Datasheet LMV248 Datasheet (National Semiconductor)

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LMV248
Dual Band GSM Power Controller

LMV248 Dual Band GSM Power Controller

September 2001

General Description

The LMV248 RF power amplifier controller allows simple
implementation of transmit power control loops in GSM and
DCS/PCS and mobile phones. The LMV248 supports, GaAs
HBT and bipolar RF power amplifiers. The device operates
from a single supply of 2.5V to 5V. The LMV248 includes an
error amplifier with an input summing network, input and
output band switches, input filters, and output drivers. Ana­log input signals processed are:

– Coupler/detector voltages from GSM and PCN band
power amplifier outputs.

– Base band DAC ramp signal.
– Temperature compensation diode voltages.
– Pre-bias voltage for faster PA control.
Selection of the GSM or PCN output driver is made using the

GSM/PCN band select pin.
The On/OFF pin allows rapid power up or shutdown of the

device during Tx or Rx slots. In the off mode, both output
drivers are set low for PA shutdown. In the on mode, the
non-active driver will remain low for continued PAshutdown.
A single external capacitor/resistor combination is used to
adjust the closed loop frequency response.

The LMV248 replaces multiple discrete parts, reducing
board area and cost. The LLP leadless package minimizes
board footprint and permits flexible optimized PCB place­ment.

Features

n Multi-band cellular operation (example: GSM, PCN)
n Support of GaAs HBT and bipolar technology
n Shutdown mode for power save in Rx slot (0.15µA)
n Integrated ramp filter
n Built-in current source for biasing Schottky diodes
n Pre-biasing of PA control gate voltage (V
n GPRS compliant
n External loop compensation
n Detector diode temperature compensation
n Miniature packaging: LLP-16: 4mm x 4mm x 0.8mm

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)

Applications

n GSM mobile phone
n TDMA RF control
n Wireless LAN
n PC and PDA modules
n GPS navigation modules

Connection Diagram

16-Pin LLP

Top View

Typical Application Circuit

10137201

10137202

FIGURE 1.

© 2001 National Semiconductor Corporation DS101372 www.national.com

Absolute Maximum Ratings (Note 1)

If Military/Aerospace specified devices are required,

LMV248

please contact the National Semiconductor Sales Office/
Distributors for availability and specifications.

Operating Temperature −40˚C
Storage Temperature Range −65˚C to 150˚C
Lead Temperature (solder, 4

sec) 260˚C

ESD Tolerance

Human Body Model (Note 1) 1500V
Machine Model 100V

Supply Voltage

V

to GND 5.5V

DD

Input Voltage Range

VfA, VfB, or TC to GND 10V
Ramp 0 to V
V

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0toV

DD
DD

Junction Temperature 150˚C max

Operating Ratings (Note 1)

Supply Voltage

V

to GND 2.5V to 5V

DD

Input Voltage

VfA, VfB, or TC to V
Ramp 0.2V to 1.8V
V

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Temperature Range −20˚C ≤ T

DD

DC and AC Electrical Characteristics

Unless otherwise specified, all limits guaranteed for VDD= 2.8V, GND = 0V, TJ= 25˚C. Boldface limits apply at temperature
range extremes of operating conditions.

Symbol Parameter Condition Min

(Note 7)

V

OUT

A, B
V

OUT

A, B

Positive Output Voltage Swing
A, B

Negative Output Voltage
Swing A, B

Sourcing 6mA, Tx_En = High
(Note 3)

Sinking 2mA,

= 0V 0.075 0.15 V

V

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Tx_En = High
(Note 3,4,5)

V

OUT

A, B
V

OS

Negative Output Voltage
Swing A,B

Input Offset Voltage (Note 6) 60 80 100 mV

Sinking 2mA, TX_EN = Low
(Note 3,4,5)

BW Bandwidth (−3dB) Rf = 50k, No External Frequency

Compensation

SR Output Slew Rate No External Frequency

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=0V

I

VHOME

I

BS

I

Tx_En

I

VfA

I

VfB

I

TC

Compensation, V

Current into V

Pin (Note 7)

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Current into BS Pin (Note 7)
Current into En Pin (Note 7)
Forward Bias Current Sources (Note 7) 7 10 13 µA

