The LMX2301 is a high performance frequency synthesizer
designed for RF operation up to 160 MHz. It is fabricated
using National’s ABiC IV BiCMOS process.
LMX2301, which employs the digital phase lock loop technique, combined with a high quality reference oscillator and
a loop filter, provides the tuning voltage for the voltage controlled oscillator to generate a very stable, low noise local
oscillator signal.
Serial data is transferred into the LMX2301 via a three line
MICROWIRE
age can range from 2.7V to 5.5V.
The LMX2301 features very low current consumption, typically 2 mA at 3V.
The LMX2301 is available in a TSSOP 20-pin surface mount
plastic package.
TM
interface (Data, Enable, Clock). Supply volt-
Block Diagram
Features
Y
RF operation up to 160 MHz
Y
2.7V to 5.5V operation
Y
Low current consumption:
e
I
2 mA (typ) at V
CC
Y
Internal balanced, low leakage charge pump
Y
Small-outline, plastic, surface mount TSSOP,
0.173
wide package
×
CC
e
3V
Applications
Y
Analog Cellular telephone systems
(AMPS, ETACS, NMT)
TRI-STATEÉis a registered trademark of National Semiconductor Corporation.
TM
MICROWIRE
C
1996 National Semiconductor CorporationRRD-B30M126/Printed in U. S. A.
and PLLatinumTMare trademarks of National Semiconductor Corporation.
TL/W/12458
TL/W/12458– 1
http://www.national.com
Connection Diagram
LMX2301
20-Lead (0.173×Wide) Thin Shrink
TL/W/12458– 2
Small Outline Package (TM)
Order Number LMX2301TM or LMX2301TMX
See NS Package Number MTC20
Pin Descriptions
Pin No.Pin NameI/ODescription
1OSC
3OSC
4V
5V
6D
IN
OUT
P
CC
o
7GNDGround.
8LDOLock detect. Output provided to indicate when the VCO frequency is in ‘‘lock’’. When the loop is
10f
IN
11CLOCKIHigh impedance CMOS Clock input. Data is clocked in on the rising edge, into the various
13DATAIBinary serial data input. Data entered MSB first. LSB is control bit. High impedance CMOS input.
14LEILoad enable input (with internal pull-up resistor). When LE transitions HIGH, data stored in the
15FCIPhase control select (with internal pull-up resistor). When FC is LOW, the polarity of the phase
16BISWOAnalog switch output. When LE is HIGH, the analog switch is ON, routing the internal charge
17f
18w
OUT
p
19PWDNIPower Down (with internal pull-up resistor).
20w
r
2,9,12NCNo connect.
IOscillator input. A CMOS inverting gate input intended for connection to a crystal resonator for
operation as an oscillator. The input has a V
external CMOS or TTL logic gate. May also be from a reference oscillator.
/2 input threshold and can be driven from an
CC
OOscillator output.
Power supply for charge pump. Must betVCC.
Power supply voltage input. Input may range from 2.7V to 5.5V. Bypass capacitors should be
placed as close as possible to this pin and be connected directly to the ground plane.
OInternal charge pump output. For connection to a loop filter for driving the input of an external
VCO.
locked, the pin’s output is HIGH with narrow low pulses.
IRF buffer input. Small signal input from the VCO.
counters and registers.
shift registers is loaded into the appropriate latch (control bit dependent). Clock must be low
when LE toggles high or low. See Serial Data Input Timing Diagram.
comparator and charge pump combination is reversed.
pump output through BISW (as well as through D
).
o
OMonitor pin of phase comparator input. CMOS output.
OOutput for external charge pump. wpis an open drain N-channel transistor and requires a pull-up
resistor.
e
PWDN
PWDNeLOW for power saving.
Power down function is gated by the return of the charge pump to a TRI-STATE condition.
HIGH for normal operation.
