Freescale Semiconductor, Inc. Order this document by MC3374/D . . . with single conversion circuitry including oscillator, mixer, IF amplifiers, limiting IF circuitry, and quadrature discriminator. The MC3374 is perfect for narrowband audio and data applications up to 75 MHz which require extremely low power consumption. Battery powered applications down to VCC = 1.1 V are possible. The MC3374 also includes an on–board voltage regulator, low battery detection circuitry, a receiver enable allowing a power down Sleep–Mode, two undedicated buffer amplifiers to allow simultaneous audio and data reception, and a comparator for enhancing FSK (Frequency Shift Keyed) data reception to 1200 baud. • Low Supply Voltage: VCC = 1.1 to 3.0 Vdc • • • • • • • • • • LOW VOLTAGE SINGLE CONVERSION FM RECEIVER SEMICONDUCTOR TECHNICAL DATA ARCHIVE INFORMATION Freescale Semiconductor, Inc... ARCHIVE INFORMATION Low Power Consumption: PD = 1.5 to 5.0 mW Input Bandwidth 75 MHz 32 Excellent Sensitivity: 0.5 µVrms for 12 dB SINAD 1 Voltage Regulator Available (Source Capability 3.0 mA) Receiver Enable to Allow Active/Standby Operation Low Battery Detection Circuitry FTB SUFFIX PLASTIC PACKAGE CASE 873 (Thin QFP) Self Biasing Audio Buffer Data Buffer FSK Data Shaping Comparator Standard 32–Lead QFP Surface Mount Package ORDERING INFORMATION Sleep–Mode is a trademark of Motorola, Inc. Device Tested Operating Temperature Range MC3374FTB TA = – 10° to +70°C Package TQFP–32 Simplified Block Diagram Data Data Osc Mixer Mixer Mixer 2nd IF Buffer Buffer 1st IF Dcpl In Out Dcpl In Out In Out 32 Osc Base 31 1 30 29 28 Data Buffer Mixer 2nd IF Osc Emit Isrc Dcpl 26 25 24 VCC3 1st IF 2 23 1st IF In Audio Buffer 3 IF Gnd 4 VCC2 5 Rec Audio 6 Voltage Reference 8 9 *Internal Connection, do not ground. Main Current Reference Quadrature Demodulator 10 11 Quad Demod *N/C Tank Gnd 12 13 20 Low Battery Detector 19 1.2 V Select 18 VCC Receiver Enable Comp. 22 Audio Buffer Out 21 Audio Buffer In Low Battery Detector Low Pass Filter Output Demodulator Decoupling 7 Buffer Quad Tank 27 14 Voltage Reference 15 17 Vreg 16 *N/C Comp Comp Rec Regulator I/P O/P Enable Reference Test This device contains 87 active transistors Motorola, Inc. 1996 MOTOROLA ANALOG IC DEVICEFor DATA More Information On This Product, Go to: www.freescale.com Rev 0 1 Freescale Semiconductor, Inc. MC3374 MAXIMUM RATINGS (Voltage with respect to Pins 4 and 10; TA = 25°C.) Pin Value Unit Supply Voltage Rating 18 5.0 Vdc RF Input Signal 31 1.0 Vrms Audio Buffer Input 21 1.0 Vrms Data Buffer Input 26 1.0 Vrms Comparator Input 13 1.0 Vrms Junction Temperature – 150 °C Storage Temperature – – 65 to +150 °C Device should not be operated at or outside these values. The “Recommended Operating Limits” provide for actual device operation. ARCHIVE INFORMATION Parameter Freescale Semiconductor, Inc... Pin Value Unit Supply Voltage 18 1.1 to 3.0 Vdc Receiver Enable Voltage 15 VCC Vdc 1.2 V Select Voltage 19 Open or VCC Vdc RF Input Signal Level 31 0.001 to 100 mVrms RF Input Frequency 31 0 to 75 MHz Intermediate Frequency (IF) – 455 kHz Audio Buffer Input 21 0 to 75 mVrms Data Buffer Input 26 0 to 75 mVrms Comparator Input 13 10 to 300 mVrms Ambient Temperature – –10 to 70 °C ELECTRICAL CHARACTERISTICS (VCC = 1.3 V, fo = 10.7 MHz, fmod = 1.0 kHz, Deviation = 3.0 kHz, TA = 25°C, Test Circuit of Figure 1, unless otherwise noted.) Characteristic Pin Min Typ Max Unit 5 + 18 + 24 