LMX2370/LMX2371/LMX2372
PLLatinum™ Dual Frequency Synthesizer for RF
Personal Communications
LMX2370
LMX2371
LMX2372
The LMX237x are available in a 24-pad chip scale (CSP) or
a 20-pin TSSOP surface mount plastic package.
2.5 GHz/1.2 GHz
2.0 GHz/1.2 GHz
1.2 GHz/1.2 GHz
Features
General Description
The LMX237x family of monolithic, integrated dual frequency
synthesizers, including prescalers, is designed to be used as
a first and second local oscillator for dual mode or dual conversion transceivers. It is fabricated using National’s 0.5u
ABiCV silicon BiCMOS process. The LMX237x contains two
dual modulus prescalers. A 32/33 or a 16/17 prescaler can
be selected for the 2.5 GHz and 2.0 GHz RF synthesizers
with the 16/17 prescaler rated for input frequencies below
1.2 GHz. A 16/17 or an 8/9 prescaler can be selected for the
1.2 GHz RF synthesizers with the 8/9 prescaler rated for input frequencies below 550 MHz. Using a digital phase
locked loop technique, the LMX237x can generate very
stable, low noise control signals for UHF and VHF voltage
controlled oscillators (VCOs). Serial data is transferred into
the LMX237x via a 1.8 V three wire interface (Data, Enable,
Clock) compatible with low voltage baseband processors.
Supply voltage can range from 2.7V to 5.5V. The LMX237x
family features very low current consumption typically:
LMX2370 - 6.0 mA at 3V, LMX2371 - 5.0 mA at 3V, LMX2372
- 4.0 mA at 3V.
n
n
n
n
n
n
n
n
n
2.7V–5.5V operation
Ultra low current consumption
Low phase detector noise floor
Low voltage MICROWIRE™ interface (1.8V up to VCC)
Low prescaler values
32/33 at fIN ≤ 2.5 GHz
16/17 at fIN ≤ 1.2 GHz
8/9 at fIN ≤ 550 MHz
Selectable charge pump current levels
Selectable FastLock™ mode
Enhanced ESD protection
Available in small 24-pad chip scale package (3.5 x 4.5
x 1.0 mm)
Applications
n
n
n
n
Portable wireless communications (PCS/PCN, cordless)
Dual mode cellular telephone systems
Spread spectrum communication systems (CDMA)
Cable TV tuners (CATV)
Functional Block Diagram
DS101026-4
FastLock™, PLLatinum™ and MICROWIRE™ are trademarks of National Semiconductor Corporation.
TRI-STATE ® is a registered trademark of National Semiconductor Corporation.
© 2000 National Semiconductor Corporation
DS101026
www.national.com
LMX2370/LMX2371/LMX2372 PLLatinum Dual Frequency Synthesizer for RF Personal
Communications
July 2000
LMX2370/LMX2371/LMX2372
Connection Diagrams
TSSOP 20-Pin Package
CSP 24-Pin Package
DS101026-2
Top View
Order Number LMX2370TM, LMX2370TMX,
LMX2371TM, LMX2371TMX,
LMX2372TM or LMX2372TMX
See NS Package Number MTC20
DS101026-3
Top View
Order Number LMX2370SLBX,
LMX2371SLBX or LMX2372SLBX
See NS Package Number SLB24A
Pin Descriptions
Pin No.
Pin
Name
I/O
Description
1
VCC1
—
Power supply voltage input for RF analog and
RF digital circuits. Input may range from 2.7V to
5.5V. VCC1 must equal VCC2. Bypass capacitors
should be placed as close as possible to this pin
and be connected directly to the ground plane.
2
2
Vp1
—
Power supply for Main charge pump. Must be ≥
VCC.
3
3
CPo1
O
Internal Main charge pump output. For
connection to a loop filter for driving the input of
an external VCO.
4
4
GND
—
Ground for Main digital circuitry.
5
5
fIN1
I
Main prescaler input. Small signal input from the
VCO.
6
6
fIN1b
I
Main prescaler complementary input. For single
ended operation, a bypass capacitor should be
placed as close as possible to this pin and be
connected directly to the ground plane.
7
7
GND
—
24-Pin
CSP
20-Pin
TSSOP
24
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Ground for Main analog circuitry.
2
Pin No.
(Continued)
Pin
Name
I/O
8
OSCin
I
10
9
GND
—
Ground for Aux digital, MICROWIRE, FoLD, and
oscillator circuits.
11
10
Fo/LD
O
Multiplexed output of the Main/Aux
programmable or reference dividers,
Main/Auxiliary lock detect signals and Fastlock
mode. CMOS output (see Programmable Modes
in the Datasheet).
12
11
Clock
I
High impedance CMOS Clock input. Data for the
various counters is clocked in on the rising edge,
into the 22-bit shift register.
14
12
Data
I
Binary serial data input. Data entered MSB first.
The last two bits are the control bits. High
impedance CMOS input.
15
13
LE
I
Load enable. High impedance CMOS input.
When LE goes HIGH, data stored in the shift
registers is loaded into one of the 4 appropriate
latches (control bit dependent).
16
14
Vµc
—
Power supply for MICROWIRE circuitry. Must be
≤ VCC. Typically connected to same supply level
as µprocessor or baseband controller to enable
programming at low voltages.
17
15
GND
—
Ground for Aux analog circuitry.
18
16
fIN2
I
Auxiliary prescaler input. Small signal input from
the VCO.
19
17
GND
—
Ground for Aux digital, MICROWIRE, FoLD, and
oscillator.
20
18
CPo2
O
Aux internal charge pump output. For connection
to a loop filter for driving the input of an external
VCO.
22
19
Vp2
—
Power supply for Aux charge pump. Must be ≥
VCC.
24-Pin
CSP
20-Pin
TSSOP
8
LMX2370/LMX2371/LMX2372
Pin Descriptions
Description
Oscillator input. The input has a VCC/2 input
threshold and can be driven from an external
CMOS or TTL logic gate.
3
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LMX2370/LMX2371/LMX2372
Pin Descriptions
Pin No.
(Continued)
Pin
Name
I/O
Description
20
VCC2
—
Power supply voltage input for Aux analog, Aux
digital, FoLD, and oscillator circuits. Input may
range from 2.7V to 5.5V. VCC2 must equal VCC1.
