire the new
frequency). The effect is that the linear range of the PFD is
increased. Loop stability is maintained because the current
is constant and is not a pulsed current.
If the phase error increases again to a point where another cycle
slip is likely, the ADF4350 turns on another charge pump cell.
This continues until the ADF4350 detects the VCO frequency
has gone past the desired frequency. The extra charge pump
cells are turned off one by one until all the extra charge pump
cells have been disabled and the frequency is settled with the
original loop filter bandwidth.
Up to seven extra charge pump cells can be turned on. In most
applications, it is enough to eliminate cycle slips altogether,
giving much faster lock times.
Setting Bit DB18 in the Register 3 to 1 enables cycle slip
reduction. Note that the PFD requires a 45% to 55% duty cycle
for CSR to operate correctly. If the REFIN frequency does not
have a suitable duty cycle, the RDIV2 mode ensures that the
input to the PFD has a 50% duty cycle.
SPURIOUS OPTIMIZATION AND FAST LOCK
Narrow loop bandwidths can filter unwanted spurious signals,
but these usually have a long lock time. A wider loop bandwidth
will achieve faster lock times, but a wider loop bandwidth may
lead to increased spurious signals inside the loop bandwidth.
The fast lock feature can achieve the same fast lock time as the
wider bandwidth, but with the advantage of a narrow final loop
bandwidth to keep spurs low.
FAST-LOCK TIMER AND REGISTER SEQUENCES
If the fast-lock mode is used, a timer value is to be loaded into
the PLL to determine the duration of the wide bandwidth mode.
When Bits [DB16:DB15] in Register 3 are set to 0, 1 (fast-lock
enable), the timer value is loaded by the 12–bit clock divider
value. The following sequence must be programmed to use
fast lock:
1.
Initialization sequence (see the Initialization Sequence
section) occurs only once after powering up the part.
2.
Load Register 3 by setting Bits [DB16:DB15] to 0, 1 and
the chosen fast-lock timer value [DB14:DB3]. Note that
the duration the PLL remains in wide bandwidth is equal
to the fast-lock timer/fPFD.
FAST LOCK—AN EXAMPLE
If a PLL has reference frequencies of 13 MHz and fPFD = 13 MHz
and a required lock time of 50 μs, the PLL is set to wide bandwidth
for 40 μs. This example assumes a modulus of 65 for channel
spacing of 200 kHz. This example does not account for the time
required for VCO band select.
If the time period set for the wide bandwidth is 40 μs, then
Fast-Lock Timer Value = Time in Wide Bandwidth × fPFD/MOD
Fast-Lock Timer Value = 40 μs × 13 MHz/65 = 8
Therefore, a value of 8 must be loaded into the clock divider
value in Register 3 in Step 1 of the sequence described in the
Fast-Lock Timer and Register Sequences section.
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相关代理商/技术参数 |
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|---|---|
| EVAL-ADF4351EB1Z | 功能描述:BOARD 1 EVAL FOR ADF4351 RoHS:否 类别:编程器，开发系统 >> 评估演示板和套件 系列:* 标准包装:1 系列:- 主要目的:电信，线路接口单元（LIU） 嵌入式:- 已用 IC / 零件:IDT82V2081 主要属性:T1/J1/E1 LIU 次要属性:- 已供物品:板，电源，线缆，CD 其它名称:82EBV2081 |
| EVAL-ADF4360-0EB1 | 制造商:AD 制造商全称:Analog Devices 功能描述:Integrated Synthesizer and VCO |
| EVAL-ADF4360-1EB1 | 制造商:Analog Devices 功能描述:Evaluation Board For ADF4360-1 |
| EVAL-ADF4360-1EBZ1 | 功能描述:BOARD EVALUATION FOR ADF4360-1 RoHS:是 类别:编程器，开发系统 >> 评估演示板和套件 系列:- 产品培训模块:Obsolescence Mitigation Program 标准包装:1 系列:- 主要目的:电源管理，电池充电器 嵌入式:否 已用 IC / 零件:MAX8903A 主要属性:1 芯锂离子电池 次要属性:状态 LED 已供物品:板 |
| EVAL-ADF4360-2EB1 | 制造商:Analog Devices 功能描述:EVALUATION BOARD FOR ADF4360-2 |
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