OOutput for external charge pump. wris a CMOS logic output.
http://www.national.com2
Functional Block Diagram
Note 1: The power down function is gated by the charge pump to prevent any unwanted frequency jumps. Once the power down pin is brought low the part will go
into power down mode when the charge pump reaches a TRI-STATE condition.
TL/W/12458– 3
http://www.national.com3
Absolute Maximum Ratings (Notes 1 and 2)
If Military/Aerospace specified devices are required,
please contact the National Semiconductor Sales
Office/Distributors for availability and specifications.
Power Supply Voltage
V
CC
V
P
Voltage on Any Pin
with GND
e
0V (VI)
Storage Temperature Range (TS)
Lead Temperature (TL) (solder, 4 sec.)
b
0.3V toa6.5V
b
0.3V toa6.5V
b
0.3V to V
b
65§Ctoa150§C
CC
a
a
0.3V
260§C
Recommended Operating
Conditions
Power Supply Voltage
V
CC
V
P
Operating Temperature (TA)
Note 1: 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 2: This device is a high performance RF integrated circuit with an ESD
k
2 keV and is ESD sensitive. Handling and assembly of this device
rating
should only be done at ESD workstations.
2.7V to 5.5V
VCCtoa5.5V
b
40§Ctoa85§C
Electrical Characteristics V
CC
e
5V, V
e
5V;b40§CkT
P
k
85§C, except as specified
A
SymbolParameterConditionsMinTypMaxUnits
I
CC
I
CC-PWDN
f
IN
f
OSC
f
w
Pf
IN
V
OSC
V
IH
V
IL
I
IH
I
IL
I
IH
I
IL
I
IH
I
IL
*Except fINand OSC
Power Supply CurrentV
Power Down CurrentV
RF Input Operating Frequency45160MHz
Oscillator Input Operating Frequency520MHz
Phase Detector Frequency10MHz
Input SensitivityV
Oscillator SensitivityOSC
High-Level Input Voltage*0.7 V
Low-Level Input Voltage*0.3 V
High-Level Input Current (Clock, Data)V
Low-Level Input Current (Clock, Data)V
Oscillator Input CurrentV
High-Level Input Current (LE, FC)V
Low-Level Input Current (LE, FC)V
IN
e
3.0V2.05mA
CC
e
V
5.0V3.0mA
CC
e
3.0V30180mA
CC
e
V
5.0V60350mA
CC
CC
IH
IL
IH
V
IL
IH
IL
e
2.7V to 5.5V
IN
e
V
CC
e
0V, V
e
V
CC
e
0V, V
e
V
CC
e
0V, V
e
5.5V
e
5.5V
CC
e
5.5V100mA
e
5.5V
CC
e
5.5V
e
5.5V
CC
b
10
0.5V
CC
b
1.01.0mA
b
1.01.0mA
b
100mA
b
1.01.0mA
b
1001.0mA
a
6dBm
CC
PP
V
V
http://www.national.com4
Electrical Characteristics V
CC
e
5.0V, V
e
5.0V;b40§CkT
P
k
85§C, except as specified (Continued)
A
SymbolParameterConditionsMinTypMaxUnits
I
Do-source
I
Do-sink
I
Do-Tri
V
OH
V
OL
V
OH
V
OL
I
OL
I
OH
R
ON
t
CS
t
CH
t
CWH
t
CWL
t
ES
t
EW
**Except OSC
Charge Pump Output CurrentV
Charge Pump TRI-STATEÉCurrent0.5VsV
High-Level Output VoltageI
Low-Level Output VoltageI
High-Level Output Voltage (OSC
Low-Level Output Voltage (OSC
)I
OUT
)I
OUT
Open Drain Output Current (wp)V
Open Drain Output Current (wp)V
e
VP/2
D
o
e
V
VP/25.0mA
D
o
s
b
V
D
o
e
T
25§C
A
eb
1.0 mA**V
OH
e
1.0 mA**0.4V
OL
eb
200 mAV
OH
e
200 mA0.4V
OL
e
5.0V, V
CC
e
5.5V100mA
OH
0.5V
P
e
0.4V1.0mA
OL
b
5.05.0nA
b
CC
b
CC
Analog Switch ON Resistance100X
Data to Clock Set Up TimeSee Data Input Timing50ns
Data to Clock Hold TimeSee Data Input Timing10ns
Clock Pulse Width HighSee Data Input Timing50ns
Clock Pulse Width LowSee Data Input Timing50ns
Clock to Enable Set Up TimeSee Data Input Timing50ns
Enable Pulse WidthSee Data Input Timing50ns
OUT
b
5.0mA
0.8V
0.8V
http://www.national.com5
Functional Description
The simplified block diagram below shows the 19-bit data register, the 14-bit R Counter and the R15 Latch, and the 11-bit
N Counter (intermediate latches are not shown). The data stream is clocked (on the rising edge) into the DATA input, MSB first.