Temperature Compensation

(Note 7) 7 10 13 µA

Current Source

I

Vf-TC

Match

Current Source Matching ITC/I

ITC/I

VfA
VfB

(Note 7)

V

LOW

BS or Tx_En Logic Low Input

(Note 7) 0.8 V

Level

V

HIGH

BS or Tx_En Logic High Input

(Note 7) 1.8 V

Level

I

SD

V

RD

t

d: Tx_En

Supply Current in Shutdown Tx_En = 0V 0.15
Vramp Deadband (Note 7) 160 200 mV
Output Delay: Tx_En to

Output

I

DD

V
A,B

OUT

Positive Supply Current V

OUT=VDD/2

(Note 6) 1.1 1.8 mA

Threshold Select Voltages Tx_En = High, V

(Note 3, 4, and 5)

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=2V

2.6 2.7 V

3 5.5 V/µs

1.60 2 2.40 V

Typ

(Note 8)

Max

(Note 7)

0.06 0.15 V

>

1 MHz

<
<
<

±

2%

±

12%

<

3.5 6 µs

<

<

T

85˚C

J

0V to 5V

0V to 2V

≤ 85˚C

J

Units

5 µA
5 µA
5 µA

5 µA

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DC and AC Electrical Characteristics (Continued)

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 specific performance is not guaranteed. For guaranteed specifications and the test conditions, see the Electrical Characteristics.

Note 2: Human Body Model (HBM) is 1.5kΩ in series with 100pF.
Note 3: The output is not short circuit protected internally. External protection is necessary to prevent overheating and destruction or adverse reliability.
Note 4: Transients and spikes during V
Note 5: No overshoot above100mVoccurs when Tx_En is switched high to low or low to high. The overshoot is influenced by the external compensation capacitor.
Note 6: Tested in closed loop configuration.
Note 7: All limits are guaranteed by design or statistical analysis.
Note 8: Typical values represent the most likely parametric norm.

on transition are allowed only as described in the diagram.

DD

Ordering Information

Package Part Number Packaging Marking Transport Media NSC

Drawing

16-Pin LLP

LMV248LQ LMV248 1k Units Tape and Reel

LMV248LQX LMV248 4.5k Units Tape and Reel

LQA16A

LMV248

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Typical Performance Characteristics

LMV248

Error Amp Closed Loop Gain and Phase

(Rf=R

= 137k, AV−2.8)

COMP

Error Amp Open Loop Gain and Phase

(Rf=R

= 137k, AV−2.8)

COMP

10137203

I

SUPPLY

vs. V

DD

10137205 10137206

Voltage Drop (Sinking)

VfA or VfB vs. Ramp Output Fallback Voltage Out A or Out B vs. V

10137204

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10137207 10137208

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Typical Performance
Characteristics

Voltage Drop (Sourcing)

(Continued)

Block Diagram

LMV248

10137209

FIGURE 2.

10137210

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Application Section

Pin Description

LMV248

See

Figure 1

for the basics of a typical LMV248 dual band

Figure 2

internal architecture

for a simplified block diagram of the LMV248’s

See

application.

TABLE 1.

Pin Name Description

Power Supply 5, 6 GND Power Ground; both pins must be tied together.

9,11, 13 V

DD

Digital Inputs 1 BS Selects the RF detector input (VfA or VfB) and the corresponding output

2 Tx_En A HIGH input enables the input and output amplifiers (VfA and Out_A or

Analog Inputs 10 VfA Detector diodes for the RF power detector are connected here. An

12 VfB

14 TC The reference diode used for temperature compensation of the VfA and

15 Ramp Sets the RF output power level. The useful input voltage range is from

16 V

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Compensation 7 Comp1 Connect an external RC network here for overall loop compensation and

8 Comp2

Outputs 4 Out A A rail-to-rail output capable of sourcing is 6mA, sinking 2mA, with less

3 Out B

Note 9: All inputs and outputs are referenced to GND, except VfA, VfB, and TC, which are referenced to VDD.
Note 10: For the digital inputs, a LOW is ≤ 0.8V and HIGH is ≥ 1.8V.
Note 11: RF power detection is usually via a RF detector diode and a RF power coupler.