Bypass capacitors should be placed as close as
possible to this pin and be connected directly to
the ground plane.
—
NC
—
No Connect
24-Pin
CSP
20-Pin
TSSOP
23
1, 9,
13, 21
Block Diagram (Note 1)
DS101026-8
Note 1: * The numbers in () represent the equivalent chipscale package (CSP) pinout
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4
Recommended Operating
Conditions (Note 4)
If Military/Aerospace specified devices are required,
please contact the National Semiconductor Sales Office/
Distributors for availability and specifications.
Power Supply Voltage
VCC1
VCC2
VCC1–VCC2
Vp1
Vp2
Vµc
Operating Temperature (TA)
Power Supply Voltage
VCC1
−0.3V to 6.5V
−0.3V to 6.5V
VCC2
Vp1
−0.3V to 6.5V
Vp2
−0.3V to 6.5V
Vµc
−0.3V to 6.5V
Voltage on any pin with
−0.3V to VCC +0.3V
GND = 0V (VI)
−65˚C to +150˚C
Storage Temperature Range (TS)
+260˚C
Lead Temperature (solder, 4 sec.) (TL)
< 2 keV
ESD - Human Body Model (Note 3)
2.7V to 5.5V
2.7V to 5.5V
−0.2V to 0.2V
VCC to 5.5V
VCC to 5.5V
1.72V to VCC
−40˚C to +85˚C
Note 2: Absolute Maximum Ratings indicate limits beyond which damage to
the device may occur. Operating Ratings indicate conditions for which the device is intended to be functional, but do not guarantee specific performance
limits. For guaranteed specifications and test conditions, see the Electrical
Characteristics. The guaranteed specifications apply only for the test conditions listed.
Note 3: This device is a high performance RF integrated circuit and is ESD
sensitive. Handling and assembly of this device should only be done at ESD
free workstations.
Note 4: VCC is defined as VCC = VCC1 = VCC2.
Electrical Characteristics
(VCC = Vp = Vµc = 3.0V; −40˚C < TA < 85˚C except as specified).
GENERAL
Value
Symbol
ICC
Parameter
Power Supply
Current
Conditions
Unit
Main = On, Aux = On
6
8.5
mA
Main = On, Aux = On
5
7.5
mA
LMX2372
Main = On, Aux = On
4
6.0
mA
LMX2370
/71/72
Aux Only
2
3.25
mA
Power Down Current
EN_Main, EN_Aux = 0
Main PLL
Operating
Frequency
P = 32/33
LMX2370
LMX2371
LMX2372
Auxiliary PLL Operating
Frequency
fφ
Phase Detector Frequency
PfIN1, PfIN2
RF Input Sensitivity
50
µA
1.2
15
2.5
GHz
P = 16/17
45
1200
MHz
P = 32/33
1.2
2.0
GHz
P = 16/17
45
1200
MHz
P = 16/17
45
1200
MHz
P = 8/9
45
550
MHz
P = 16/17
45
1200
MHz
P = 8/9
45
550
MHz
10
MHz
2.7 ≤ VCC ≤ 3.6V
−15
0
dBm
3.6 ≤ VCC ≤ 5.5V
−10
0
dBm
OSCILLATOR INPUT
Value
Parameter
OSCin
Reference Oscillator Input
Operating Frequency
Conditions
VOSC
Oscillator Input Sensitivity
OSCin
IIH
OSCin Input Current
VIH = VCC = 5.5V
IIL
OSCin Input Current
VIL = 0, VCC = 5.5V
Min
Typ
Max
50
MHz
0.5
VCC
VPP
100
µA
−100
µA
Value
Parameter
Min
Typ
Max
Unit
VCPo = Vp/2, ICPo_4X = 0
- 1.0
mA
VCPo = Vp/2, ICPo_4X = 0
1.0
mA
ICPo-source
VCPo = Vp/2, ICPo_4X = 1
- 4.0
mA
ICPo-sink
VCPo = Vp/2, ICPo_4X = 1
4.0
mA
ICPo-source
ICPo-sink
Main and Auxiliary Charge
Pump Output Current (Note 5)
Conditions
Unit
2
CHARGE PUMP
Symbol
Max
LMX2371
fIN1
Symbol
Typ
LMX2370
ICC-PWDN
fIN2
Min
5
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LMX2370/LMX2371/LMX2372
Absolute Maximum Ratings (Notes 2, 3)
LMX2370/LMX2371/LMX2372
Electrical Characteristics
(VCC = Vp = Vµc = 3.0V; −40˚C < TA < 85˚C except as specified). (Continued)
CHARGE PUMP
Symbol
Value
Parameter
Min
Typ
Max
−2.5
0.1
2.5
nA
3
10
%
8
15
%
ICPo-TRI
Charge Pump TRI-STATE ®
Current
0.5 ≤ VCPo ≤ Vp − 0.5,
−40˚C < TA < 85˚C
ICPo-sink vs
ICPo-source
CP Sink vs Source Mismatch
VCPo = Vp/2, TA = 25˚C
ICPo vs
VCPo
CP Current vs Voltage
0.5 ≤ VCPo ≤ Vp − 0.5, TA = 25˚C
ICPo vs TA
CP Current vs Temperature
VCPo = Vp/2, −40˚C < TA < 85˚C
8
DIGITAL INTERFACE (DATA, CLOCK, LE)
Symbol
Parameter
%
Value
Conditions
Min
VIH
High-Level Input Voltage
Vµc = 1.72V to 5.5V
VIL
Low-Level Input Voltage
Vµc = 1.72V to 5.5V
IIH
High-Level Input Current
VIH = Vµc = 5.5V
−1.0
IIL
Low-Level Input Current
VIL = 0, Vµc = 5.5V
−1.0
VOL
Low-Level Output Current
IOL = 1.0 mA, VEXT = 1.8V (Note
6)
Typ
Max
0.8 Vµc
0.2 Vµc
V
1.0
µA
1.0
µA
0.4
V
Value
Parameter
Conditions
Min
Unit
V
0.1
MICROWIRE TIMING
Symbol
Unit
Conditions
Typ
Max
Unit
tCS
Data to Clock Setup Time
See Data Input Timing
50
ns
tCH
Data to Clock Hold Time
See Data Input Timing
20
ns
tCWH
Clock Pulse Width High
See Data Input Timing
50
ns
tCWL
Clock Pulse Width Low
See Data Input Timing
50
ns
tES
Clock to Load Enable Setup
Time
See Data Input Timing
50
ns
tEW
Load Enable Pulse Width
See Data Input Timing
50
ns
Note 5: Main and Auxiliary Charge Pump magnitude are controlled by Main_ICPo_4X and Aux_ICPo_4X bits respectively.
