FeaTures
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LTC6945
Ultralow Noise and Spurious
0.35GHz to 6GHz Integer-N
Synthesizer
DescripTion
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.
Low Noise Integer-N PLL
350MHz to 6GHz VCO Input Range
–226dBc/Hz Normalized In-Band Phase Noise Floor
–274dBc/Hz Normalized In-Band 1/f Noise
–157dBc/Hz Wideband Output Phase Noise Floor
Excellent Spurious Performance
Output Divider (1 to 6, 50% Duty Cycle)
Low Noise Reference Buffer
Output Buffer Muting
Charge Pump Supply from 3.15V to 5.25V
Charge Pump Current from 250µA to 11.2mA
Configurable Status Output
SPI Compatible Serial Port Control
PLLWizard™ Software Design Tool Support
applicaTions
n
n
n
n
n
Wireless Base Stations (LTE, WiMAX, W-CDMA, PCS)
Broadband Wireless Access
Microwave Data Links
Military and Secure Radio
Test and Measurement
Typical applicaTion
LTC6945 Data Converter Sample Clock
LOOP
3.3V
BANDWIDTH
0.1µF
~2.3kHz
51.1
1µF
REF
–
REF
+
V
REF+
CP V
CP+
GND
V
REFO+
V
VCO+
REFO
STAT
CS
SPI BUS
SCLK
SDI
SDO
3.3V
0.1µF
f
PFD
= 25MHz
LTC6945
GND
GND
GND
GND
GND
GND
V
CO+
100pF
1.0µF
16.5
100pF
16.5
3.3V 0.01µF
PHASE NOISE (dBc/Hz)
5V
0.1µF
432
570nF
V
TUNE
47nF
5V
CRYSTEK
CVCSO-914-1000
1GHz Sample Clock Phase Noise
–100
–110
–120
–130
–140
–150
–160
–170
–180
100
1k
1M
10k
100k
OFFSET FREQUENCY (Hz)
10M 40M
6945 TA01b
100MHz
REF
1µF
3.3V
0.1µF
DSB INTEGRATION
(100Hz TO 1GHz)
RMS NOISE = 0.014°
RMS JITTER = 39fs
f
PFD
= 25MHz
BW = 2.3kHz
V
D+
V
CO–
MUTE
GND RF
–
RF
+
V
RF+
BB
68nH
100pF
50
68nH
16.5
100pF
SAMPLE CLOCK
1GHz, 7dBm
6945 TA01b
3.3V
3.3V 0.01µF
3.3V
100pF
ALT SAMPLE CLOCK
500MHz OR 1GHz
6945fa
For more information
www.linear.com/LTC6945
1
LTC6945
absoluTe MaxiMuM raTings
(Note 1)
pin conFiguraTion
TOP VIEW
V
REF+
REF
–
REF
+
V
CP+
+
Supply Voltages
V
+
(V
REF+
, V
REFO+
, V
RF+
, V
VCO+
, V
D+
) to GND ......3.6V
V
CP+
to GND.........................................................5.5V
Voltage on CP Pin .................GND – 0.3V to V
CP+
+ 0.3V
Voltage on All Other Pins ..........GND – 0.3V to V
+
+ 0.3V
Operating Junction Temperature Range, T
J
(Note 2)
LTC6945I ............................................... –40°C to 105°C
Junction Temperature, T
JMAX
................................ 125°C
Storage Temperature Range .................. –65°C to 150°C
28 27 26 25 24 23
V
REFO
+ 1
REFO 2
STAT 3
CS
4
SCLK 5
SDI 6
SDO 7
V
D+
8
9 10 11 12 13 14
MUTE
GND
RF
–
RF
+
V
RF
BB
29
GND
22 V
VCO+
21 GND
20 GND
19 GND
18 GND
17 GND
16 VCO
+
15 VCO
–
UFD PACKAGE
28-LEAD (4mm
×
5mm) PLASTIC QFN
T
JMAX
= 125°C,
θ
JCbottom
= 3°C/W,
θ
JCtop
= 26°C/W
EXPOSED PAD (PIN 29) IS GND, MUST BE SOLDERED TO PCB
orDer inForMaTion
LEAD FREE FINISH
LTC6945IUFD#PBF
TAPE AND REEL
LTC6945IUFD#TRPBF
PART MARKING
6945
PACKAGE DESCRIPTION
28-Lead (4mm
×
5mm) Plastic QFN
JUNCTION TEMPERATURE RANGE
–40°C to 105°C
Consult LTC Marketing for parts specified with wider operating temperature ranges.
