參數(shù)資料
型號: AD9517-1ABCPZ
廠商: Analog Devices Inc
文件頁數(shù): 28/80頁
文件大?。?/td> 0K
描述: IC CLOCK GEN 2.5GHZ VCO 48LFCSP
標(biāo)準(zhǔn)包裝: 1
類型: 時(shí)鐘發(fā)生器,扇出配送
PLL:
輸入: CMOS,LVDS,LVPECL
輸出: CMOS,LVDS,LVPECL
電路數(shù): 1
比率 - 輸入:輸出: 1:12
差分 - 輸入:輸出: 是/是
頻率 - 最大: 2.65GHz
除法器/乘法器: 是/無
電源電壓: 3.135 V ~ 3.465 V
工作溫度: -40°C ~ 85°C
安裝類型: 表面貼裝
封裝/外殼: 48-LFCSP
供應(yīng)商設(shè)備封裝: 48-LFCSP-VQ(7x7)
包裝: 托盤
AD9517-1
Data Sheet
Rev. E | Page 34 of 80
Charge Pump (CP)
The charge pump is controlled by the PFD. The PFD monitors
the phase and frequency relationship between its two inputs
and tells the CP to pump up or pump down to charge or
discharge the integrating node (part of the loop filter). The
integrated and filtered CP current is transformed into a voltage
that drives the tuning node of the internal VCO through the LF
pin (or the tuning pin of an external VCO) to move the VCO
frequency up or down. The CP can be set (Register 0x010[6:4])
for high impedance (allows holdover operation), for normal
operation (attempts to lock the PLL loop), for pump up, or for
pump down (test modes). The CP current is programmable in
eight steps from (nominally) 600 A to 4.8 mA. The exact value
of the CP current LSB is set by the CPRSET resistor, which is
nominally 5.1 k. If the value of the resistor that is connected
to the CP_RSET pin is doubled, the resulting charge pump current
range becomes 300 A to 2.4 mA.
On-Chip VCO
The AD9517 includes an on-chip VCO covering the frequency
range shown in Table 2. The calibration procedure ensures that
the VCO operating voltage is centered for the desired VCO
frequency. The VCO must be calibrated when the VCO loop
is first set up, as well as any time the nominal VCO frequency
changes. However, once the VCO is calibrated, the VCO has
sufficient operating range to stay locked over temperature and
voltage extremes without needing additional calibration. See the
VCO Calibration section for additional information.
The on-chip VCO is powered by an on-chip, low dropout
(LDO), linear voltage regulator. The LDO provides some
isolation of the VCO from variations in the power supply
voltage level. The BYPASS pin should be connected to ground
by a 220 nF capacitor to ensure stability. This LDO employs the
same technology used in the anyCAP line of regulators from
Analog Devices, Inc., making it insensitive to the type of
capacitor used. Driving an external load from the BYPASS pin
is not supported.
Note that the reference input signal must be present and the
VCO divider must not be static during VCO calibration.
PLL External Loop Filter
When using the internal VCO, the external loop filter should be
referenced to the BYPASS pin for optimal noise and spurious
performance. An example of an external loop filter for a PLL
that uses the internal VCO is shown in Figure 47. The third-
order design shown in Figure 47 usually offers best performance.
A loop filter must be calculated for each desired PLL configuration.
The values of the components depend upon the VCO frequency,
the KVCO, the PFD frequency, the CP current, the desired loop
bandwidth, and the desired phase margin. The loop filter affects
the phase noise, loop settling time, and loop stability. A basic
knowledge of PLL theory is helpful for understanding loop filter
design. ADIsimCLK can help with the calculation of a loop
filter according to the application requirements.
When using an external VCO, the external loop filter should
be referenced to ground. See Figure 48 for an example of an
external loop filter for a PLL using an external VCO.
LF
VCO
CHARGE
PUMP
CP
BYPASS
C1
C2
C3
R1
31pF
R2
CBP = 220nF
AD9517-1
06425-
065
Figure 47. Example of External Loop Filter for a PLL Using the Internal VCO
CLK/CLK
EXTERNAL
VCO/VCXO
CHARGE
PUMP
CP
C1
C2
C3
R1
R2
AD9517-1
06425-
265
Figure 48. Example of External Loop Filter for a PLL Using an External VCO
PLL Reference Inputs
The AD9517 features a flexible PLL reference input circuit that
allows either a fully differential input or two separate single-
ended inputs. The input frequency range for the reference
inputs is specified in Table 2. Both the differential and
the single-ended inputs are self-biased, allowing for easy
ac coupling of input signals.
The differential input and the single-ended inputs share the two
pins, REFIN and REFIN (REF1 and REF2, respectively). The
desired reference input type is selected and controlled by Register
When the differential reference input is selected, the self-bias
level of the two sides is offset slightly (~100 mV, see Table 2) to
prevent chattering of the input buffer when the reference is slow
or missing. This increases the voltage swing that is required of
the driver and overcomes the offset. The differential reference
input can be driven by either ac-coupled LVDS or ac-coupled
LVPECL signals.
The single-ended inputs can be driven by either a dc-coupled
CMOS level signal or an ac-coupled sine wave or square wave.
Each single-ended input can be independently powered down
when not needed to increase isolation and reduce power. Either
a differential or a single-ended reference must be specifically
enabled. All PLL reference inputs are off by default.
The differential reference input is powered down whenever the
PLL is powered down or when the differential reference input is
not selected. The single-ended buffers power down when the
PLL is powered down and when their individual power-down
registers are set. When the differential mode is selected, the
single-ended inputs are powered down.
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