Note 6: Lock Detect open drain output only pulled up to VEXT. Typically VEXT = VCC.
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6
LMX2370/LMX2371/LMX2372
Charge Pump Current Specification Definitions
DS101026-19
I1 = CP sink current at VDo = VP − ∆V
I2 = CP sink current at VDo = VP/2
I3 = CP sink current at VDo = ∆V
I4 = CP source current at VDo = VP − ∆V
I5 = CP source current at VDo = VP/2
I6 = CP source current at VDo = ∆V
∆V = Voltage offset from positive and negative rails. Dependent on VCO tuning range relative to VCC and ground. Typical values are between 0.5V and 1.0V.
1. IDo vs VDo = Charge Pump Output Current magnitude variation vs Voltage =
[1⁄2 * {|I1| − |I3|}]/[1⁄2 * {|I1| + |I3|}] * 100% and [1⁄2 * {|I4| − |I6|}]/[1⁄2 * {|I4| + |I6|}] * 100%
2. IDo-sink vs IDo-source = Charge Pump Output Current Sink vs Source Mismatch =
[|I2| − |I5|]/[1⁄2 * {|I2| + |I5|}] * 100%
3. IDo vs TA = Charge Pump Output Current magnitude variation vs Temperature =
[|I2 @ temp| − |I2 @ 25˚C|]/|I2 @ 25˚C| * 100% and [|I5 @ temp| − |I5 @ 25˚C|]/|I5 @ 25˚C| * 100%
RF Sensitivity Test Block Diagram
DS101026-20
Note: N = 10,000
R = 50
P = 64
Note: Sensitivity limit is reached when the error of the divided RF output, FoLD, is ≥ 1 Hz.
7
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LMX2370/LMX2371/LMX2372
Typical Performance Characteristics
ICC vs VCC
LMX2370
ICC vs VCC
LMX2371
DS101026-21
ICC vs VCC
LMX2372
DS101026-22
ICPo TRI-STATE
vs CPO Voltage
DS101026-24
DS101026-23
Charge Pump Current vs CPO Voltage
ICPO = HIGH
Charge Pump Current vs CPO Voltage
ICPO = LOW
DS101026-25
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DS101026-26
8
(Continued)
Sink vs Source 1x-Mode Mismatch
(See Note 2 under Charge Pump Current Specification
Definitions)
Sink vs Source 4x-Mode Mismatch
(See Note 2 under Charge Pump Current Specification
Definitions)
DS101026-27
RF Input Impedance, T = 25˚C
VCC = 2.7V to 5.5V, fIN1 = 30 kHz to 3 GHz
DS101026-28
AUX Input Impedance, T = 25˚C
VCC = 2.7V to 5.5V, fIN2 = 10 MHz to 1000 MHz
DS101026-29
Marker
Marker
Marker
Marker
1
2
3
4
=
=
=
=
500 MHz, Real = 21.602, Imag. = −84.160
1 GHz, Real = 9.2314, Imag. = −28.793
2 GHz, Real = 9.9365, Imag. = 27.582
2.5 GHz, Real = 25.867, Imag. = 71.137
DS101026-30
Marker 1 = 500 MHz, Real = 21.836, Imag. = −85.836
Marker 2 = 750 MHz, Real = 12.824, Imag. = −50.973
Marker 3 = 1 GHz, Real = 9.6270, Imag. = −29.989
9
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LMX2370/LMX2371/LMX2372
Typical Performance Characteristics
LMX2370/LMX2371/LMX2372
Typical Performance Characteristics
(Continued)
LMX2370 RF Sensitivity vs Frequency
LMX2371 RF Input Sensitivity vs Frequency
DS101026-32
DS101026-31
LMX2372 RF Sensitivity vs Frequency
Auxiliary Input Sensitivity vs Frequency
DS101026-33
DS101026-34
Oscillator Input Sensitivity vs Frequency
DS101026-35
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10
The basic phase-lock-loop (PLL) configuration consists of a high-stability crystal reference oscillator, a frequency synthesizer
such as the National Semiconductor LMX2370/2371/2372, a voltage controlled oscillator (VCO), and a passive loop filter. The frequency synthesizer includes a phase detector, a current mode charge pump, as well as programmable reference [R] and feedback [N] frequency dividers. The VCO frequency is established by dividing the crystal reference signal down via the R-counter to
obtain a comparison reference frequency. This reference signal (fR) is then presented to the input of a phase/frequency detector
and compared with the feedback signal (fN), which is obtained by dividing the VCO frequency down by way of the N-counter. The
phase/frequency detector’s current source output pumps charge into the loop filter, which then integrates into the VCO’s control
voltage. The function of the phase/frequency comparator is to adjust the control voltage presented to the VCO until the feedback
signal frequency and phase match that of the reference signal. When this “Phase-Locked” condition exists, the VCO frequency
will be N times that of the comparison frequency, where N is the integer divide ratio.
1.1 REFERENCE OSCILLATOR INPUT
The reference oscillator frequency for the Main and Auxiliary PLLs is provided from the external reference through the OSCin pin.
OSCin can operate up to 50 MHz with input sensitivity of 0.5 VPP. The OSCin pin drives both the Main R-counter and the Auxiliary
R-counter. The input has a VCC/2 input threshold that can be driven from an external CMOS or TTL logic gate. Typically, the OSCin
is connected to the output of a crystal oscillator.
1.2 REFERENCE DIVIDERS (R-COUNTERS)
The Main and Auxiliary R-counters are both clocked through the oscillator block in common. The maximum frequency is 50 MHz.
Both R-counters are CMOS design and 15-bit in length with programmable divider ratio from 2 to 32,767.
