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PDF LTC6945 Data sheet ( Hoja de datos )
| Número de pieza | LTC6945 | |
| Descripción | Ultralow Noise and Spurious 0.35GHz to 6GHz Integer-N Synthesizer | |
| Fabricantes | Linear | |
| Logotipo |  |
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Hay una vista previa y un enlace de descarga de LTC6945 (archivo pdf) en la parte inferior de esta página. Total 28 Páginas | ||
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LTC6945
Features
Ultralow Noise and Spurious
0.35GHz to 6GHz Integer-N
Synthesizer
Description
nn Low Noise Integer-N PLL
nn 350MHz to 6GHz VCO Input Range
nn –226dBc/Hz Normalized In-Band Phase Noise Floor
nn –274dBc/Hz Normalized In-Band 1/f Noise
nn –157dBc/Hz Wideband Output Phase Noise Floor
nn Excellent Spurious Performance
nn Output Divider (1 to 6, 50% Duty Cycle)
nn Low Noise Reference Buffer
nn Output Buffer Muting
nn Charge Pump Supply from 3.15V to 5.25V
nn Charge Pump Current from 250µA to 11.2mA
nn Configurable Status Output
nn SPI Compatible Serial Port Control
nn PLLWizard™ Software Design Tool Support
Applications
nn Wireless Base Stations (LTE, WiMAX, W-CDMA, PCS)
nn Broadband Wireless Access
nn Microwave Data Links
nn Military and Secure Radio
nn Test and Measurement
The LTC®6945 is a high performance, low noise, 6GHz phase-
locked loop (PLL), including a reference divider, phase-
frequency detector (PFD) with phase-lock indicator, charge
pump, integer feedback divider and VCO output divider.
The part features a buffered, programmable VCO output
divider with a range of 1 through 6. The differential, low
noise output buffer has user-programmable output power
ranging from –6dBm to 3dBm, and may be muted through
either a digital input pin or software.
The low noise reference buffer outputs a typical 0dBm
square wave directly into a 50Ω impedance from 10MHz
to 250MHz, or may be disabled through software.
The ultralow noise charge pump contains selectable high
and low voltage clamps useful for VCO monitoring, and
also may be set to provide a V+/2 bias.
All device settings are controlled through a SPI-compatible
serial port.
L, LT, LTC, LTM, Linear Technology and the Linear logo are registered trademarks and
PLLWizard is a trademark of Linear Technology Corporation. All other trademarks are the
property of their respective owners.
Typical Application
LTC6945 Data Converter Sample Clock
3.3V LOOP
0.1µF
BANDWIDTH
~2.3kHz
VTUNE
5V CRYSTEK
CVCSO-914-1000
100MHz
REF 1µF
51.1Ω
1µF
5V
0.1µF
432Ω
570nF
47nF
3.3V
0.1µF
SPI BUS
3.3V
0.1µF
REF– REF+
VREFO+
VREF+ CP VCP+VGVNCOD+
REFO
STAT
LTC6945
GND
GND
CS
SCLK
GND
GND
GND
SDI GND
SDO
VD+
MUTE
fPFD = 25MHz
GND RF– RF+ VRF+
VCO+
VCO–
BB
3.3V 0.01µF
16.5Ω
100pF
1.0µF
100pF
16.5Ω
16.5Ω
100pF
68nH
3.3V
100pF
50Ω
3.3V 0.01µF
68nH
3.3V
100pF
ALT SAMPLE CLOCK
500MHz OR 1GHz
SAMPLE CLOCK
1GHz, 7dBm
6945 TA01b
1GHz Sample Clock Phase Noise
–100
–110
–120
–130
–140
–150
–160
–170
–180
100
DSB INTEGRATION
(100Hz TO 1GHz)
RMS NOISE = 0.014°
RMS JITTER = 39fs
fPFD = 25MHz
BW = 2.3kHz
1k 10k 100k 1M
OFFSET FREQUENCY (Hz)
10M 40M
6945 TA01b
For more information www.linear.com/LTC6945
6945fa
1
1 page  
LTC6945
E lectrical Characteristics The l denotes the specifications which apply over the full operating
junction temperature
otherwise specified.
range, otherwise specifications are at
All voltages are with respect to GND.
TA
=
25°C.
VREF+
=
VREF0+
=
VD+
=
VRF+
=
VVCO+
=
3.3V,
VCP+
=
5V
unless
SYMBOL PARAMETER
Phase Noise and Spurious
LM(MIN)
Output Phase Noise Floor (Note 5)
LM(NORM) Normalized In-Band Phase Noise Floor
LM(NORM –1/f) Normalized In-Band 1/f Phase Noise
LM(IB)
In-Band Phase Noise Floor
Integrated Phase Noise from 100Hz to
40MHz
Spurious
CONDITIONS
RFO[1:0]
RFO[1:0]
=
=
3,
3,
OD[2:0]
OD[2:0]
=
=
1,
2,
ffRRFF
=
=
6GHz
3GHz
RFO[1:0] = 3, OD[2:0] = 3, fRF = 2GHz
RFO[1:0] = 3, OD[2:0] = 4, fRF = 1.5GHz
RFO[1:0] = 3, OD[2:0] = 5, fRF = 1.2GHz
RFO[1:0] = 3, OD[2:0] = 6, fRF = 1.0GHz
ICP = 11.2mA (Notes 6, 7, 8)
ICP = 11.2mA (Notes 6, 9)
(Notes 6, 7, 8, 10)
(Notes 4, 7, 10)
Reference Spur, PLL locked (Notes 4, 7, 10, 11)
MIN TYP MAX
–155
–155
–156
–156
–157
–158
–226
–274
–99
0.13
–102
UNITS
dBc/Hz
dBc/Hz
dBc/Hz
dBc/Hz
dBc/Hz
dBc/Hz
dBc/Hz
dBc/Hz
dBc/Hz
°RMS
dBc
Note 1: Stresses beyond those listed under Absolute Maximum Ratings
may cause permanent damage to the device. Exposure to any Absolute
Maximum Rating condition for extended periods may affect device
reliability and lifetime.