Consult LTC Marketing for information on non-standard lead based finish parts.
For more information on lead free part marking, go to:
http://www.linear.com/leadfree/
For more information on tape and reel specifications, go to:
http://www.linear.com/tapeandreel/
elecTrical characTerisTics
SYMBOL
f
REF
V
REF
PARAMETER
Input Frequency
Input Signal Level
Input Slew Rate
Input Duty Cycle
Self-Bias Voltage
Input Resistance
Input Capacitance
Reference Output (REFO)
f
REFO
P
REFO
Output Frequency
Output Power
Output Impedance, Disabled
Reference Inputs (REF
+
, REF
–
)
The
l
denotes the specifications which apply over the full operating
junction temperature range, otherwise specifications are at T
A
= 25°C. V
REF+
= V
REF0+
= V
D+
= V
RF+
= V
VCO+
= 3.3V, V
CP+
= 5V unless
otherwise specified. All voltages are with respect to GND.
CONDITIONS
l
MIN
10
0.5
20
GND
CP
TYP
MAX
250
UNITS
MHz
V
P-P
V/µs
%
Single-Ended, 1µF AC-Coupling Capacitors
l
l
2
50
2.7
l
1.65
6.2
1.85
8.4
3
2.25
11.6
V
kΩ
pF
Differential
Differential
l
l
10
–0.2
800
250
3.2
MHz
dBm
Ω
6945fa
f
REFO
= 10MHz, R
LOAD
= 50Ω
l
2
For more information
www.linear.com/LTC6945
LTC6945
elecTrical characTerisTics
SYMBOL
f
VCO
P
VCOI
PARAMETER
Input Frequency
Input Power Level
Input Resistance
RF Output (RF
+
, RF
–
)
f
RF
O
Output Frequency
Output Divider Range
Output Duty Cycle
Output Resistance
Output Common Mode Voltage
P
RF(SE)
Output Power, Single-Ended,
f
RF
= 900MHz
Output Power, Muted
Mute Enable Time
Mute Disable Time
Phase/Frequency Detector
f
PFD
t
LWW
Input Frequency
Lock Window Width
LKWIN[1:0] = 0
LKWIN[1:0] = 1
LKWIN[1:0] = 2
LKWIN[1:0] = 3
Increase in t
LWW
Moving from Locked State to
Unlocked State
12 Settings (See Table 5)
V
CP
= V
CP+
/2, All Settings
I
CP
= 250µA to 1.4mA, V
CP
= V
CP+
/2
I
CP
= 2mA to 11.2mA, V
CP
= V
CP+
/2
(Note 3)
V
CP
= V
CP+
/2
I
CP
= 700µA, CPCLO = CPCHI = 0 (Note 3)
I
CP
= 11.2mA, CPCLO = CPCHI = 0 (Note 3)
CPCLO = 1
CPCHI = 1, Referred to V
CP+
Referred to (V
CP+
– GND)
All Integers Included
l
l
l
l
l
The
l
denotes the specifications which apply over the full operating
junction temperature range, otherwise specifications are at T
A
= 25°C. V
REF+
= V
REF0+
= V
D+
= V
RF+
= V
VCO+
= 3.3V, V
CP+
= 5V unless
otherwise specified. All voltages are with respect to GND.