1.3 PRESCALERS
The complimentary fIN and fINB inputs drive a differential-pair amplifier which feeds to the respective prescaler. The Main PLL
complementary fIN1 and fIN1b inputs can be driven differentially, or the negative input can be AC coupled to ground through an
external capacitor for single ended configuration. The Auxiliary PLL has the complimentary input AC coupled to ground through
an internal 10 pF capacitor. The Auxilllary PLL complimentary input is not brought out to a pin, and is intended for single ended
configuration only. The LMX237x has a dual modulus prescaler with 2 selectable modulo. For PLL’s rated at 2.5 GHz or 2.0 GHz
a 32/33 or 16/17 prescaler is available. For PLL’s rated at 1.2 GHz a 16/17 or 8/9 can be chosen. Both Main and Auxiliary prescalers’ outputs drive the subsequent CMOS flip-flop chain comprising the programmable N feedback counters. The proper prescaler value must be chosen to in order not to exceed the maximum CMOS frequency. For fIN > 1.2 GHz, the 32/33 prescaler must
be selected, similarly for fIN > 550 MHz, the prescaler value must be at least 16/17, and for fIN < 550 MHz, an 8/9 prescaler value
is allowable.
1.4 FEEDBACK DIVIDERS (N-COUNTERS)
The Main and Auxiliary N-counters are clocked by the output of Main and Aux prescalers respectively. The N-counter is composed
of a 13-bit integer divider and a 5-bit swallow counter. Selecting a 32/33 prescaler provides a minimum continuous divider range
from 992 to 262,143 while selecting a 16/17 or 8/9 prescaler value allows for continuous divider values between and 240 to
131,087 and 56 to 65,559 respectively.
1.5 PHASE/FREQUENCY DETECTORS
The phase/frequency detectors are driven from their respective N- and R-counter outputs. The maximum frequency at the phase
detector inputs is 10 MHz unless limited by the minimum continuous divide ratio of the dual-modulus prescaler. The phase detector output controls the charge pump. The polarity of the pump-up or pump-down control is programmed using Main_PD_POL
or Aux_PD_POL, depending on whether Main or Auxiliary VCO characteristics is positive or negative. The phase detector also
receives a feedback signal from the charge pump in order to eliminate dead zone.
1.6 CHARGE PUMPS
The phase detector’s current source output pumps charge into an external loop filter, which then integrates into the VCO’s control
voltage. The charge pump steers the charge pump output CPo to VP (pump-up) or Ground (pump-down). When locked, CPo is
primarily in a TRI-STATE mode with small corrections. The charge pump output current magnitude can be selected as 1.0 mA or
4.0 mA by programming the Main_ICPo_4X or Aux_ICPo_4X bits.
1.7 MICROWIRE SERIAL INTERFACE
The programmable register set is accessed through the Microwire serial interface. The interface is comprised of three signal pins:
clock, data and load enable (LE). The supply for the MICROWIRE circuitry is separate from the rest of the IC to allow for controller
voltages down to 1.8V. Serial data is clocked into the 22-bit shift register upon the rising edge of clock. The MSB bit of data shifts
first. The last two bits decode the internal register address. On the rising edge of LE, data stored in the shift register is loaded into
one of the four latches according to the address bits. The synthesizer can be programmed even in power down state. A complete
programming description is followed in Section 2.0.
1.8 MULTIFUNCTION OUTPUTS
The LMX2370/LMX2371/LMX2372 FoLD output pin can be configured as the FastLock output or CMOS programmed output,
analog lock detects as well as showing the internal block status such as the counter outputs.
11
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LMX2370/LMX2371/LMX2372
1.0 Functional Description
LMX2370/LMX2371/LMX2372
1.0 Functional Description
(Continued)
1.8.1 Lock Detect Output
An analog lock detect status generated from the phase detector is available on the Fo/LD output pin, if selected. The lock detect
output goes high when the charge pump is inactive. It goes low when the charge pump is active during a comparison cycle. The
lock detect signal output is an open drain configuration. When a PLL is in power down mode, the respective lock detect output
is always high.
1.8.2 FastLock Outputs
When configured as FastLock mode, the current can be increased 4x while maintaining loop stability by synchronously switching
a parallel loop filter resistor to ground, resulting in a ∼2x change in loop bandwidth. The zero gain crossover point of the open loop
gain, or the loop bandwidth is effectively shifted up in frequency by a factor of √4 = 2 during FastLock mode. For ω’ = 2ω, the
phase margin during FastLock will also remain constant. The charge pump current is programmed via MICROWIRE interface.
When the charge pump circuit receives an input to deliver 4 times the normal current per unit phase error, an open drain NMOS
on chip device (FoLD) switches in a second resistor element to ground. The user calculates the loop filter component values for
the normal steady state considerations. The device configuration ensures that as long as a second resistor equal to the primary
resistor value is wired in appropriately, the loop will lock faster without any additional stability considerations to account for.
1.9 POWER CONTROL
Each PLL is individually power controlled by device power-down (PWDN) bits. The Main_PWDN and Aux_PWDN bits determine
the state of power control. Activation of any PLL power-down condition results in the disabling of the respective N-counter and
de-biasing of its respective fIN input (to a high impedance state). The R-counter functionality also becomes disabled under this
condition.
The reference oscillator input block is powered down when both Main_PWDN and Aux_PWDN bits are asserted. The OSCin pin
reverts to a high impedance state when this condition exists. Power down forces the respective charge pump and phase comparator logic to a TRI-STATE condition. During the power down condition, both N- and R-counters are held at reset. Upon powering up, the N-counter resumes counting in “close” alignment with the R-counter. The maximum error is at most one prescaler
cycle. The MICROWIRE interface remains active and it is capable of loading and latching in data during all of the power down
modes.
2.0 Programming Description
2.1 MICROWIRE INTERFACE
The LMX237x register set can be accessed through the MICROWIRE interface. A 22-bit shift register is used as a temporary register to indirectly program the on-chip registers. The shift register consists of a 20-bit DATA[19:0] field and a 2-bit ADDRESS[1:0]
field as shown below. The address field is used to decode the internal register address. Data is clocked into the shift register in
the direction from MSB to LSB, when the CLOCK signal goes high. On the rising edge of Load Enable (LE) signal, data stored
in the shift register is loaded into the addressed latch.
MSB
LSB
DATA[19:0]
ADDRESS[1:0]
21
2
1
0
2.1.1 Registers’ Address Map
When Load Enable (LE) is transitioned high, data is transferred from the 22-bit shift register into the appropriate latch depending
on the state of the ADDRESS[1:0] bits. A multiplexing circuit decodes these address bits and writes the data field to the corresponding internal register.