5 + 18 + 24 – – 1.6 0.5 3.0 – mA µA 6 13 18 30 mVrms Noise Output (RF Input = 0 mV, 300 Hz – 5.0 kHz) 6 – 1.0 – mVrms Input for – 3.0 dB Limiting 31 – 0.6 – µVrms Mixer Input Resistance (Rp) 31 – 1.5 – kΩ Mixer Input Capacitance (Cp) 31 – 9.0 – pF – – 27 – dB Voltage Gain – 3.0 4.0 4.7 V/V Input Resistance 21 – 110 – kΩ Maximum Input for Undistorted Output (<5% THD) 21 – 64 – mVrms Maximum Output Swing (<5% THD) 22 – 690 – mVpp Output Resistance 22 – 780 – Ω Voltage Gain – 1.4 2.7 4.3 V/V Input Resistance 26 – 9.8 – MΩ Maximum Input for Undistorted Output (<5% THD) 26 – 100 – mVrms Maximum Output Swing (<5% THD) 27 – 800 – mVpp Output Resistance 27 – 690 – Ω OVERALL MC3374 PERFORMANCE Drain Current – Pin 15 = VCC (Enabled) Drain Current – Pin 15 = 0 Vdc (Disabled) Recovered Audio (RF Input = 10 µV) ā MIXER FIRST IF AMPLIFIER First IF Amp Voltage Gain AUDIO BUFFER DATA BUFFER 2 MOTOROLA ANALOG IC DEVICE DATA For More Information On This Product, Go to: www.freescale.com ARCHIVE INFORMATION RECOMMENDED OPERATING CONDITIONS Freescale Semiconductor, Inc. MC3374 ELECTRICAL CHARACTERISTICS (continued) (VCC = 1.3 V, fo = 10.7 MHz, fmod = 1.0 kHz, Deviation = 3.0 kHz, TA = 25°C, Test Circuit of Figure 1, unless otherwise noted.) Characteristic Pin Min Typ Max Unit Minimum Input for Triggering (RL = 100 kΩ) 13 – 7.0 – mVrms Maximum Input Frequency (RL = 100 kΩ) 13 – 25 – kHz Rise Time (10 – 90%; RL = 100 kΩ) 14 – 5.0 – µs Fall Time (90 – 10%; RL = 100 kΩ) 14 – 0.4 – µs Low Battery Trip Point 19 – 1.2 – Vdc Low Battery Output – VCC = 0.9 V Low Battery Output – VCC = 1.3 V 20 20 – – 0.2 VCC – – Vdc Regulated Output (see Figure 4) 17 0.95 1.07 1.15 Vdc Source Capability 17 – – 3.0 mA COMPARATOR LOW BATTERY DETECTOR Figure 1. MC3374 Pager IF Application Circuit RF Input 50 FL2 FL1 L1 0.01 CC1 C1 C2 CC2 180 k 0.1 CB CB 32 31 30 29 28 27 26 25 – L2 CC3 RD X 1 Mixer C3 2nd IF 2 C4 39 k 1st IF 23 Audio Buffer 1.0 µF 22 Voltage Reference 4 330 24 MC3374 3 CB Data Buffer 21 3900 P 0.1 5 Output Buffer 6 10 7 8 Low Battery Detector Low Pass Filter Main Current Reference Quadrature Demodulator 19 10 11 12 13 14 15 17 0.022 3.3 k 16 Disable N.C. N.C. 100 10 1.0 9 LC1 8.2 k 0.1 0.1 56 k 8.2 k 20 18 Receiver Voltage Enable Reference Comp. 100 k 0.22 RL Enable 4.7+ VCC VEE Data Output NOTES: 1. FL1 and FL2 are 455 kHz ceramic bandpass filters, which should have input and output impedances of 1.5 kΩ to 2.0 kΩ. Suggested part numbers are MuRata CFU455X or CFW455x – the ‘X’ suffix denotes bandwidth. 2. LC1 is a 455 kHz LC resonator. Recommended part numbers are Toko America RMC2A6597HM or 5SVLC–0637BGT (smaller). The evaluation board layout shown provides for use of either resonator. Ceramic discriminator elements cannot be used with the MC3374 due to their low input impedance. The damping resistor value can be raised to increase the recovered audio or lowered to increase the quadrature detector’s bandwidth and linearity – practical limits are approximately 27 kΩ to 75 kΩ. Typically the quadrature detector’s bandwidth should match the low IF filter’s bandwidth. 3. The data buffer is set up as a low–pass filter with a corner frequency of approximately 200 Hz. The audio buffer is a bandpass filter with corner frequencies of 300 Hz and 3.0 kHz. The audio amplifier provides bass suppression. Audio Output 4. CC1 and CC3 are RF coupling capacitors and should have ≤ 20 Ω impedance at the desired input and oscillator frequencies. 