Positive Supply Voltage

amplifier (Out_A or Out_B) enabled when the Tx_En is HIGH. The
compensation is also connected to the correct amplifier automatically.
A HIGH input enables Out_A.
A LOW input enables Out_B.
The other unselected output is held close to GND.

VfB and Out_B) selected by the band select pin, BS.

internal switch connects a 10µA current sink to the input pin selected by
BS to bias the detector diode. This signal is referenced to V

DD

Notes 9 and 11).

VfB RF power signals is connected here. Internally, a 10µA current sink
connects to this pin to bias the reference diode. This signal is referenced

. (See notes 9 and 11).

to V

DD

0.2V to 1.8V, although voltages from 0V to V

are allowed. An internal

DD

filter with a corner frequency of approximately 1.6MHz smooths the
Ramp signal, to eliminate step discontinuities from the baseband DAC’s
output.

Sets the desired minimum output voltage of the controller (selected by
BS) to the threshold voltage of the RF power amplifier. This reduces
ramp up time, since a smaller voltage range is slewed across. The
recommended input voltage range is from 0V to 2V.

to control the closed loop frequency response. In most cases this
network will be simply a capacitor. Conventional loop stability techniques
can be used in selecting this network, such as Bode plots.

than 200mV drop including over temperature. The output is free from
glitches when enabled by Tx_En. When an output is not selected by BS,
it is close to GND. When Tx_En is low, output voltages are near GND.

. (See

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Application Section (Continued)

The LMV248 as a RF Power Amplifier (PA) Controller

The LMV248, a member of National Semiconductor’s family
of RF power amplifier (PA) power controllers, is used to
regulate the RF transmit power in TDMA (GSM, EGSM,
PCN, PCS AND DCS) mobile phones. Capable of controlling
up to two RF output amplifiers and of triple band operation
(GSM, DCS, and PCS) the device supports both bipolar and
FET RF power amplifiers including Silicon BJT,CMOS, SiGe
HBT, and GaAs HBT.

Figure 1

application. The key components are:

•

•

•

•

•

The block diagram in
architecture. The LMV248 contains input filters and condi­tioning amplifiers, an input summing network, detector bias­ing current source, error amplifier, output band select func­tion, and output drivers.

Power Supplies

The LMV248 supports a single supply with the battery volt­age at V

Digital Input Signals:

The LMV248 has two digital control signals:

•

•

The band select pin, BS, selects which band (i.e which
output and input channel) is active. A high enables Out_A, a
low enables Out_B. The transmit enable pin, Tx_En, is used
to enable the BS selected output during transmit (Tx) slots
and disable the outputs during receive (Rx) slots. Disabling
the output during the receive (Rx) slot shuts down the
LMV248’s output stages and the RF power amplifiers, con­serving battery power. A high input on the transmit enable
signal, Tx_En, brings the amplifier out of shutdown within
about 4µs. The output is glitch-free when enabled by this pin.

When an output is either not selected by BS or Tx_En is low,
its level is near GND. Internally, the band select pin, BS,
selects the correct input line and output amplifier,and places
the external compensation network across the active ampli­fier using analog switches.

Error Amplifier/Loop Compensation

The error amplifier (A1) controls the overall loop regulation
and response. Frequency compensation and stabilization of
the RF output power regulating loop is accomplished by a
capacitor (or resistor/capacitor network) across Comp1 and
Comp2 of the LMV248. This external network sets the
closed loop frequency response. In most cases this network
will simply be a capacitor. Conventional loop stability tech­niques can be used in selecting this network, such as Bode
plots.

Analog Inputs

At VfA and VfB are voltages proportional to the RF power
output of channel A and channel B respectively. Each of
these signals is derived from the RF output power via a RF

shows the basics of a typical LMV248 dual band

Two power amplifiers, usually for the GSM or DCS/PCS
bands.

RF directional couplers where two single or one dual
channel RF coupler could be used.

Up to three Schottky RF detector diodes, one for each
directional coupler output and one for temperature com­pensation.

A RF diplexer.
A dual or tri-band antenna.

Figure 2

.

DD

shows the LMV248’s internal

Transmit enable signal, Tx_En.
Band select signal, BS.

directional coupler a capacitor and a Schottky RF detector
diode. A single two-channel RF coupler could be used in­stead of the two single-channel RF couplers shown in

1

.