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ADDRESS[1:0]
REGISTER
FIELD
ADDRESSED
0
0
Aux_R Register
0
1
Aux_N Register
1
0
Main_R Register
1
1
Main_N Register
12
13
P_
Aux
Aux_
N18
Aux_
N19
Aux_
R18
Aux_
PWDN
Aux_
R19
FoLD 1 FoLD 0
Aux_
N17
Aux_
R17
Aux_
CPo_
TRI
19
Aux_
N16
Aux_
R16
Aux_
CPo_
4X
18
Aux_
N15
Aux_
R15
Aux_
PD_
POL
17
Main_N
P_
Main
Main_
N18
Main_
N19
Main_
R18
Main_
PWDN
Main_
R19
Aux_
N14
Aux_
R14
16
Aux_
N13
Aux_
R13
15
Aux_
R11
13
Aux_
N12
Aux_
N11
11
Aux_
R10
Aux_
N10
Aux_
N9
Aux_
R9
Data Field
12
9
8
Aux_
N7
Aux_
R7
Aux_
N6
Aux_
R6
Main_R_CNTR[14:0]
Aux_
N8
Aux_
R8
Aux_R_CNTR[14:0]
10
SHIFT REGISTER BIT LOCATION
Aux_B_CNTR[12:0]
Aux_
R12
14
Aux_
N5
Aux_
R5
7
Aux_
N4
Aux_
R4
6
Aux_
R2
4
Aux_
R1
3
Aux_
N3
Aux_
N2
Aux_
N1
Aux_A_CNTR[4:0]
Aux_
R3
5
Aux_
N0
Aux_
R0
Main_A_CNTR[4:0]
Main_ Main_ Main_ Main_ Main_ Main_ Main_ Main_ Main_ Main_ Main_ Main_ Main_ Main_ Main_ Main_ Main_ Main_
N17
N16
N15
N14
N13
N12
N11
N10
N9
N8
N7
N6
N5
N4
N3
N2
N1
N0
Main_B_CNTR[12:0]
0
1
1
0
0
1
0
1
0
Address Field
1
Least Significant Bit
2
Main_ Main_ Main_ Main_ Main_ Main_ Main_ Main_ Main_ Main_ Main_ Main_ Main_ Main_ Main_ Main_ Main_ Main_
R17
R16
R15
R14
R13
R12
R11
R10
R9
R8
R7
R6
R5
R4
R3
R2
R1
R0
Main_R FoLD 3 FoLD 2 Main_ Main_ Main_
CPo_ CPo_
PD_
TRI
4X
POL
Aux_N
Aux_R
20
(Continued)
LMX2370/LMX2371/LMX2372
21
Most Significant Bit
2.1.2 Registers’ Truth Table
2.0 Programming Description
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(Continued)
2.2 PROGRAMMABLE REFERENCE DIVIDERS (Main and Aux R Counters)
2.2.1 Aux_R Register
If the ADDRESS[1:0] field is set to 0 0, data is transferred from the 22-bit shift register into the Aux_R register when Load Enable
(LE) signal goes high. The Aux_R register sets the Aux PLL’s 15-bit R-counter divide ratio and various programmable modes. The
divide ratio is put into the Aux_R_CNTR[14:0] field. The divider ratio must be ≥ 2. For the description of bits Aux_R15–Aux_R19
see Section 2.4.
Most Significant Bit
21
20
19
18
SHIFT REGISTER BIT LOCATION
17
16
15
14
13
12
11
10
9
8
7
Least Significant Bit
6
5
4
3
2
1
0
Address Field
Aux_R_CNTR[14:0]
0
Aux_R0
Aux_R1
Aux_R2
Aux_R3
Aux_R4
Aux_R5
Aux_R6
Aux_R7
Aux_R8
Aux_R9
Aux_R10
Aux_R11
Aux_R12
Aux_R13
0
Aux_R14
Aux_R15 Aux_PD_POL
Aux_CPo_4X
Aux_R16
FoLD 0
Aux_R18
Aux_R19
FoLD 1
Aux_R
Aux_R17 Aux_CPo_TRI
Data Field
2.2.2 Main_R Register
If the ADDRESS[1:0] field is set to 1 0, data is transferred from the 22-bit shift register into the Main_R register which sets the
Main PLL’s 15-bit R-counter divide ratio when Load Enable (LE) signal goes high. The divide ratio is put into the
Main_R_CNTR[14:0] field. The divider ratio must be ≥ 2. For the description of bits Main_R15–Main_R19 see Section 2.4.
Most Significant Bit
21
20
19
18
SHIFT REGISTER BIT LOCATION
17
16
15
14
13
12
11
10
9
8
7
Least Significant Bit
6
5
4
3
2
1
0
Address Field
Main_R_CNTR[14:0]
0
Main_R0
Main_R1
Main_R2
Main_R3
Main_R4
Main_R5
Main_R6
Main_R7
Main_R8
Main_R9
Main_R10
Main_R11
Main_R12
Main_R13
1
Main_R14
Main_R15 Main_PD_POL
Main_CPo_4X
Main_R16
FoLD 2
Main_R18
FoLD 3
Main_R17 Main_CPo_TRI
Data Field
Main_R
Main_R19
LMX2370/LMX2371/LMX2372
2.0 Programming Description
2.2.3 Reference Divide Ratio (Main and Auxiliary R-Counters)
If the ADDRESS[1:0] field is set to 0 0 or 1 0 (00 for Aux and 10 for Main) data is transferred MSB first from the 22-bit shift register
into a latch which sets the respective 15-bit R-counter. Serial data format is shown below.
Main_R_CNTR[14:0] or Aux_R_CNTR[14:0]
Divide Ratio
R14
R13
R12
R11
R10
R9
R8
R7
R6
R5
R4
R3
R2
R1
R0
2
0
0
0
0
0
0
0
0
0
0
0
0
0
1
0
3
0
0
0
0
0
0
0
0
0
0
0
0
0
1
1
•
32,767
•
1
•
1
•
1
•
1
•
1
•
1
•
1
•
1
•
1
•
1
•
1
•
1
•
1
•
1
1
•
Note: R-counter divide ratio must be from 2 to 32,767.