If the Control Bit (last bit input) is HIGH, the DATA is transferred into the R Counter (programmable reference divider) and the
S Latch (power up counter reset). If the Control Bit (LSB) is LOW, the DATA is transferred into the N Counter (programmable
divider).
TL/W/12458– 1
PROGRAMMABLE REFERENCE DIVIDER (R COUNTER) AND COUNTER RESET (R15 LATCH)
If the Control Bit (last bit shifted into the Data Register) is HIGH, data is transferred from the 19-bit shift register into a 14-bit
latch (which sets the 14-bit R Counter) and the 1-bit R15 Latch, which can be used to force an immediate load of the R and N
counters during a cold power up condition. Serial data format is shown below.
14-BIT PROGRAMMABLE REFERENCE DIVIDER RATIO
(R COUNTER)
Divide
Ratio
14R13R12R11R10
R
RR9R8R7R6R5R4R3R2R
1
3 0 0 0 0 0 000000011
4 0 0 0 0 0 000000100
# # # # # # #########
16383 1 1 1 1 1 1 1 1 1 1 1 1 1 1
Notes: Divide ratios less than 3 are prohibited.
Divide ratio: 3 to 16383
R1 to R14: These bits select the divide ratio of the programmable
reference divider.
C: Control bit (set to HIGH level to load R counter and R15 Latch)
Data is shifted in MSB first.
SUGGESTED PROGRAMMING SEQUENCE AFTER COLD POWER-UP
1. Program N counter with desired divide ratio.
2. Program R counter with R15
3. Program R counter with R15e0 and desired divide ratio. (N and R counters start counting.)
http://www.national.com6
e
1 and desired divide ratio. (N and R counters hold at load state.)
TL/W/12458– 14
1-BIT COUNTER RESET
(R15 LATCH)
CounterR
Reset15
Remove
Forced Load
Force
Load State
0
1
The 1-bit counter reset latch controls
whether the R and N counters are immediately forced to load conditions
upon power up. If R[15
e
]
HIGH, the
N and R latch states are immediately
read into the respective counters.
Functional Description (Continued)
PROGRAMMABLE DIVIDER (N COUNTER)
The N counter consists of the 11-bit programmable counter. If the Control Bit (last bit shifted into the Data Register) is LOW,
data is transferred from the 19-bit shift register into an 11-bit latch, which sets the 11-bit programmable Counter. Serial data
format is shown below.
