LMV248 Dual Band GSM Power Controller General Description Features 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 PA shutdown. 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. n n n n n n n n n n Connection Diagram Typical Application Circuit Multi-band cellular operation (example: GSM, PCN) Support of GaAs HBT and bipolar technology Shutdown mode for power save in Rx slot (0.15µA) Integrated ramp filter Built-in current source for biasing Schottky diodes Pre-biasing of PA control gate voltage (VHOME) GPRS compliant External loop compensation Detector diode temperature compensation Miniature packaging: LLP-16: 4mm x 4mm x 0.8mm Applications n n n n n GSM mobile phone TDMA RF control Wireless LAN PC and PDA modules GPS navigation modules 16-Pin LLP 10137201 Top View 10137202 FIGURE 1. © 2001 National Semiconductor Corporation DS101372 www.national.com LMV248 Dual Band GSM Power Controller September 2001 LMV248 Absolute Maximum Ratings (Note 1) −40˚C < TJ < 85˚C Operating Temperature If Military/Aerospace specified devices are required, please contact the National Semiconductor Sales Office/ Distributors for availability and specifications. 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 Operating Ratings (Note 1) 100V Supply Voltage Supply Voltage VDD to GND VDD to GND 5.5V Input Voltage Range VfA, VfB, or TC to GND Ramp VfA, VfB, or TC to VDD 10V 0.2V to 1.8V VHOME 0 to VDD Junction Temperature 0V to 5V Ramp 0 to VDD VHOME 2.5V to 5V Input Voltage 0V to 2V −20˚C ≤ TJ ≤ 85˚C Temperature Range 150˚C max 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 VOUT A, B Positive Output Voltage Swing A, B Sourcing 6mA, Tx_En = High (Note 3) VOUT A, B Negative Output Voltage Swing A, B Sinking 2mA, Tx_En = High (Note 3,4,5) VOUT A, B Negative Output Voltage Swing A,B Sinking 2mA, TX_EN = Low (Note 3,4,5) Min (Note 7) Typ (Note 8) 2.6 2.7 VHOME = 0V VOS Input Offset Voltage (Note 6) BW Bandwidth (−3dB) Rf = 50k, No External Frequency Compensation SR Output Slew Rate No External Frequency Compensation, VHOME = 0V IVHOME Current into VHOME Pin (Note 7) IBS Current into BS Pin (Note 7) ITx_En Current into En Pin (Note 7) IVfA IVfB Forward Bias Current Sources (Note 7) 7 ITC Temperature Compensation Current Source (Note 7) 7 IVf-TC Current Source Matching ITC/IVfA ITC/IVfB (Note 7) VLOW BS or Tx_En Logic Low Input Level (Note 7) VHIGH BS or Tx_En Logic High Input Level (Note 7) ISD Supply Current in Shutdown Tx_En = 0V VRD Vramp Deadband (Note 7) td: Tx_En Output Delay: Tx_En to Output Match 60 0.075 0.15 V 0.06 0.15 V 80 100 MHz 5.5 V/µs <5 <5 <5 µA 10 13 µA 10 13 µA ± 2% ± 12% Positive Supply Current VOUT = VDD/2 (Note 6) Tx_En = High, VHOME = 2V (Note 3, 4, and 5) 2 1.60 <5 200 3.5 Threshold Select Voltages µA µA V V 0.15 VOUT A,B mV >1 1.8 160 Units V 0.8 IDD www.national.com 3 Max (Note 7) µA mV 6 µs 1.1 1.8 mA 2 2.40 V (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 VDD on transition are allowed only as described in the diagram. Note 5: No overshoot above 100mV occurs 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. Ordering Information Package 16-Pin LLP Part Number Packaging Marking LMV248LQ LMV248 1k Units Tape and Reel LMV248LQX LMV248 4.5k Units Tape and Reel 3 Transport Media NSC Drawing LQA16A www.national.com LMV248 DC and AC Electrical Characteristics LMV248 Typical Performance Characteristics Error Amp Closed Loop Gain and Phase (Rf = RCOMP = 137k, AV −2.8) Error Amp Open Loop Gain and Phase (Rf = RCOMP = 137k, AV −2.8) 10137203 10137204 ISUPPLY vs. VDD Voltage Drop (Sinking) 10137205 10137206 VfA or VfB vs. Ramp Output Fallback Voltage Out A or Out B vs. VHOME 10137207 www.national.com 10137208 4 LMV248 Typical Performance Characteristics (Continued) Voltage Drop (Sourcing) 10137209 Block Diagram 10137210 FIGURE 2. 5 www.national.com LMV248 See Figure 2 for a simplified block diagram of the LMV248’s internal architecture Application Section Pin Description See Figure 1 for the basics of a typical LMV248 dual band application. TABLE 1. Pin Power Supply Digital Inputs Analog Inputs Compensation Outputs Name Description 5, 6 GND Power Ground; both pins must be tied together. 9,11, 13 VDD Positive Supply Voltage 1 BS Selects the RF detector input (VfA or VfB) and the corresponding output 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. 2 Tx_En A HIGH input enables the input and output amplifiers (VfA and Out_A or VfB and Out_B) selected by the band select pin, BS. 10 VfA 12 VfB Detector diodes for the RF power detector are connected here. An internal switch connects a 10µA current sink to the input pin selected by BS to bias the detector diode. This signal is referenced to VDD. (See Notes 9 and 11). 14 TC The reference diode used for temperature compensation of the VfA and 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 to VDD. (See notes 9 and 11). 