CONDITIONS
l
MIN
350
–8
97
350
1
TYP
MAX
6000
UNITS
MHz
dBm
Ω
MHz
%
VCO Input (VCO
+
, VCO
–
)
R
Z
= 50Ω, Single-Ended
Single-Ended, Each Input
l
l
0
121
6
145
6000
6
All Integers Included
Single-Ended, Each Output to V
RF+
RFO[1:0] = 0, R
Z
= 50Ω, LC Match
RFO[1:0] = 1, R
Z
= 50Ω, LC Match
RFO[1:0] = 2, R
Z
= 50Ω, LC Match
RFO[1:0] = 3, R
Z
= 50Ω, LC Match
R
Z
= 50Ω, Single-Ended, f
RF
= 900MHz, O = 2 to 6
l
50
l
l
l
l
l
l
l
l
l
111
2.4
–9.7
–6.8
–3.9
–1.2
136
159
V
RF+
–6.0
–3.6
–0.4
2.3
–60
110
170
100
Ω
V
dBm
dBm
dBm
dBm
dBm
ns
ns
MHz
ns
ns
ns
ns
%
Lock Indicator, Available on the STAT Pin and via the SPI-Accessible Status Register
3.0
10.0
30.0
90.0
22
t
LWHYS
Charge Pump
I
CP
Lock Window Hysteresis
Output Current Range
Output Current Source/Sink Accuracy
Output Current Source/Sink Matching
Output Current vs Output Voltage
Sensitivity
Output Current vs Temperature
Output Hi-Z Leakage Current
0.25
11.2
±6
±3.5
±2
0.1
170
0.5
5
0.84
–0.96
0.48
1.0
mA
%
%
%
%/V
ppm/°C
nA
nA
V
V
V/V
V
CLMP(LO)
V
CLMP(HI)
V
MID
R
Low Clamp Voltage
High Clamp Voltage
Mid-Supply Output Bias Ratio
Divide Range
Reference (R) Divider
1
1023
Counts
6945fa
For more information
www.linear.com/LTC6945
3
LTC6945
elecTrical characTerisTics
SYMBOL
N
V
IH
V
IL
V
IHYS
I
OH
I
OL
PARAMETER
Divide Range
High Level Input Voltage
Low Level Input Voltage
Input Voltage Hysteresis
Input Current
High Level Output Current
Low Level Output Current
SDO Hi-Z Current
Digital Timing Specifications (See Figures 8 and 9)
t
CKH
t
CKL
t
CSS
t
CSH
t
CS
t
CH
t
DO
SCLK High Time
SCLK Low Time
CS
Setup Time
CS
High Time
SDI to SCLK Setup Time
SDI to SCLK Hold Time
SCLK to SDO Time
V
REF+
Supply Range
V
REFO
V
D
+
Supply Range
+
Supply Range
The
l
denotes the specifications which apply over the full operating
junction temperature range, otherwise specifications are at T
A
= 25°C. V
REF+
= V
REF0+
= V
D+
= V
RF+
= V
VCO+
= 3.3V, V
CP+
= 5V unless
otherwise specified. All voltages are with respect to GND.
CONDITIONS
All Integers Included
MUTE, CS,
SDI, SCLK
MUTE, CS,
SDI, SCLK
MUTE, CS,
SDI, SCLK
MUTE, CS,
SDI, SCLK
SDO and STAT, V
OH
= V
D
+
– 400mV
MIN
l
TYP
MAX
65535
UNITS
Counts
V
VCO (N) Divider
32
1.55
0.8
250
l
l
l
l
Digital Pin Specifications
l
l
V
mV
µA
mA
mA
µA
ns
ns
ns
ns
ns
ns
±1
–2.3
1.8
3.4
±1
25
25
10
10
6
6
16
3.15
3.15
3.15
3.15
3.15
3.15
3.3
3.3
3.3
3.3
3.3
3.45
3.45
3.45
3.45
3.45
5.25
500
34
12
235
7.8
70
79
88
105
111
116
202
39
14.5
385
9.0
78
88
98
117
124
128
396
–1.4
SDO and STAT, V
OL
= 400mV
l
l
l
l
l
l
To V
IH
/V
IL
/Hi-Z with 30pF Load
l
ns
V
V
V
V
V
V
µA
mA
mA
µA
mA
mA
mA
mA
mA
mA
mA
µA
Power Supply Voltages
l
l
l
l
l
l
V
RF+
Supply Range
V
VCO+
Supply Range
V
CP+
Supply Range
Power Supply Currents
I
DD
I
CC(CP)
I
CC(REFO)
I
CC
V
D+
Supply Current
V
CP+
Supply Current
V
REFO+
Supply Currents
Sum V
REF+
, V
RF+
, V
VCO+
Supply