5. CC2 provides “light coupling” of the oscillator signal into the mixer, and should have a 3.0 kΩ to 5.0 kΩ impedance at the desired local oscillator frequency. 6. Capacitors labelled CB are bypass capacitors and should have 20 Ω impedance at the desired RF and local oscillator frequencies. 7. The network of L1, C1 and C2 provides impedance matching of the mixer input (nominally 3.0 kΩ shunted by 9.0 pF) to 50 Ω at the desired RF/IF input frequency. This will allow for bench testing of the receiver from typical RF signal generators or radio service monitors, but additional or different matching will be required to maximize receiver sensitivity when used in conjunction with an antenna, RF preamplifier or mixer. MOTOROLA ANALOG IC DEVICEFor DATA More Information On This Product, Go to: www.freescale.com 3 ARCHIVE INFORMATION Freescale Semiconductor, Inc... ARCHIVE INFORMATION VOLTAGE REGULATOR Freescale Semiconductor, Inc. MC3374 In. Freq. L1 L2 C1 C2 C3 C4 CC1/CC3 CC2 CB RD 10.7 MHz 6.8 µH Short 2 – 82 pF 10 pF 120 pF 50 pF 1.0 nF 5.0 pF 0.1 µF Open 45 MHz 0.68 µH 1.2 µH 5 – 25 pF Open 30 pF 5.0 pF 1.0 nF 1.0 pF 1.0 nF 1.0 k 72 MHz 0.22 µH 0.22 µH 5 – 25 pF Open 18 pF 3.0 pF 470 pF 1.0 pF 470 pF 1.0 k Figure 2. Recovered Audio versus Supply Figure 3. S+N, N versus Input 30 20 10 N, S+N (dB) 40 30 0 S+N – 10 – 20 V6 – 40 10 N – 60 – 120 – 110 – 100 – 90 0 0 1.0 2.0 3.0 4.0 – 80 VCC (V) V17, REGULATED OUTPUT (mVdc) 1000 800 600 RL = ∞ 400 RL = 990 200 RL = 330 0 0 1.0 2.0 – 60 – 50 – 40 – 30 Figure 5. Regulated Output and Recovered Audio versus Temperature Figure 4. VREG versus Supply 1200 – 70 INPUT (dBm) 3.0 4.0 5.0 1140 18.0 1120 17.5 V6 1100 17.0 1080 16.5 1060 16.0 V17 1040 15.5 1020 15.0 1000 – 50 – 25 0 25 50 75 100 14.5 125 TA, AMBIENT TEMPERATURE (°C) VCC (V) Figure 6. Buffer Amplifier Gains versus Temperature A vab , AUDIO BUFFER GAIN (V/V) 2.98 3.99 Avdb 2.93 3.97 Avab 3.95 2.88 3.93 2.83 3.91 – 50 – 25 0 25 50 75 100 A vdb , DATA BUFFER GAIN (V/V) 3.03 4.01 2.78 125 TA, AMBIENT TEMPERATURE (°C) 4 MOTOROLA ANALOG IC DEVICE DATA For More Information On This Product, Go to: www.freescale.com ARCHIVE INFORMATION – 30 20 V6, RECOVERED AUDIO (mVrms) RECOVERED AUDIO (mVrms) V22 50 – 50 V17, VOLTAGE REGULATION (mV) Freescale Semiconductor, Inc... ARCHIVE INFORMATION 60 Freescale Semiconductor, Inc. MC3374 Figure 7. MC3374 Pager Receiver PCB Artwork COPPER 1 LAYER (Actual View of Surface Mount Side) RF Input COPPER 2 LAYER (Caution: Reversed View of Through–Hole Side) VEE MC3374FTB VCC ARCHIVE INFORMATION Freescale Semiconductor, Inc... ARCHIVE INFORMATION 2.2″ Enable Data Output Disable 2.0″ COMPONENT 1 LAYER C2 FL1 1.0 3900 P X 0.1 L2 0.01 0.01 0.33 k 0.01 10 39 k 180 k 0.022 8.2 k LC1 0.1 CB 56 K VCC GND C3 C4 4.7 CB CB RD CC3 FL2 CC1 CC2 C1 RF I/P GND VCC L1 COMPONENT 2 LAYER 1.0 0.1 10 3.3 k LED 100 K 8.2 k 0.22 Data O/P RL Enable Disable SMA NOTE: + = Through Hole MOTOROLA ANALOG IC DEVICEFor DATA More Information On This Product, Go to: www.freescale.com 5 Freescale Semiconductor, Inc. MC3374 The MC3374 is an FM narrowband receiver capable of operation to 75 MHz. The low voltage design yields low power drain and excellent sensitivity in narrowband voice and data link applications. In the typical application the mixer amplifies the incoming RF or IF signal and converts this frequency to 455 kHz. The signal is then filtered by a 455 kHz ceramic filter and applied to