LMV227 Production RF Tested, RF Power Detector for CDMA and WCDMA General Description Features The LMV227 is a 30 dB RF power detector intended for use in CDMA and WCDMA applications. The device has an RF frequency range from 450 MHz to 2 GHz. It provides an accurate temperature and supply compensated output voltage that relates linearly to the RF input power in dBm. The circuit operates with a single supply from 2.7V to 5V. The LMV227 has an integrated filter for low-ripple average power detection of CDMA signals with 30 dB dynamic range. Additional filtering can be applied using a single external capacitor. The LMV227 has an RF power detection range from -30 dBm to 0 dBm and is ideally suited for direct use in combination with resistive taps. The device is active for Enable = HI, otherwise it goes into a low power consumption shutdown mode. During shutdown the output will be LOW. The output voltage ranges from 0.2V to 2V and can be scaled down to meet ADC input range requirements. The output signal bandwidth can optionally be lowered externally as well. n n n n n 30 dB linear in dB power detection range Output voltage range 0.2 to 2V Logic low shutdown Multi-band operation from 450 MHz to 2000 MHz Accurate temperature compensation Applications n n n n CDMA RF power control WCDMA RF power control CDMA2000 RF power control PA modules Typical Application 20118101 © 2006 National Semiconductor Corporation DS201181 www.national.com LMV227 Production RF Tested, RF Power Detector for CDMA and WCDMA July 2006 LMV227 Absolute Maximum Ratings (Note 1) Storage Temperature Range If Military/Aerospace specified devices are required, please contact the National Semiconductor Sales Office/ Distributors for availability and specifications. Junction Temperature (Note 3) −65˚C to 150˚C 150˚C Max Mounting Temperature Infrared or convection (20 sec) 235˚C Supply Voltage VDD - GND 6.0V Max Operating Ratings (Note 1) ESD Tolerance (Note 2) Human Body Model Machine Model Supply Voltage 2000V 2.7V to 5.5V Temperature Range 200V −40˚C to +85˚C 2.7 DC and AC Electrical Characteristics Unless otherwise specified, all limits are guaranteed to VDD = 2.7V; TJ = 25˚C. Boldface limits apply at temperature extremes. (Note 4) Symbol IDD Parameter Supply Current Typ Max Units Active mode: RFIN/EN = VDD (DC), No RF Input Power Present. Condition Min 4.9 7 8 mA Shutdown: RFIN/EN = GND (DC), No RF Input Power Present. 0.6 4.5 µA 0.8 V VLOW EN Logic Low Input Level (Note 6) VHIGH EN Logic High Input Level (Note 6) ton Turn-on- Time No RF Input Power Present 2.1 tr Rise Time (Note 7) Step from No Power to 0 dBm Applied 4.5 IEN Current into RFIN/EN Pin PIN Input Power Range (Note 5) Logarithmic Slope (Note 8) 1.8 µs µs 1 900 MHz µA 0 -30 dBm -43 -13 dBV 43.3 1800 MHz 43.9 1855 MHz 36 1900 MHz Logarithmic Intercept (Note 8) V 43.5 51 mV/dB −33 dBm 44.0 2000 MHz 43.2 900 MHz −46.7 1800 MHz −44.1 1855 MHz −56 −44.3 1900 MHz −42.8 2000 MHz −43.7 VOUT Output Voltage No RF Input Power Present 208 350 mV ROUT Output Impedance No RF Input Power Present 20.3 29 34 kΩ en Output Referred Noise RF Input = 1800 MHz, −10 dBm, Measured at 10 kHz 700 Variation over Temperature 900 MHz, RFIN = 0 dBm Referred to 25˚C +0.64 −1.07 1800 MHz, RFIN = 0 dBm Referred to 25˚C +0.09 −0.86 1900 MHz, RFIN = 0 dBm Referred to 25˚C +0 −0.69 2000 MHz, RFIN = 0 dBm Referred to 25˚C +0 −0.86 www.national.com 2 nV/ dB Unless otherwise specified, all limits are guaranteed to VDD = 5.0V; TJ = 25˚C. Boldface limits apply at temperature extremes. (Note 4) Symbol IDD Parameter Supply Current Condition Min Typ Max Units Active Mode: RFIN/EN = VDD (DC), No RF Input Power Present. 5.3 7 9 mA Shutdown: RFIN/EN = GND (DC), No RF Input Power Present. 