Note 2: The LTC6945I is guaranteed to meet specified performance limits
over the full operating junction temperature range of –40°C to 105°C.
Under maximum operating conditions, air flow or heat sinking may
be required to maintain a junction temperature of 105°C or lower. It is
strongly recommended that the exposed pad (Pin 29) be soldered directly
to the ground plane with an array of thermal vias as described in the
Applications Information section.
Note 3: For 0.9V ≤ VCP ≤ (VCP+ – 0.9V).
Note 4: VCO is Crystek CVCO55CL-0902-0928.
Note 5: fVCO = 6GHz, fOFFSET = 40MHz.
Note 6: Measured inside the loop bandwidth with the loop locked.
Note 7: Reference frequency supplied by Wenzel 501-04608A,
fREF = 10MHz, PREF = 13dBm.
Note 8: Output phase noise floor is calculated from normalized phase
noise floor by LM(OUT) = –226 + 10log10(fPFD) + 20log10(fRF/fPFD).
Note 9: Output 1/f phase noise is calculated from normalized 1/f phase
noise by LM(OUT –1/f) = –274 + 20log10 (fRF) – 10log10 (fOFFSET).
Note 10: ICP = 11.2mA, fPFD = 250kHz, fRF = 914MHz, FILT[1:0] = 3, Loop
BW = 7kHz.
Note 11: Measured using DC1649.
Typical Performance Characteristics
REF Input Sensitivity vs
Frequency
–15
BST = 1
–20 FILT = 0
TJ = 105°C
–25 TJ = 25°C
TJ = –40°C
–30
–35
–40
–45
–50
–55
0 25 50 75 100 125 150 175 200 225 250
FREQUENCY (MHz)
6945 G01
REFO Output Power vs Frequency
4
TJ = 105°C
3 TJ = 25°C
TJ = –40°C
2
1
0
–1
–2
–3
–4
0 25 50 75 100 125 150 175 200 225 250
FREQUENCY (MHz)
6945 G02
For more information www.linear.com/LTC6945
REFO Phase Noise
–140
–145
POUT = 1.45dBm
fREF = 10MHz
BST = 1
FILT = 3
NOTE 7
–150
–155
–160
100
1k 10k 100k 1M 5M
OFFSET FREQUENCY (Hz)
6945 G03
6945fa
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5 Page 
LTC6945
Operation
PHASE/FREQUENCY DETECTOR (PFD)
The phase/frequency detector (PFD), in conjunction with
the charge pump, produces source and sink current pulses
proportional to the phase difference between the outputs
of the R and N dividers. This action provides the necessary
feedback to phase-lock the loop, forcing a phase align-
ment at the PFD’s inputs. The PFD may be disabled with
the CPRST bit which prevents UP and DOWN pulses from
being produced. See Figure 3 for a simplified schematic
of the PFD.
R DIV
N DIV
DQ
RST
DQ
RST
UP
CPRST
DELAY
DOWN
6945 F03
Figure 3. Simplified PFD Schematic
LOCK INDICATOR
The lock indicator uses internal signals from the PFD to
measure phase coincidence between the R and N divider
output signals. It is enabled by setting the LKEN bit in
the serial port register h07, and produces both LOCK and
UNLOCK status flags, available through both the STAT
output and serial port register h00.
The user sets the phase difference lock window time,
tLWW , for a valid LOCK condition with the LKWIN[1:0]
bits. See Table 3 for recommended settings for different
fPFD frequencies and the Applications Information section
for examples.
Table 3. LKWIN[1:0] Programming
LKWIN[1:0]
0
tLWW
3ns
1 10ns
2 30ns
3 90ns
fPFD
>5MHz
≤5MHz
≤1.7MHz
≤550kHz
The PFD phase difference must be less than tLWW for the
COUNTS number of successive counts before the lock
indicator asserts the LOCK flag. The LKCT[1:0] bits found
in register h09 are used to set COUNTS depending upon
the application. See Table 4 for LKCT[1:0] programming
and the Applications Information section for examples.
Table 4. LKCT[1:0] Programming
LKCT[1:0]
0
1
2
3
COUNTS
32
128
512
2048
When the PFD phase difference is greater than tLWW , the
lock indicator immediately asserts the UNLOCK status
flag and clears the LOCK flag, indicating an out-of-lock
condition. The UNLOCK flag is immediately de-asserted
when the phase difference is less than tLWW . See Figure 4
for more details.
+tLWW
PHASE
DIFFERENCE
AT PFD
0
–tLWW
UNLOCK FLAG
LOCK FLAG
t = COUNTS/fPFD
Figure 4. UNLOCK and LOCK Timing
For more information www.linear.com/LTC6945
6945 F04
6945fa
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11 Page | ||
| Páginas | Total 28 Páginas | |
| PDF Descargar | [ Datasheet LTC6945.PDF ] | |
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