the first intermediate frequency (IF) amplifier input, before passing through a second ceramic filter. The modulated IF signal is then applied to the limiting IF amplifier and detector circuitry. Modulation is recovered by a conventional quadrature detector. The typical modulation bandwidth available is 3.0 to 5.0 kHz. Features available include buffers for audio/data amplification and active filtering, on board voltage regulator, low battery detection circuitry with programmable level, and receiver disable circuitry. The MC3374 is an FM utility receiver to be used for voice and/or narrowband data reception. It is especially suitable where extremely low power consumption and high design flexibility are required. APPLICATION The MC3374 can be used as a high performance FM IF for the use in low power dual conversion receivers. Because of the MC3374’s extremely good sensitivity (0.6 µV for 20 dB (S+N/N, see Figure 3)), it can also be used as a stand alone single conversion narrowband receiver to 75 MHz for applications not sensitive to image frequency interference. An RF preamplifier will likely be needed to overcome preselector losses. The oscillator is a Colpitts type which must be run under crystal control. For fundamental mode crystals choose resonators, parallel resonant, for a 32 pF load. For higher frequencies, use a 3rd overtone series mode type. The coil L2 and RD resistor are needed to ensure proper operation. The best adjacent channel and sensitivity response occur when two 455 kHz ceramic filters are used, as shown in Figure 1. Either can be replaced by a 0.1 µF coupling capacitor to reduce cost, but some degradation in sensitivity and/or stability is suspected. The detector is a quadrature type, with the connection from the limiter output to the detector input provided internally. A 455 kHz LC tank circuit must be provided externally. One of the tank pins (Pin 8) must be decoupled using a 0.1 µF capacitor. The 56 kΩ damping resistor (see Figure 1), determines the peak separation of the detector (and thus its bandwidth). Smaller values will increase the separation and bandwidth but decrease recovered audio and sensitivity. The data buffer is a noninverting amplifier with a nominal voltage gain of 2.7 V/V. This buffer needs its dc bias (approximately 250 mV) provided externally or else debiasing will occur. A 2nd order Sallen–Key low pass filter, as shown in Figure 1, connecting the recovered audio output to the data buffer input provides the necessary dc bias and some post detection filtering. The buffer can also be used as an active filter. 6 The audio buffer is a noninverting amplifier with a nominal voltage gain of 4.0 V/V. This buffer is self–biasing so its input should be ac coupled. The two buffers, when applied as active filters, can be used together to allow simultaneous audio and very low speed data reception. Another possible configuration is to receive audio only and include a noise–triggered squelch. The comparator is a noninverting type with an open collector output. Typically, the pull–up resistor used between Pin 14 and VCC is 100 kΩ. With RL = 100 kΩ the comparator is capable of operation up to 25 kHz. The circuit is self–biasing, so its input should be ac coupled. The regulator is a 1.07 V reference capable of sourcing 3.0 mA. This pin (Pin 17) needs to be decoupled using a 1.0 – 10 µF capacitor to maintain stability of the MC3374. All three VCCs on the