2.3 PROGRAMMABLE FEEDBACK [N] DIVIDERS
2.3.1 Aux_N Register
If the ADDRESS[1:0] field is set to 0 1, data is transferred from the 22-bit shift register into the Aux_N register which sets the Auxiliary PLL’s 18-bit N-counter, prescaler value and power-down bit. The 18-bit N-counter consists of a 5-bit swallow
counter, Aux_A_CNTR[4:0], and a 13-bit programmable counter, Aux_B_CNTR[12:0]. Serial data format is shown below.
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14
Most Significant Bit
21
20
19
18
(Continued)
SHIFT REGISTER BIT LOCATION
17
16
15
14
13
12
11
10
9
8
Least Significant Bit
7
6
5
4
3
2
1
Address Field
Aux_B_CNTR[12:0]
Aux_A_CNTR[4:0]
1
Aux_N0
Aux_N1
Aux_N2
Aux_N3
Aux_N4
Aux_N5
Aux_N6
Aux_N7
Aux_N8
Aux_N9
Aux_N10
Aux_N11
Aux_N12
Aux_N13
Aux_N14
Aux_N15
Aux_N16
Aux_N17
0
Aux_N18
Aux_N19 Aux_PWDN
P_Aux
Data Field
Aux_N
0
2.3.2 Main_N Register
If the ADDRESS[1:0] field is set to 1 1, data is transferred from the 22-bit shift register into the Main_N register which sets the
Main PLL’s 18-bit N-counter, prescaler value and power-down bit. The 18-bit N-counter consists of a 5-bit swallow counter,
Main_A_CNTR[4:0], and a 13-bit programmable counter, Main_B_CNTR[12:0]. Serial data format is shown below.
Most Significant Bit
21
20
19
18
SHIFT REGISTER BIT LOCATION
17
16
15
14
13
12
11
10
9
8
7
Least Significant Bit
6
5
4
3
2
1
P_Main
Main_B_CNTR[12:0]
Main_A_CNTR[4:0]
1
Main_N0
Main_N1
Main_N2
Main_N3
Main_N4
Main_N5
Main_N6
Main_N7
Main_N8
Main_N9
Main_N10
Main_N11
Main_N12
Main_N13
Main_N14
Main_N15
Main_N16
Main_N17
1
Main_N18
Main_N19 Main_PWDN
Main_N
0
Address Field
Data Field
2.3.3 Feedback Divide Ratio (Main B Counter, Auxiliary B Counter)
Main_B_CNTR[12:0] or Aux_B_CNTR[12:0]
Divide Ratio
N17
N16
N15
N14
N13
N12
N11
N10
N9
N8
N7
N6
N5
3
0
0
0
0
0
0
0
0
0
0
0
1
1
4
0
0
0
0
0
0
0
0
0
0
1
0
1
•
8,191
•
1
•
1
•
1
•
1
•
1
•
1
•
1
•
1
•
1
•
1
•
1
•
1
•
1
Note: B-counter divide ratio must be ≥ 3.
2.3.4 Swallow Counter Divide Ratio (Main A Counter, Auxiliary A Counter)
Main_A_CNTR[4:0] or Aux_A_CNTR[4:0]
Divide Ratio
Main_N4
Main_N3
Main_N2
Main_N1
Main_N0
0
0
0
0
0
0
1
0
0
0
0
1
Notes: A
•
•
•
•
•
•
31
1
1
1
1
1
< P,
B
> A.
15
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LMX2370/LMX2371/LMX2372
2.0 Programming Description
LMX2370/LMX2371/LMX2372
2.0 Programming Description
(Continued)
2.3.5 PLL Prescaler Select (P_Aux, P_Main)
The LMX2370, LMX2371 and LMX2372 contain two dual modulus prescalers. A 32/33 or a 16/17 prescaler can be selected for
the 2.5 GHz and 2.0 GHz RF synthesizers in the LMX2370 and LMX2371 respectively. The 16/17 prescaler is only rated for input
frequencies below 1.2 GHz. A 16/17 or an 8/9 prescaler can be selected for the both 1.2 GHz synthesizers on the LMX2372 as
well as the 1.2 GHz synthesizers on the LMX2370 and LMX2371. The 8/9 prescaler is only rated for input frequencies below
550 MHz.
Prescaler Value
P_Main, (Main_N18) or
P_Aux (Aux_N18)
2.5 GHz PLL
2.0 GHz PLL
0
16/17
16/17
8/9
1
32/33
32/33
16/17
1.2 GHz PLL
Allowable Prescaler Values
PLL Input Frequency
2.5 GHz PLL
2.0 GHz PLL
fIN > 1.2 GHz
32/33
32/33
1.2 GHz PLL
NA
550 < fIN < 1200 MHz
16/17 or 32/33
16/17 or 32/33
16/17
fIN < 550 MHz
16/17 or 32/33
16/17 or 32/33
8/9 or 16/17
2.3.5.1 Pulse Swallow Function
fVCO = [(P x B) + A] x fOSC/R
fVCO:
B:
A:
fOSC:
R:
P:
Output frequency of external voltage controlled oscillator (VCO)
Preset divide ratio of binary 13-bit programmable counter (3 to 8191)
Preset divide ratio of binary 5-bit swallow counter
0 ≤ A ≤ 31 {P=32}
0 ≤ A ≤ 15 {P=16}
0 ≤ A ≤ 7 {P=8}
A≤B
Output frequency of the external reference frequency oscillator
Preset divide ratio of binary 15-bit programmable reference counter (3 to 32767)
Preset modulus of dual modulus prescaler (P = 8, 16, or 32)
2.3.6 PLL Power Down Control (Aux_PWDN, Main_PWDN)
The Aux_PWDN (Aux_N19) and Main_PWDN (Main_N19) bits are used to power down either the Main or Auxiliary PLL’s charge
pump portion, or the entire PLL block depending on the setting of the respective charge pump TRI-STATE bit (Aux_CPo_TRI or
Main_CPo_TRI) in the R_CNTR register. The power-down mechanism is described below. The R and N counters for each respective PLL are disabled and held at reset during the synchronous and asynchronous power down modes. This will allow a smooth
acquisition of the Main RF signal when the oscillator input buffer is still active (Auxiliary loop powered up) and vice versa. Upon
powering up, both R and N counters will start at the “zero” state, and the relationship between R and N will not be random.