15 Ramp Sets the RF output power level. The useful input voltage range is from 0.2V to 1.8V, although voltages from 0V to VDD are allowed. An internal filter with a corner frequency of approximately 1.6MHz smooths the Ramp signal, to eliminate step discontinuities from the baseband DAC’s output. 16 VHOME 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. 7 Comp1 8 Comp2 Connect an external RC network here for overall loop compensation and 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. 4 Out A 3 Out B A rail-to-rail output capable of sourcing is 6mA, sinking 2mA, with less 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. 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. www.national.com 6 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 Figure 1. (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. 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 VDD. A 10µA current sink 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 VDD. The actual Ramp input value sets 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 VDD without malfunction or 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 VHOME until the level reaches about 200mV, 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. VHOME is used to set the output selected by BS to the threshold voltage of the RF power amplifier. The variable VHOME voltage level supports different PA Shut off thresholds as well as boost output voltage to minimize phase delay at low power levels. The VHOME voltage can be derived from a reference, resistive voltage divider, or DAC output. The recommended VHOME voltage range for threshold control is 0V to 2V. The VHOME input will tolerate voltages from 0V to VDD without malfunction or damage. The minimum output voltage at Out_A or Out_B set by VHOME is approximately 3.0 x VHOME. VHOME is ground referenced. VHOME does not affect the minimum voltage of the output not selected by BS. For maximum performance a fine adjust is needed for VHOME, since each individual RF power amplifier’s threshold 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 Figure 1 shows the basics of a typical LMV248 dual band application. The key components are: • 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. The block diagram in Figure 2 shows the LMV248’s internal 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 VDD. Digital Input Signals: The LMV248 has two digital control signals: • Transmit enable signal, Tx_En. • Band select signal, BS. 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 7 www.national.com LMV248 Application Section LMV248 Application Section Typical LMV248 Configurations: (Continued) dependency of the external detector diodes is cancelled. (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. VHOME 10137211 FIGURE 3. One Input, One Output (A) Amplifier A3 and the diode D1 at its output clamp the low value of the active output to the value set by VHOME, whenever the outputs are enabled by Tx_En. VHOME connects to 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 x VHOME. 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. 10137212 FIGURE 4. One Input, One Output (B) 10137213 FIGURE 5. One Input, Two Outputs www.national.com 8 LMV248 Application Section Vrampmax = 2.0V Poutmax = 2Watts (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 internal current sources are placed in parallel. To 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, VCC. 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; PO = Vrms2/RO RO = 50Ω CfdB = 10 x log10 [(1/2)(Vrampmax)2/Poutmax x RO)] CfdB = −16.98dB 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 VNI = TC, since current into A2’s input is small. Voltage at the inverting terminal of A1 VINV = 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 VINV = Vf – 2.42 x Ramp Differential voltage at A1 inputs = VNI - 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 Vramp deadband and the device offset voltage, the equation for the VfA, B vs. Vramp relationship becomes: VfA, B = 2.42 x (Vramp-200mV) + TC - 80mV, all variables being ground referenced DC voltages. For peak detection it is; The coupling factor, at maximum power, is defined as Cf or, Cf = (Vrampmax)2/2 x (Poutmax x RO) for couplers that sense peak power The limit conditions for the maximum ramp and max power out is, 9 www.national.com LMV248 Application Section (Continued) Timing Diagram #1 Time Slot Enabled 10137216 Timing Diagram #2 Tx/Rx Enabled 10137217 www.national.com 10 LMV248 Dual Band GSM Power Controller Physical Dimensions inches (millimeters) unless otherwise noted NS Product Number LQA16A LIFE SUPPORT POLICY NATIONAL’S PRODUCTS ARE NOT AUTHORIZED FOR USE AS CRITICAL COMPONENTS IN LIFE SUPPORT DEVICES OR SYSTEMS WITHOUT THE EXPRESS WRITTEN APPROVAL OF THE PRESIDENT AND GENERAL COUNSEL OF NATIONAL SEMICONDUCTOR CORPORATION. As used herein: 1. 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