MC3374 (VCC, VCC2, VCC3) run on the same supply voltage. VCC is typically decoupled using capacitors only. VCC2 and VCC3 should be bypassed using the RC bypasses shown in Figure 1. Eliminating the resistors on the VCC2 and VCC3 bypasses may be possible in some applications, but a reduction in sensitivity and quieting will likely occur. The low battery detection circuit gives an NPN open collector output at Pin 20 which drops low when the MC3374 supply voltage drops below 1.2 V. Typically it would be pulled up via a 100 kΩ resistor to supply. The 1.2 V Select pin, when connected to the MC3374 supply, programs the low battery detector to trip at VCC < 1.1 V. Leaving this pin open raises the trip voltage on the low battery detector. Pin 15 is a receiver enable which is connected to VCC for normal operation. Connecting this pin to ground shuts off receiver and reduces current drain to ICC < 0.5 µA. APPENDIX Design of 2nd Order Sallen–Key Low Pass Filters C1 R1 Input R2 Low Pass Output 0 to fo Hz + – C2 Bias Avo = K ARCHIVE INFORMATION Freescale Semiconductor, Inc... ARCHIVE INFORMATION CIRCUIT DESCRIPTION The audio and data buffers can easily be configured as active low pass filters using the circuit configuration shown above. The circuit has a center frequency (fo) and quality factor (Q) given by the following: fo Q + 1 + 2p ǸR1R2C1C2 Ǹ )Ǹ R2C2 R1C1 1 R1C2 R2C1 ) (1–K) Ǹ R1C1 R2C2 If possible, let R1 = R2 or C1 = C2 to simplify the above equations. Be sure to avoid a negative Q value to prevent instability. Setting Q filter response. + 1 ńǸ2 + 0.707 yields a maximally flat MOTOROLA ANALOG IC DEVICE DATA For More Information On This Product, Go to: www.freescale.com Freescale Semiconductor, Inc. MC3374 Data Buffer Design Audio Buffer Design The data buffer is designed as follows: The audio buffer is designed as follows: fo = 200 Hz C1 = C2 = 0.01 µF Q = 0.707 (target) fo = 3000 Hz R1 = R2 = 8.2 kΩ Q = 0.707 (target) K = 3.9 (audio buffer open loop voltage gain) K = 2.7 (data buffer open loop voltage gain) Setting C1 = C2 yields: fo Freescale Semiconductor, Inc... ARCHIVE INFORMATION Q + + 2pC1 1ǸR1R2 Ǹ R2 R1 1 ) (2–K) fo Ǹ Q R1 R2 Iteration yields R2 = 4.2 (R1) to make Q = 0.707. Substitution into the equation for fo yields: R1 = 38 kΩ (use 39 kΩ) R2 = 4.2(R1) = 180 kΩ C1 = C2 = 0.01 µF + + 2pR1 1ǸC1C2 Ǹ C2 C1 1 ) (1–K) Ǹ C1 C2 ARCHIVE INFORMATION Setting C1 = C2 yields: Iteration yields C2 = 2.65 (C1) to make Q = 0.707. Substitution into the equation for fo yields: C1 = 3900 pF C2 = 2.65(C1) = 0.01 µF R1 = R2 = 8.2 kΩ Motorola reserves the right to make changes without further notice to any products herein. Motorola makes no warranty, representation or guarantee regarding the suitability of its products for any particular purpose, nor does Motorola assume any liability arising out of the application or use of any product or circuit, and specifically disclaims any and all liability, including without limitation consequential or incidental damages. “Typical” parameters which may be provided in Motorola data sheets and/or specifications can and do vary in different applications and actual performance may vary over time. All operating parameters, including “Typicals” must be validated for each customer application by customer’s technical experts. Motorola does not convey any license under its patent rights nor the rights of others. Motorola products are not designed, intended, or authorized