Note: R8 to R18: Programmable counter divide ratio control bits (3 to 2047)
7 LSB BITS OF N REGISTER
Divide N N N N N N N
Ratio7 6 5 4 3 2 1
X XXXXXXX
Note: XeDon’t care state
11-BIT PROGRAMMABLE COUNTER DIVIDE RATIO
Divide
Ratio
18N17N16N15N14N13N12N11N10
N
NN9N
8
3 00000000011
4 00000000100
# ###########
2047111111111 1 1
Note: Divide ratio: 3 to 2047 (Divide ratios less than 3 are prohibited)
TL/W/12458– 15
EQUATION FOR OUTPUT FREQUENCY
DETERMINATION
e
c
[N]
f
VCO
f
: Output frequency of external voltage controlled oscil-
VCO
f
lator (VCO)
OSC
/R
N:Preset divide ratio of binary 11-bit programmable
counter (3 to 2047)
f
: Output frequency of the external reference frequency
OSC
oscillator
R:Preset divide ratio of binary 14-bit programmable ref-
erence counter (3 to 16383)
http://www.national.com7
Functional Description (Continued)
SERIAL DATA INPUT TIMING
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 V
amplitudes of 2.2V
@
V
CC
e
2.7V and 2.6V@V
e
5.5V.
CC
Phase Characteristics
In normal operation, the FC pin is used to reverse the polarity of the phase detector. Both the internal and any external
charge pump are affected.
Depending upon VCO characteristics, FC pin should be set
accordingly:
When VCO characteristics are like (1), FC should be set
HIGH or OPEN CIRCUIT;
When VCO characteristics are like (2), FC should be set
LOW.
When FC is set HIGH or OPEN CIRCUIT, the monitor pin of
the phase comparator input, f
divider output, f
programmable divider output, f
. When FC is set LOW, f
r
PHASE COMPARATOR AND INTERNAL CHARGE PUMP CHARACTERISTICS
, is set to the reference
out
.
p
is set to the
out
TL/W/12458– 16
/2. The test waveform has an edge rate of 0.6 V/ns with
CC
VCO Characteristics
TL/W/12458– 17
Notes: Phase difference detection range:b2q toa2q
The minimum width pump up and pump down current pulses occur at the Dopin when the loop is locked.
e
FC
HIGH
http://www.national.com8
TL/W/12458– 18
Analog Switch
The analog switch is useful for radio systems that utilize a frequency scanning mode and a narrow band mode. The purpose of
the analog switch is to decrease the loop filter time constant, allowing the VCO to adjust to its new frequency in a shorter
amount of time. This is achieved by adding another filter stage in parallel. The output of the charge pump is normally through the
D
pin, but when LE is set HIGH, the charge pump output also becomes available at BISW. A typical circuit is shown below. The
o
second filter stage (LPF-2) is effective only when the switch is closed (in the scanning mode).
TL/W/12458– 19
Typical Crystal Oscillator Circuit
A typical circuit which can be used to implement a crystal
oscillator is shown below.
TL/W/12458– 20
Typical Lock Detect Circuit
A lock detect circuit is needed in order to provide a steady
LOW signal when the PLL is in the locked state. A typical
circuit is shown below.
TL/W/12458– 21
http://www.national.com9
Typical Application Example
Operational Notes:
* VCO is assumed AC coupled.
** R
increases impedance so that VCO output power is provided to the load rather than the PLL. Typical values are 10X to 200X depending on the VCO power
IN
level. f
RF impedance ranges from 40X to 100 X.
IN
*** 50X 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. OSC
Application Hints:
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.
may be AC or DC coupled. AC coupling is recommended because the input circuit provides its own bias. (See
IN
TL/W/12458– 23
TL/W/12458– 22
Figure
below)
http://www.national.com10
Application Information
LOOP FILTER DESIGN
A block diagram of the basic phase locked loop is shown.
FIGURE 1. Basic Charge Pump Phase Locked Loop
An example of a passive loop filter configuration, including
the transfer function of the loop filter, is shown in
Z(s)
e
s (C2#R2)a1
s2(C1#C2#R2)asC1asC2
Figure 2
TL/W/12458– 25
FIGURE 2. 2nd Order Passive Filter
Define the time constants which determine the pole and
zero frequencies of the filter transfer function by letting
T2eR2#C2(1a)
and
T1
#
C1aC2(1b)
C1#C2
e
R2
The PLL linear model control circuit is shown along with the
open loop transfer function in
detector and VCO gain constants[Kw and K
loop filter transfer function[Z(s)], the open loop Bode plot
Figure 3
. Using the phase
]
and the
VCO
can be calculated. The loop bandwidth is shown on the
Bode plot (
is shown to be the difference between the phase at the unity
gain point and
Open Loop Gaineii/i
Closed Loop Gaineio/i
0p) as the point of unity gain. The phase margin
b
180§.
e
H(s) G(s)
e
Kw Z(s) K
VCO
/Ns
e
e
G(s)/[1aH(s) G(s)
i
TL/W/12458– 27
]
.