Synchronous Power Down Mode
One of the PLL loops can be synchronously powered down by first setting the respective loop’s TRI-STATE mode bit LOW (R17
= 0) and then asserting its power down mode bit (N19 = 1). The power down function is gated by the charge pump. Once the
power down program bits Aux_PWDN (Aux_N19) and Main_PWDN (Main_N19) and TRI-STATE bits Aux_CPo_TRI (Aux_R17)
or Main_CPo_TRI (Main_R17) are loaded, the part will go into power down mode upon the completion of a charge pump pulse
event.
Asynchronous Power Down Mode
One of the PLL loops can be asynchronously powered down by first setting the respective loop’s TRI-STATE mode bit HI (R17
= 1) and then asserting its power down mode bit (N19 = 1). The power down function is NOT gated by the charge pump. Once
the power down program bits Aux_PWDN (Aux_N19) and Main_PWDN (Main_N19) and its respective TRI-STATE bit Aux_CPo_TRI (Aux_R17) or Main_CPo_TRI (Main_R17) are loaded, the part will go into power down mode immediately.
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16
(Continued)
2.3.7 Power Down Mode Table
Auxiliary PLL
Main
Counters
Active
Active
Active
Powered Down
Powered Down
Active
OFF
ON
ON
Powered Down
Powered Down
OFF
OFF
OFF
Main PLL
Auxiliary
Counters
OSCin Buffer
ON
ON
ON
ON
OFF
ON
2.4 PROGRAMMABLE MODES
Several modes of operation can be programmed with bits R15–R19 including the phase detector polarity, charge pump magnitude, charge pump TRI-STATE and the output of the Fo/LD pin. The programmable modes are shown in Table 1. Truth table for
the programmable modes and Fo/LD output are shown in Table 2 and Table 3.
2.4.1 Programmable Modes Table
R19
R18
fOUT/Lock Detect
R17
R16
R15
Charge
Pump
TRI-STATE
Charge
Pump
Magnitude
Phase
Detector
Polarity
Address[1:0]
FoLD 1
FoLD 0
Aux_CPo_TRI
Aux_CPo_4X
Aux_PD_POL
00
FoLD 3
FoLD 2
Main_CPo_TRI
Main_CPo_4X
Main_PD_POL
10
2.4.2 Mode Select Truth Table
CPo_TRI (Note 7)
CPo_4X (Note 8)
0
Normal Operation
1X Current
PD_POL (Note 9)
LOW
1
TRI-STATE
4X Current
HIGH
Note 7: Both synchronous and asynchronous power down modes are available with the LMX237x family to be able to adapt to different types of applications. The
MICROWIRE control register remains active and capable of loading and latching in data during all of the powerdown modes.
Note 8: ICPo (charge pump current magnitude) is dependent on Vp. The ICPo LOW current state = 1/4 x ICPo HIGH current.
Note 9: See Section 2.4.3
2.4.3 Phase Detector Polarity (Aux_PD_POL, Main_PD_POL)
Depending upon VCO characteristics, the Aux_PD_POL
(Aux_R15) and Main_PD_POL (Main_R15) bits should be
set accordingly:
When VCO characteristics are positive like (1), R15 should
be set HIGH;
When VCO characteristics are negative like (2), R15 should
be set LOW.
VCO CHARACTERISTICS
DS101026-5
17
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LMX2370/LMX2371/LMX2372
2.0 Programming Description
LMX2370/LMX2371/LMX2372
2.0 Programming Description
(Continued)
2.4.4 The FoLD Output Truth Table
Main
R[18]
Aux
R[18]
Main
R[19]
Aux
R[19]
0
0
0
0
Disabled
0
1
0
0
Aux Lock Detect (Note 10)
1
0
0
0
Main Lock Detect (Note 10)
1
1
0
0
Main/Aux Lock Detect (Note 10)
X
0
0
1
Aux Reference Divider Output
X
0
1
0
Main Reference Divider Output
X
1
0
1
Aux Programmable Divider Output
X
1
1
0
Main Programmable Divider Output
0
0
1
1
FastLock Output. Open Drain Output (Note 11)
0
1
1
1
Reset Aux R and N Counters and TRI-STATE Aux Charge Pump (Note 12)
1
0
1
1
Reset Main R and N Counters and TRI-STATE Main Charge Pump (Note
12)
1
1
1
1
Reset All Four Counters and TRI-STATE both Charge Pumps (Note 12)
Fo/LD Output State
X - don’t care condition
Note 10: Open drain lock detect output is provided to indicate when the VCO frequency is in “lock”. When the loop is locked and a lock detect mode is selected,
the pin is HIGH, with narrow pulses LOW. In the Main/Aux lock detect mode a locked condition is indicated when Main and Aux are both locked.
Note 11: The FastLock mode utilizes the FoLD output pin to switch a second loop filter damping resistor to ground during FastLock operation. Activation of FastLock
occurs whenever the Main loop’s ICPo magnitude bit R[16] is selected HI while the R[18] and R[19] mode bits are set.
Note 12: Aux and Main PLLs can be reset independently from each other by using the R[18] and R[19] bits. The Aux Counter Reset mode resets Aux PLL’s R and
N counters and brings Aux charge pump output to TRI-STATE condition. The Main Counter Reset mode resets Main PLL’s R and N counters and brings Main charge
pump output to a TRI-STATE condition. The Aux and Main Counter Reset modes reset all counters and bring both charge pump outputs to a TRI-STATE condition.
Upon removal of the Reset bits, the N counter resumes counting in “close” alignment with the R counter. (The maximum error is one prescaler cycle.)
2.5 Serial Data Input Timing
Serial Data Input Timing
DS101026-6
NOTES: Parenthesis data indicates programmable reference divider data.
Data shifted into register on clock rising edge.
Data is shifted in MSB first.
TEST CONDITIONS: The Serial Data Input Timing is tested using a symmetrical waveform around VCC/2. The test waveform has an edge rate of 0.6 V/ns with
amplitudes of 2.2V @ VCC = 2.7V and 2.6V @ VCC = 5.5V.
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18
LMX2370/LMX2371/LMX2372
2.0 Programming Description
(Continued)
2.6 Typical Lock Detect Timing
Typical Lock Detect Timing
DS101026-7
19
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LMX2370/LMX2371/LMX2372
Typical Application Example
DS101026-36
Operational Notes:
*
VCO is assumed AC coupled.