for use as components in systems intended for surgical implant into the body, or other applications intended to support or sustain life, or for any other application in which the failure of the Motorola product could create a situation where personal injury or death may occur. Should Buyer purchase or use Motorola products for any such unintended or unauthorized application, Buyer shall indemnify and hold Motorola and its officers, employees, subsidiaries, affiliates, and distributors harmless against all claims, costs, damages, and expenses, and reasonable attorney fees arising out of, directly or indirectly, any claim of personal injury or death associated with such unintended or unauthorized use, even if such claim alleges that Motorola was negligent regarding the design or manufacture of the part. Motorola and are registered trademarks of Motorola, Inc. Motorola, Inc. is an Equal Opportunity/Affirmative Action Employer. MOTOROLA ANALOG IC DEVICEFor DATA More Information On This Product, Go to: www.freescale.com 7 Freescale Semiconductor, Inc. MC3374 OUTLINE DIMENSIONS FTB SUFFIX PLASTIC PACKAGE CASE 873–01 (Thin QFP) ISSUE A L 24 17 SD B P B 9 1 8 -A-,-B-,-DDETAIL A -DA 0.20 (0.008) M C A–B 0.05 (0.002) A–B S D S S D S F BASE METAL S 0.20 (0.008) M H A–B J DETAIL C M N D C E -H- -CSEATING PLANE H M G U T R -HDATUM PLANE K Q X DETAIL C How to reach us: USA / EUROPE / Locations Not Listed: Motorola Literature Distribution; P.O. Box 20912; Phoenix, Arizona 85036. 1–800–441–2447 or 602–303–5454 DATUM PLANE 0.20 (0.008) 0.01 (0.004) M C A–B S D S SECTION B-B VIEW ROTATED 90° CLOCKWISE NOTES: 1. DIMENSIONING AND TOLERANCING PER ANSI Y14.5M, 1982. 2. CONTROLLING DIMENSION: MILLIMETER. 3. DATUM PLANE -H- IS LOCATED AT BOTTOM OF LEAD AND IS COINCIDENT WITH THE LEAD WHERE THE LEAD EXITS THE PLASTIC BODY AT THE BOTTOM OF THE PARTING LINE. 4. DATUMS -A-, -B- AND -D- TO BE DETERMINED AT DATUM PLANE -H-. 5. DIMENSIONS S AND V TO BE DETERMINED AT SEATING PLANE -C-. 6. DIMENSIONS A AND B DO NOT INCLUDE MOLD PROTRUSION. ALLOWABLE PROTRUSION IS 0.25 (0.010) PER SIDE. DIMENSIONS A AND B DO INCLUDE MOLD MISMATCH AND ARE DETERMINED AT DATUM PLANE -H-. 7. DIMENSION D DOES NOT INCLUDE DAMBAR PROTRUSION. ALLOWABLE DAMBAR PROTRUSION SHALL BE 0.08 (0.003) TOTAL IN EXCESS OF THE D DIMENSION AT MAXIMUM MATERIAL CONDITION. DAMBAR CANNOT BE LOCATED ON THE LOWER RADIUS OR THE FOOT. DIM A B C D E F G H J K L M N P Q R S T U V X MILLIMETERS MIN MAX 7.10 6.95 7.10 6.95 1.60 1.40 0.273 0.373 1.50 1.30 — 0.273 0.80 BSC 0.20 — 0.119 0.197 0.57 0.33 5.6 REF 8° 6° 0.119 0.135 0.40 BSC 5° 10° 0.15 0.25 8.85 9.15 0.15 0.25 5° 11° 8.85 9.15 1.0 REF INCHES MIN MAX 0.274 0.280 0.274 0.280 0.055 0.063 0.010 0.015 0.051 0.059 — 0.010 0.031 BSC 0.008 — 0.005 0.008 0.013 0.022 0.220 REF 8° 6° 0.005 0.005 0.016 BSC 5° 10° 0.006 0.010 0.348 0.360 0.006 0.010 5° 11° 0.348 0.360 0.039 REF JAPAN: Nippon Motorola Ltd.; Tatsumi–SPD–JLDC, 6F Seibu–Butsuryu–Center, 3–14–2 Tatsumi Koto–Ku, Tokyo 135, Japan. 03–81–3521–8315 ASIA/PACIFIC: Motorola Semiconductors H.K. Ltd.; 8B Tai Ping Industrial Park, 51 Ting Kok Road, Tai Po, N.T., Hong Kong. 852–26629298 8 ◊ *MC3374/D* MOTOROLA ANALOG IC DEVICE DATA MC3374/D For More Information On This Product, Go to: www.freescale.com ARCHIVE INFORMATION DETAIL A 32 V H A–B B M ARCHIVE INFORMATION Freescale Semiconductor, Inc... L 0.20 (0.008) -B- -A- 0.20 (0.008) M C A–B 0.05 (0.002) A–B SD S 16 S 25