0.49 4.5 µA 0.8 V VLOW EN Logic Low Input Level (Note 6) VHIGH EN Logic High Input Level (Note 6) ton Turn-on- Time No RF Input Power Present 2.1 µs tr Rise Time (Note 7) Step from No Power to 0 dBm Applied 4.5 µs IEN Current Into RFIN/EN Pin PIN, MIN Input Power Range (Note 5) Logarithmic Slope (Note 8) Logarithmic Intercept (Note 8) 1.8 V 1 µA -30 0 dBm -43 -13 dBV 900 MHz 43.6 1800 MHz 44.5 1900 MHz 44.5 2000 MHz 43.7 900 MHz -48.1 1800 MHz -45.6 1900 MHz -44.2 2000 MHz -45.6 mV/dB dBm VOUT Output Voltage No RF Input Power Present 211 400 mV ROUT Output Impedance No RF Input Power Present 23.4 29 31 kΩ en Output Referred Noise RF Input = 1800 MHz, −10 dBm, Measured at 10 kHz 700 Variation over Temperature 900 MHz, RFIN = 0 dBm Referred to 25˚C +0.89 −1.16 1800 MHz, RFIN = 0 dBm Referred to 25˚C +0.3 −0.82 1900 MHz, RFIN = 0 dBm Referred to 25˚C +0.34 −0.63 2000 MHz RFIN = 0 dBm Referred to 25˚C +0.22 −0.75 nV/ dB 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: 1.5 kΩ in series with 100 pF. Machine model, 0Ω in series with 100 pF. Note 3: The maximum power dissipation is a function of TJ(MAX) , θJA and TA. The maximum allowable power dissipation at any ambient temperature is PD = (TJ(MAX) - TA)/θJA. All numbers apply for packages soldered directly into a PC board Note 4: Electrical Table values apply only for factory testing conditions at the temperature indicated. Factory testing conditions result in very limited self-heating of the device such that TJ = TA. No guarantee of parametric performance is indicated in the electrical tables under conditions of internal self-heating where TJ > TA. Note 5: Power in dBV = dBm −13 when the impedance is 50Ω. Note 6: All limits are guaranteed by design or statistical analysis Note 7: Typical values represent the most likely parametric norm. Note 8: Device is set in active mode with a 10 kΩ resistor from VDD to RFIN/EN. RF signal is applied using a 50Ω RF signal generator AC coupled to the RFIN/EN pin using a 100 pF coupling capacitor. 3 www.national.com LMV227 5.0 DC and AC Electrical Characteristics LMV227 Connection Diagram 6-pin LLP 20118102 Top View Pin Descriptions Pin Power Supply Output Name Description 4 VDD Positive supply voltage 1 GND Power ground 3 RFIN/EN 6 OUT DC voltage determines enable state of the device (HIGH = device active). AC voltage is the RF input signal to the detector (beyond 450 MHz). The RFIN/EN pin is internally terminated with 50Ω in series with 45 pF. Ground referenced detector output voltage (linear in dBm) Ordering Information Package 6-pin LLP Part Number LMV227SD LMV227SDX Package Marking Transport Media 2k Units Tape and Reel A88 9k Units Tape and Reel Note: This product is offered both with leaded and lead free bumps. Block Diagram 20118103 www.national.com 4 NSC Drawing SDB06A LMV227 Typical Performance Characteristics Unless otherwise specified, VDD = 2.7V, TJ = 25˚C. Supply Current vs. Supply Voltage Output Voltage vs. RF Input Power 20118104 20118105 Output Voltage and Log Conformance vs. RF Input Power @ 1800 MHz Output Voltage and Log Conformance vs. RF Input Power @ 900 MHz 20118106 20118107 Output Voltage and Log Conformance vs. RF Input Power @ 2000 MHz Output Voltage and Log Conformance vs. RF Input Power @ 1900 MHz 20118108 20118109 5 www.national.com LMV227 Typical Performance Characteristics Unless otherwise specified, VDD = 2.7V, TJ = 25˚C. (Continued) Logarithmic Slope vs. Frequency Logarithmic Intercept vs. Frequency 20118111 20118110 Output Variation vs. RF Input Power Normalized to 25˚C @ 1800 MHz Output Variation vs. RF Input Power Normalized to 25˚C @ 900 MHz 20118112 20118113 Output Variation vs. RF Input Power Normalized to 25˚C @ 2000 MHz Output Variation vs. RF Input Power Normalized to 25˚C @ 1900 MHz 20118114 www.national.com 20118115 6 LMV227 Typical Performance Characteristics Unless otherwise specified, VDD = 2.7V, TJ = 25˚C. (Continued) RF Input Impedance vs. Frequency @ Resistance and Reactance PSRR vs. Frequency 20118135 20118136 7 www.national.com LMV227 Application Notes CONFIGURING A TYPICAL APPLICATION The LMV227 is a power detector intended for CDMA and WCDMA applications. Power measured on its input translates to a DC voltage on the output through a linear-in-dB response. The detector is especially suited for power measurements via a high-resistive tap, which eliminates the need for a directional coupler. In order to match the dynamic output range of the power amplifier (PA) with the dynamic range of the LMV227’s input, the high resistive tap needs to be configured correctly. Input Attenuation The constant input impedance of the device enables the realization of a frequency independent input attenuation to adjust the LMV227’s dynamic range to the dynamic range of the PA. Resistor R1 and the 50Ω input resistance of the device realize this attenuation (Figure 1). To minimize insertion loss, resistor R1 needs to be sufficiently large. The following example demonstrates how to determine the proper value for R1. Suppose the