Currents
Digital Inputs at Supply Levels
I
CP
= 11.2mA
I
CP
= 1.0mA
PDALL = 1
REFO Enabled, R
Z
=
∞
RF Muted, OD[2:0] = 1
RF Enabled, RFO[1:0] =0, OD[2:0] = 1
RF Enabled, RFO[1:0] = 3, OD[2:0] = 1
RF Enabled, RFO[1:0] =3, OD[2:0] = 2
RF Enabled, RFO[1:0] =3, OD[2:0] = 3
RF Enabled, RFO[1:0] =3, OD[2:0] = 4 to 6
PDALL = 1
l
l
l
l
l
l
l
l
l
l
l
l
4
6945fa
For more information
www.linear.com/LTC6945
LTC6945
elecTrical characTerisTics
SYMBOL
L
M(MIN)
PARAMETER
Output Phase Noise Floor (Note 5)
Phase Noise and Spurious
RFO[1:0] = 3, OD[2:0] = 1, f
RF
= 6GHz
RFO[1:0] = 3, OD[2:0] = 2, f
RF
= 3GHz
RFO[1:0] = 3, OD[2:0] = 3, f
RF
= 2GHz
RFO[1:0] = 3, OD[2:0] = 4, f
RF
= 1.5GHz
RFO[1:0] = 3, OD[2:0] = 5, f
RF
= 1.2GHz
RFO[1:0] = 3, OD[2:0] = 6, f
RF
= 1.0GHz
I
CP
= 11.2mA (Notes 6, 7, 8)
I
CP
= 11.2mA (Notes 6, 9)
(Notes 6, 7, 8, 10)
(Notes 4, 7, 10)
Reference Spur, PLL locked (Notes 4, 7, 10, 11)
–155
–155
–156
–156
–157
–158
–226
–274
–99
0.13
–102
dBc/Hz
dBc/Hz
dBc/Hz
dBc/Hz
dBc/Hz
dBc/Hz
dBc/Hz
dBc/Hz
dBc/Hz
°RMS
dBc
The
l
denotes the specifications which apply over the full operating
junction temperature range, otherwise specifications are at T
A
= 25°C. V
REF+
= V
REF0+
= V
D+
= V
RF+
= V
VCO+
= 3.3V, V
CP+
= 5V unless
otherwise specified. All voltages are with respect to GND.
CONDITIONS
MIN
TYP
MAX
UNITS
L
M(NORM)
L
M(IB)
Normalized In-Band Phase Noise Floor
In-Band Phase Noise Floor
Integrated Phase Noise from 100Hz to
40MHz
Spurious
L
M(NORM –1/f)
Normalized In-Band 1/f Phase Noise
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 ≤ V
CP
≤ (V
CP+
– 0.9V).
Note 4:
VCO is Crystek CVCO55CL-0902-0928.
Note 5:
f
VCO
= 6GHz, f
OFFSET
= 40MHz.
Note 6:
Measured inside the loop bandwidth with the loop locked.
Note 7:
Reference frequency supplied by Wenzel 501-04608A,
f
REF
= 10MHz, P
REF
= 13dBm.
Note 8:
Output phase noise floor is calculated from normalized phase
noise floor by L
M(OUT)
= –226 + 10log
10
(f
PFD
) + 20log
10
(f
RF
/f
PFD
).
Note 9:
Output 1/f phase noise is calculated from normalized 1/f phase
noise by L
M(OUT –1/f)
= –274 + 20log
10
(f
RF
) – 10log
10
(f
OFFSET
).
Note 10:
I
CP
= 11.2mA, f
PFD
= 250kHz, f
RF
= 914MHz, FILT[1:0] = 3, Loop
BW = 7kHz.
Note 11:
Measured using DC1649.
Typical perForMance characTerisTics
REF Input Sensitivity vs
Frequency
–15
–20
SENSITIVITY (dBm)
–25
–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
BST = 1
FILT = 0
T
J
= 105°C
T
J
= 25°C
T
J
= –40°C
P
OUT
(dBm)
4
3
2
1
0
–1
–2
–3
–4
0
25 50 75 100 125 150 175 200 225 250
FREQUENCY (MHz)
6945 G02
REFO Phase Noise
–140
P
OUT
= 1.45dBm
f
REF
= 10MHz
BST = 1
FILT = 3
NOTE 7
T
J
= 105°C
T
J
= 25°C
T
J
= –40°C
PHASE NOISE (dBc/Hz)
–145
–150
–155
–160
100
10k
100k
1M
1k
OFFSET FREQUENCY (Hz)
5M
6945 G03
6945fa
For more information
www.linear.com/LTC6945
5
嵌入式系统
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