Figure

If only one input and output is needed, just connect BS high
or low and use the selected channel. At the TC input, a
reference diode identical to the detector diodes, and ther­mally coupled to them, is used for temperature compensa­tion of the VfA and VfB signals.

VfA, VfB and TC are referenced to V

. A 10µA current sink

DD

internal to the LMV248 connects to the VfA, VfB and TC pins
to bias the diodes. The quiescent voltage on all three pins is
one diode drop below V

. The actual Ramp input value sets

DD

the RF output power. The recommended Ramp voltage
range for RF power control is 0.2V to 1.8V. The Ramp input
will tolerate voltages from 0V to V

without malfunction or

DD

damage. This signal usually comes from the baseband con­troller’s DAC (digital to analog converter), its shape being
defined by the relevant GSM, PCN, or DCS standard.

The Ramp input does not change the output level from the
idle level set by V

until the level reaches about 200mV,

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so offset voltages in the DAC or amplifier supplying the
Ramp signal will not cause excess RF signal output and
increased power consumption. An internal RC filter with a
corner frequency of approximately 1.6MHz smooths the
Ramp signal, to eliminate step discontinuities at the base­band DAC’s output. Ramp is ground referenced, so supply
variations are rejected.

V

is used to set the output selected by BS to the

HOME

threshold voltage of the RF power amplifier. The variable
V

voltage level supports different PAShut off thresholds

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as well as boost output voltage to minimize phase delay at
low power levels. The V

voltage can be derived from a

HOME

reference, resistive voltage divider, or DAC output. The rec­ommended V
to 2V. The V

voltage range for threshold control is 0V

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input will tolerate voltages from 0V to V

HOME

DD

without malfunction or damage. The minimum output voltage
at Out_A or Out_B set by V
V

HOME.VHOME

is ground referenced. V

is approximately 3.0 x

HOME

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does not affect

the minimum voltage of the output not selected by BS.
For maximum performance a fine adjust is needed for

V

, since each individual RF power amplifier’s threshold

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voltage is slightly different from the nominal datasheet value.

Analog Outputs

Outputs Out_A and Out_B are driven by rail-to-rail amplifiers
capable of both sourcing and sinking. Either output can
source 6mA and sink 2mA with less than 200mV voltage
drop over recommended operating conditions. The output is
free from glitches when enabled by Tx_En. When an output
is not selected by BS, its level is near GND.

Understanding the LMV248
Input Structure

The LMV248 simplified block diagram of

Figure 2

shows the
IC’s internal structure. Input VfA goes through a resistor
(approximately 48.5kΩ) and analog switch to the inverting
input of the error amplifier A1. Input VfB goes through a
different resistor (also approximately 48.5kΩ) and analog
switch to the inverting input of the error amplifier A1. These
two analog switches are controlled by BS. VfA is selected
when BS is high and VfB is selected when BS is low. The
temperature compensation signal, TC, goes through a series
resistance of about 48.5kΩ, to the non-inverting input of the
error amplifier A1. This way the relatively large static DC
offset of the input signal is mostly removed from the differ­ential signal to be amplified by A1, and the temperature

LMV248

www.national.com7

Application Section (Continued)

dependency of the external detector diodes is cancelled.

LMV248

(Adding the temperature correction to the non-inverting ter­minal is identical to subtracting the temperature correction
from the inverting terminal). The 10µA current sinks con­nected to the signal paths for VfA, VfB, and TC provide a
bias current for the detector and temperature compensation
diodes. An approximate 200mV deadband for the Ramp
signal is preset.

Ramp Signal

The Ramp signal, which is positive going and ground refer­enced, is the reference for the closed loop RF output control.
The Ramp signal is smoothed by internal filter with a corner
frequency of approximately 1.6MHz, formed from a 20kΩ
resistor and 5pF capacitor. This filter eliminates step discon­tinuities at the baseband DAC’s output. Transconductance
amplifier A2 provides current sinking proportional to the
Ramp signal.