useful output power of the PA ranges up to +31 dBm and the LMV227 can handle input power levels up to 0 dBm. Hence, R1 should realize a minimum attenuation of 31 - 0 = 31 dB. The attenuation realized by R1 and the effective input resistance RIN of the detector equals: 20118133 FIGURE 1. Typical Application The output voltage is linear with the logarithm of the input power, often called "linear-in-dB". Figure 2 shows the typical output voltage versus PA output power of the LMV227 setup as depicted in Figure 1. (1) Solving this expression for R1, using that RIN = 50Ω, yields: (2) In Figure 1, R1 is set to 1800Ω resulting in an attenuation of 31.4 dB DC and AC Behavior of the RFIN/EN Pin The LMV227 RFIN/EN pin has 2 functions combined: • Shutdown functionality • Power detection The capacitor C and the resistor R2 of Figure 1 separate the DC shutdown functionality from the AC power measurement. The device is active when Enable = HI, otherwise it goes into a low power consumption shutdown mode. During shutdown the output will be LOW. Capacitor C should be chosen sufficiently large to ensure a corner frequency far below the lowest input frequency to be measured. The corner frequency can be calculated using: 20118116 FIGURE 2. Typical Power Detector Response, VOUT vs. PA Output Power OUTPUT RIPPLE DUE TO AM MODULATION A CDMA modulated carrier wave generally contains some amplitude modulation that might disturb the RF power measurement used for controlling the PA. This section explains the relation between amplitude modulation in the RF signal and the ripple on the output of the LMV227. Expressions are provided to estimate this ripple on the output. The ripple can be further reduced by connecting an additional capacitor to the output of the LMV227 to ground. Estimating Output Ripple The CDMA modulated RF input signal of Figure 3 can be described as: (4) VIN(t) = VIN [1 + µ(t)] cos (2 · π · f · t) In which the amplitude modulation µ(t) can be between −1 and 1. (3) Where RIN = 50Ω, CIN = 45 pF typical. With R1 = 1800Ω and C is 100 pF, this results in a corner frequency of 2.8 MHz www.national.com 8 LMV227 Application Notes (Continued) 20118117 20118118 FIGURE 3. AM Modulated RF Signal FIGURE 4. VOUT vs. RF Input Power PIN The ripple observed on the output of the detector equals the detectors response to variation on the input due to AM modulation (Figure 3). This signal has a maximum amplitude VIN(1+µ) and a minimum amplitude VIN(1−µ), where 1+µ can be maximum 2 and 1−µ can be minimum 0. The ripple can be described with the formula: Besides the ripple due to AM modulation, the log- conformance error contributes to a variation in VOUT. For details see the typical performance characteristics curves. The output voltage variation ∆VOUT thus is always the same for RF input signals which fall within the linear range (in dB) of the detector plus the log-conformance error: (7) ∆VO = VY · ∆PIN + Log Conformance Error In which VY is the slope of the curve. The log-conformance error is usually much smaller than the ripple due to AM modulation. In case of the LMV227, VY = 40 mV/dB. With ∆PIN = 5 dB for CDMA, the ∆VO = 200 mVPP. This is valid for all VOUT. (5) where VY is the slope of the detection curve (Figure 4) and µ is the modulation index. Equation 5 can be reduced to: Output Ripple With Additional Filtering The calculated result above is for an unfiltered configuration. When a low pass filter is used by shunting a capacitor of e.g. COUT = 1.5 nF at the output of the LMV227 to ground, this ripple is further attenuated. The cut-off frequency follows from: (6) Consequently, the ripple is independent of the average input power of the RF input signal and only depends on the logarithmic slope VY and the ratio of the maximum and the minimum input signal amplitude. For CDMA, the ratio of the maximum and the minimum input signal amplitude modulation is typically in the order of 5 to 6 dB, which is equivalent to a modulation index µ of 0.28 to 0.33. A further understanding of the equation above can be achieved via the knowledge that the output voltage VOUT of the LMV227 is linear in dB, or proportional to the input power PIN in dBm. As discussed earlier, CDMA contains amplitude modulation in the order of 5 to 6 dB. Since the transfer is linear in dB, the output voltage VOUT will vary linearly over about 5 to 6 dB in the curve (Figure 4). (8) With the output resistance of the LMV227 RO = 19.8 kΩ typical and COUT = 1.5 nF, the cut-off frequency equals fC = 5.36 kHz. A 100 kHz AM signal then gets attenuated by 5.36/100 or 25.4 dB. The remaining ripple will be less than 20 mV. With a slope of 40 mV/dB this translates into an error of less than 0.5 dB. Output Ripple Measurement Figure 5 shows the ripple reduction that can be achieved by adding additional capacitance on the output of the LMV227. The RF signal of 900 MHz is AM modulated with a 100 kHz sinewave and a modulation index of 0.3. The RF input power is swept while the modulation index remains unchanged. Without addition capacitance the ripple is about 200 mVPP. Connecting a capacitor of 1.5 nF at the output to ground, results in a ripple of 12 mVPP. The attenuation with a 1.5 nF capacitor is then 20 · log (200/12) = 24.4 dB. This is very close to the number calculated in the previous paragraph. 9 www.national.com LMV227 Application Notes (Continued) All gain cell outputs are AM-demodulated with a peak detector and summed together. This results in a logarithmic function. The logarithmic range is about: 20 · n · log (A) where, n = number of gain cells A = gain per gaincell Figure 8 shows a logarithmic function on a linear scale and the piecewise approximation of the logarithmic function. 20118125 FIGURE 5. Output Ripple vs. RF Input Power 20118121 PRINCIPLE OF OPERATION The logarithmic response of the LMV227 is implemented by a de-modulating logarithmic amplifier as shown in Figure 6. The logarithmic amplifier consists of a number of cascaded linear gain cells. With these gain cells, a piecewise approximation of the logarithmic function is constructed. FIGURE 8. Log-Function on Lin Scale Figure 9 shows a logarithmic function on a logarithmic scale and the piecewise approximation of the logarithmic function. 20118122 20118119 FIGURE 9. Log-Function on Log Scale FIGURE 6. Logarithmic Amplifier The maximum error for this approximation occurs at the geometric mean of a gain section, which is e.g. for the third segment: Every gain cell has a response according to Figure 7. At a certain threshold (EK), the gain cell starts to saturate, which means that the gain drops to zero. The output of gain cell 1 is connected to the input of gain cell 2 and so on. The size of the error increases with distance between the thresholds. 20118120 FIGURE 7. Gain Cell www.national.com 10 bandwidth will drop when the parasitic capacitance of the resistance is to high, which will cause a significant attenuation drop at the GSM frequencies and can cause non-linear behavior. To reduce the parasitic capacitance across resistor R1, it can be composed of several resistor in series in stead of a single component. (Continued) LAYOUT CONSIDERATIONS For a proper functioning part a good board layout is necessary. Special care should be taken for the series resistance R1 (Figure 1) that determines the attenuation. This series resistance should have a sufficiently high bandwidth. The 11 www.national.com LMV227 Application Notes LMV227 Production RF Tested, RF Power Detector for CDMA and WCDMA Physical Dimensions inches (millimeters) unless otherwise noted 6 Pin LLP NS Package Number SDB06A 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. For the most current product information visit us at www.national.com. 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. Life support devices or systems are devices or systems which, (a) are intended for surgical implant into the body, or (b) support or sustain life, and whose failure to perform when properly used in accordance with instructions for use provided in the labeling, can be reasonably expected to result in a significant injury to the user. 2. A critical component is any component of a life support device or system whose failure to perform can be reasonably expected to cause the failure of the life support device or system, or to affect its safety or effectiveness. BANNED SUBSTANCE COMPLIANCE National Semiconductor follows the provisions of the Product Stewardship Guide for Customers (CSP-9-111C2) and Banned Substances and Materials of Interest Specification (CSP-9-111S2) for regulatory environmental compliance. Details may be found at: www.national.com/quality/green. Lead free products are RoHS compliant. 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