FIGURE 3. Open Loop Transfer Function
Thus we can calculate the 3rd order PLL Open Loop Gain in
terms of frequency
G(s)
l
sej
e
0
#
2
0
H(s)
#
Kw#K
(1aj0#T2)
VCO
C1#N(1aj0#T1)
b
From equation 2 we can see that the phase term will be
dependent on the single pole and zero such that
b
1
e
w(
0)
tan
(0#T2)btan
b
1
(0#T1)a180§(3)
By setting
dw
d0
e
1a(0#T2)
T2
2
b
1a(0#T1)
T1
we find the frequency point corresponding to the phase inflection point in terms of the filter time constants T1 and T2.
This relationship is given in equation 5.
e
0
1/0T2#T1(5)
For the loop to be stable the unity gain point must occur
before the phase reaches
p
b
180 degrees. We therefore
want the phase margin to be at a maximum when the magnitude of the open loop gain equals 1. Equation 2 then gives
C1
e
Kw#K
0
p
2
VCO
#N#
#
T2
T1
(1aj0
(1aj0
Ó
T2)
#
p
T1)
#
p
TL/W/12458– 24
TL/W/12458– 26
T1
#
T2 (2)
e
0
2
Ó
(4)
(6)
http://www.national.com11
Application Information (Continued)
0
Ð0
c
p
p
(1
2
T2)
#
T1)
#
a
1
a
T12)(1
#
, and the
p
2
2
opt/fref
(T1aT3)
[
tanw
2
0
T22)
#
c
a
(7)
(9)
(10)
#
0
Therefore, if we specify the loop bandwidth,
phase margin, w
late the two time constants, T1 and T2, as shown in equations 7 and 8. A common rule of thumb is to begin your
design with a 45
From the time constants T1, and T2, and the loop bandwidth,
0
equations 9 to 11.
K
(MHz/V)Voltage Controlled Oscillator (VCO)
VCO
Kw (mA)Phase detector/charge pump gain
NMain divider ratio. Equal to RF
RF
(MHz)Radio Frequency output of the VCO at
opt
f
(kHz)Frequency of the phase detector in-
ref
T2
0
C1
, Equations 1 through 6 allow us to calcu-
p
phase margin.
§
e
T1
T2
, the values for C1, R2, and C2 are obtained in
p
T1
Kw#K
e
C1
#
T2
e
C2
Tuning Voltage constant. The frequency vs voltage tuning ratio.
constant. The ratio of the current output to the input phase differential.
which the loop filter is optimized.
puts. Usually equivalent to the RF
channel spacing.
e
e
c
e
1
2
0
(T1aT3)(15)
#
c
tanw#(T1aT3)
a
[
(T1
T3)
T1
Kw#K
#
T2
0
c
b
secw
tanw
p
p
0
p
1
e
2
0
T1(8)
#
p
1a(0
VCO
2
0
N
1a(0
#
0
p
T2
C1
R2
2
2
#
b
1
#
T1
#
J
T2
e
C2(11)
T1#T3
#
(1
Ð
#
]
a
0
a
VCO
N
In choosing the loop filter components a trade off must be
made between lock time, noise, stability, and reference
spurs. The greater the loop bandwidth the faster the lock
time will be, but a large loop bandwidth could result in higher
reference spurs. Wider loop bandwidths generally improve
close in phase noise but may increase integrated phase
noise depending on the reference input, VCO and division
ratios used. The reference spurs can be reduced by reducing the loop bandwidth or by adding more low pass filter
stages but the lock time will increase and stability will decrease as a result.