Since the output of A2 connects to the inverting terminal of
A1, A1 draws current from VfA or VfB through the 48.5kΩ
series resistance previously mentioned. This reduces the
voltage seen at the inverting terminal by the voltage drop
across the 48.5kΩ series resistance. The transconductance
of A2 is 1/(20kΩ). The net differential signal between the
non-inverting and inverting terminals of the error amplifier is

2.42 x Ramp-(Vf-TC). This means that the average (Vf-TC)
will be regulated to 2.42 x Ramp and that we want to choose
the RF directional coupler so that the peak RF detector
output at the maximum Ramp satisfies: (Peak Vf)-TC ≤ 2.42
x (maximum Ramp). See “Selecting Coupler/Detector” in the
next section. Note that the recommended maximum Ramp
≤ 2V.

V

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Amplifier A3 and the diode D1 at its output clamp the low
value of the active output to the value set by V
ever the outputs are enabled by Tx_En. V
the inverting input of amplifier A3. The non-inverting input of
amplifier A3 connects to the active output selected by BS,
selection being done by analog switches. Also connecting to
the non-inverting input of amplifier A3 is a voltage divider.
This makes the equation for the minimum output voltage 3.0
xV

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.

Outputs

The output amplifiers A4 and A5 are rail-to-rail complemen­tary MOS output stages using Class AB control, and capable
of both sourcing and sinking current. The output amplifier not
selected by BS is disabled; both output amplifiers are dis­abled when Tx_En is low. This conserves power.

The single compensation/stabilization network across
Comp1 and Comp2 is switched across the correct output
amplifier by analog switches controlled by BS.

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, when-

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connects to

Typical LMV248 Configurations:

10137211

FIGURE 3. One Input, One Output (A)

10137212

FIGURE 4. One Input, One Output (B)

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10137213

FIGURE 5. One Input, Two Outputs

Application Section (Continued)

The LMV248 has separate inputs for the coupler/detector
feedback signal(s). These may be combined as a single
input when using a single coupler/detector that accommo­dates both RF bands. When the two are combined as shown
in

Figure 5

maintain correct temperature compensation characteristics
for the applications circuit, an external biasing resistor, R'
should be added externally. For this arrangement, VfA, VfB,
and TC all are returned to a common supply, V

Selecting Coupler/Detector
Coupler Calculations:

The applied Ramp voltage controls the RF power output.
Because of this the maximum Ramp voltage sets the mini­mum attenuation that is allowed in the direction coupler used
to sense output power.

The basic equation is;

For peak detection it is;

The coupling factor, at maximum power, is defined as C

or,
Cf=(V

peak power
The limit conditions for the maximum ramp and max power

out is,

internal current sources are placed in parallel. To

.

CC

2

/R

O

xRO) for couplers that sense

rampmax

)2/2x(P

P

O=Vrms

outmax

f

= 2.0V

= 2Watts

=50Ω
= 10 x log10[(1/2)(V
= −16.98dB

rampmax

)2/P

outmaxxRO

)]

C
C

V
P
R

fdB
fdB

rampmax
outmax
O

Attenuation in the directional coupler should be at least

−17dB, to assure maximum power out.

General Device Equations
Calculation:

Let Vf be VfA or VfB as selected by BS. Let RVf be the
external series resistance from Vf to the Detector diode.

Voltage at the non-inverting terminal of A1 V

= TC, since

NI

current into A2’s input is small.
Voltage at the inverting terminal of A1 V

INV

=Vf-

[Ramp/(20kΩ)] x (RVf + 48.5kΩ)
Assuming the external series resistance for VfA and VfB is

<<

48.5kΩ:

Voltage at the inverting terminal of A1 V

= Vf – 2.42 x

INV

Ramp
Differential voltage at A1 inputs = V

NI-VINV

= TC - (Vf - 2.42

x Ramp) = 2.42 x Ramp - (Vf - TC).
Closed loop regulation of RF output power will force the

average differential voltage at A1 inputs to approach zero:

Average

Including the V
the equation for the VfA, B vs. V

VfA, B = 2.42 x (V

deadband and the device offset voltage,

ramp

-200mV) + TC - 80mV, all variables

ramp

relationship becomes:

ramp

being ground referenced DC voltages.

LMV248

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Application Section (Continued)

LMV248

Timing Diagram

Time Slot Enabled

#

1

Timing Diagram#2

Tx/Rx Enabled

10137216

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10137217

Physical Dimensions inches (millimeters)

unless otherwise noted

LMV248 Dual Band GSM Power Controller

NS Product Number LQA16A

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