**
RIN increases impedance so that VCO output power is provided to the load rather than the PLL. Typical values are 10Ω to
200Ω depending on the VCO power level. fIN RF impedance ranges from 40Ω to 100Ω. fIN IF impedances are higher.
***
50Ω termination is often used on test boards to allow use of external reference oscillator. For most typical products a
CMOS clock is used and no terminating resistor is required. OSCin may be AC or DC coupled. AC coupling is recommended because the input circuit provides its own bias. (See Figure below)
**** Adding RC filters to the VCC line is recommended to reduce loop-to-loop noise coupling.
DS101026-37
Proper use of grounds and bypass capacitors is essential to achieve a high level of performance. Crosstalk between pins can be reduced by careful board
layout.
This is an electrostatic sensitive device. It should be handled only at static free work stations.
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20
LMX2370/LMX2371/LMX2372
Application Information
A block diagram of the basic phase locked loop is shown in Figure 1.
DS101026-38
FIGURE 1. Basic Charge Pump Phase Locked Loop
LOOP GAIN EQUATIONS
A linear control system model of the phase feedback for a
PLL in the locked state is shown in Figure 2. The open loop
gain is the product of the phase comparator gain (Kφ), the
VCO gain (KVCO/s), and the loop filter gain Z(s) divided by
the gain of the feedback counter modulus (N). The passive
loop filter configuration used is displayed in Figure 3, while
the complex impedance of the filter is given in Equation (2).
(5)
From Equation (3) we can see that the phase term will be dependent on the single pole and zero such that the phase
margin is determined in Equation (6).
φ(ω) = tan−1 (ω • T2) − tan−1 (ω • T1) + 180˚
(6)
A plot of the magnitude and phase of G(s)H(s) for a stable
loop, is shown in Figure 4 with a solid trace. The parameter
φp shows the amount of phase margin that exists at the point
the gain drops below zero (the cutoff frequency wp of the
loop). In a critically damped system, the amount of phase
margin would be approximately 45 degrees.
If we were now to redefine the cut off frequency, wp’, as
double the frequency which gave us our original loop bandwidth, wp, the loop response time would be approximately
halved. Because the filter attenuation at the comparison frequency also diminishes, the spurs would have increased by
approximately 6 dB. In the proposed Fastlock scheme, the
higher spur levels and wider loop filter conditions would exist
only during the initial lock-on phase — just long enough to
reap the benefits of locking faster. The objective would be to
open up the loop bandwidth but not introduce any additional
complications or compromises related to our original design
criteria. We would ideally like to momentarily shift the curve
of Figure 4 over to a different cutoff frequency, illustrated by
the dotted line, without affecting the relative open loop gain
and phase relationships. To maintain the same gain/phase
relationship at twice the original cutoff frequency, other terms
in the gain and phase Equations (5), (6) will have to compensate by the corresponding “1/w” or “1/w2” factor. Examination
of Equations (3), (4), (6) indicates the damping resistor variable R2 could be chosen to compensate the “w” terms for the
phase margin. This implies that another resistor of equal
value to R2 will need to be switched in parallel with R2 during
the initial lock period. We must also ensure that the magnitude of the open loop gain, H(s)G(s) is equal to zero at wp’ =
2wp. KVCO, Kφ, N, or the net product of these terms can be
changed by a factor of 4, to counteract the w2 term present
in the denominator of Equations (3), (4). The Kφ term was
chosen to complete the transformation because it can
readily be switch between 1X and 4X values. This is accomplished by increasing the charge pump output current from 1
mA in the standard mode to 4 mA in Fastlock.
DS101026-39
FIGURE 2. PLL Linear Model
DS101026-40
FIGURE 3. Passive Loop Filter
(1)
(2)
The time constants which determine the pole and zero frequencies of the filter transfer function can be defined as
(3)
and
T2 = R2 • C2
(4)
The 3rd order PLL Open Loop Gain can be calculated in
terms of frequency, ω, the filter time constants T1 and T2,
and the design constants Kφ, KVCO, and N.
21
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LMX2370/LMX2371/LMX2372
Application Information
(Continued)
DS101026-43
FIGURE 4. Open Loop Response Bode Plot
FASTLOCK CIRCUIT IMPLEMENTATION
A diagram of the Fastlock scheme as implemented in National Semiconductors LMX233xA PLL is shown in Figure 5.
When a new frequency is loaded, and the RF Icpo bit is set
high the charge pump circuit receives an input to deliver 4
times the normal current per unit phase error while an open
drain NMOS on chip device switches in a second R2 resistor
element to ground. The user calculates the loop filter component values for the normal steady state considerations. The
device configuration ensures that as long as a second iden-
tical damping resistor is wired in appropriately, the loop will
lock faster without any additional stability considerations to
account for. Once locked on the correct frequency, the user
can return the PLL to standard low noise operation by sending a MICROWIRE instruction with the RF Icpo bit set low.
This transition does not affect the charge on the loop filter
capacitors and is enacted synchronous with the charge
pump output. This creates a nearly seamless change between Fastlock and standard mode.
DS101026-44
FIGURE 5. Fastlock PLL Architecture
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22
LMX2370/LMX2371/LMX2372
Physical Dimensions
inches (millimeters) unless otherwise noted
Thin Shrink Small Outline (TSSOP) Package
Order Number LMX2370TM, LMX2371TM or LMX2372TM
*For Tape and Reel (2500 units per reel)
Order Number LMX2370TMX, LMX2371TMX or LMX2372TMX
NS Package Number MTC20
23
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LMX2370/LMX2371/LMX2372 PLLatinum Dual Frequency Synthesizer for RF Personal
Communications
Physical Dimensions
inches (millimeters) unless otherwise noted (Continued)
Chip Scale Package
For Tape and Reel (2500 Units Per Reel)
Order Numbers: LMX2370SLBX, LMX2371SLBX, LMX2372SLBX
NS Package Number SLB24A
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can be reasonably expected to cause the failure of
the life support device or system, or to affect its
safety or effectiveness.
National Semiconductor
Asia Pacific Customer
Response Group
Tel: 65-2544466
Fax: 65-2504466
Email: [email protected]
National Semiconductor
Japan Ltd.
Tel: 81-3-5639-7560
Fax: 81-3-5639-7507
National does not assume any responsibility for use of any circuitry described, no circuit patent licenses are implied and National reserves the right at any time without notice to change said circuitry and specifications.