THIRD ORDER FILTER
A low pass filter section may be needed for some applications that require additional rejection of the reference sidebands, or spurs. This configuration is given in
order to compensate for the added low pass section, the
component values are recalculated using the new open
loop unity gain frequency. The degradation of phase margin
caused by the added low pass is then mitigated by slightly
increasing C1 and C2 while slightly decreasing R2.
The added attenuation from the low pass filter is:
Defining the additional time constant as
Then in terms of the attenuation of the reference spurs added by the low pass pole we have
We then use the calculated value for loop bandwidth
equation 11, to determine the loop filter component values
in equations 15 –17.
the frequency jump lock time will increase.
2
a
T1#T3
2
(T1aT3)
c
]
(/2
2
T32)
#
(
ATTEN
b
1
(
e
20 log[(2qf
T3eR3#C3(13)
e
T3
0
0
c
#R3#
ref
ATTEN/20
10
(2q#f
is slightly less than 0p, therefore
2
C3)
b
1
2
)
ref
Figure 4
a
1](12)
0
.In
(14)
c
(16)
(17)
in
http://www.national.com12
Application Information (Continued)
EXTERNAL CHARGE PUMP
The LMX PLLatinum series of frequency synthesizers are
equipped with an internal balanced charge pump as well as
outputs for driving an external charge pump. Although the
superior performance of NSC’s on board charge pump eliminates the need for an external charge pump in most applications, certain system requirements are more stringent. In
these cases, using an external charge pump allows the designer to take direct control of such parameters as charge
pump voltage swing, current magnitude, TRI-STATE leakage, and temperature compensation.
One possible architecture for an external charge pump current source is shown in
the diagram, correspond to the phase detector outputs of
the LMX2301 frequency synthesizer. These logic signals are
converted into current pulses, using the circuitry shown in
Figure 9
, to enable either charging or discharging of the
loop filter components to control the output frequency of the
PLL.
Referring to
Figure 9
current which is relatively constant to within 0.5V of the
power supply rail. To accomplish this, it is important to establish as large of a voltage drop across R5, R8 as possible
without saturating Q2, Q4. A voltage of approximately 300
mV provides a good compromise. This allows the current
source reference being generated to be relatively repeatable in the absence of good Q1, Q2/Q3, Q4 matching.
(Matched transistor pairs is recommended.) The wp and wr
outputs are rated for a maximum output load current of 1
mA while 5 mA current sources are desired. The voltages
developed across R4, 9 will consequently be approximately
258 mV, or 42 mV
À
ences
0.026*1n (5 mA/1 mA)Óthrough the Q1, Q2/Q3, Q4
pairs.
In order to calculate the value of R7 it is necessary to first
estimate the forward base to emitter voltage drop (Vfn,p) of
the transistors used, the V
of wr’s under 1 mA loads. (wp’s V
k
V
0.1V.)
OH
Knowing these parameters along with the desired current
allow us to design a simple external charge pump. Separating the pump up and pump down circuits facilitates the nodal analysis and give the following equations.
For Tape and Reel Order Number LMX2301TMX (2500 Units per Reel)
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DEVICES OR SYSTEMS WITHOUT THE EXPRESS WRITTEN APPROVAL OF THE PRESIDENT OF NATIONAL
SEMICONDUCTOR CORPORATION. As used herein:
1. Life support devices or systems are devices or2. A critical component is any component of a life
systems which, (a) are intended for surgical implantsupport device or system whose failure to perform can
into the body, or (b) support or sustain life, and whosebe reasonably expected to cause the failure of the life
failure to perform, when properly used in accordancesupport device or system, or to affect its safety or
with instructions for use provided in the labeling, caneffectiveness.
be reasonably expected to result in a significant injury
to the user.
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Americas
Tel: 1(800) 272-9959
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