Microphone Preamplifier with a Variable Compression and Noise Gating SSM2165 FEATURES FUNCTIONAL BLOCK DIAGRAM Complete Microphone Conditioner in an 8-Lead Package Single +5 V Operation C2 10␮F Preset Noise Gate Threshold V+ + Compression Ratio Set by External Resistor Automatic Limiting Feature Prevents ADC Overload V+ BUFOUT VCAIN C1 RA RA 0.1␮F Adjustable Release Time AUDIO 2 2 +1 V IN+ VCA OUT Low Noise and Distortion BUFFER (kHz Bandwidth (؎1 dB 20 LEVEL Low Cost DETECTOR CONTROL APPLICATIONS SSM2165 Microphone Preamplifier/Processor AVG CAP Computer Sound Cards C3 + R1 COMPRESSION Public Address/Paging Systems GND 22␮F 25k⍀ RATIO SET OBSOLETECommunication Headsets Telephone Conferencing Guitar Sustain Effects Generator a VCA gain of 8 dB and gives –9.8 dBu (250 mV) before limiting. µ Computerized Voice Recognition Both have a noise gate threshold of –64 dBu (500 V), below Surveillance Systems which downward expansion reduces the gain with a ratio of Karaoke and DJ Mixers approximately 1:3. That is, a –3 dB reduction of output signal occurs with a –1 dB reduction of input signal. For applications GENERAL DESCRIPTION requiring adjustable noise gate threshold, VCA gain up to 18 dB, The SSM2165 is a complete and flexible solution for condition- and adjustable rotation point, please refer to the SSM2166. ing microphone inputs in computer audio systems. It is also 0 excellent for improving vocal clarity in communications and public address systems. A low noise voltage controlled amplifier –10 (VCA) provides a gain that is dynamically adjusted by a control –20 loop to maintain a set compression characteristic. The compres- sion ratio is set by a single resistor and can be varied from 1:1 to –30 over 15:1 relative to the fixed rotation point. Signals above the rotation point are limited to prevent overload and to eliminate OUTPUT – dBu –40 “popping.” A downward expander (noise gate) prevents amplifi- cation of noise or hum. This results in optimized signal levels –50 prior to digitization, thereby eliminating the need for additional –60 gain or attenuation in the digital domain that could add noise or –80 –70 –60 –50 –40 –30 –20 –10 INPUT – dBu impair accuracy of speech recognition algorithms. The flexibility of setting the compression ratio and the time constant of the Figure 1a. SSM2165-1 Compression and Gating Characteristics level detector, coupled with two values of rotation point, make 0 the SSM2165 easy to integrate in a wide variety of microphone –10 conditioning applications. –20 The SSM2165 is an ideal companion product for audio codecs used in computer systems, such as the AD1845 and AD1847. –30 The device is available in 8-lead SOIC and P-DIP packages, and –40 guaranteed for operation over the extended industrial temperature OUTPUT – dBu range of –40°C to +85°C. As shown in Figure 1a, the SSM2165-1 –50 1 has a rotation point of –25.7 dBu (40 mV) , a VCA gain of 18 dB, –60 and gives –7.7 dBu (320 mV) before limiting. As shown in Figure –70 1b, the SSM2165-2 has a rotation point of –17.8 dBu (100 mV), –80 –70 –60 –50 –40 –30 –20 –10 INPUT – dBu 1All signals are in rms volts or dBu (0 dBu = 0.775 V rms). Figure 1b. SSM2165-2 Compression and Gating Characteristics REV. A Information furnished by Analog Devices is believed to be accurate and reliable. However, no responsibility is assumed by Analog Devices for its use, nor for any infringements of patents or other rights of third parties One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A. which may result from its use. No license is granted by implication or Tel: 781/329-4700 World Wide Web Site: http://www.analog.com otherwise under any patent or patent rights of Analog Devices. Fax: 781/326-8703 © Analog Devices, Inc., 1999 ⍀ ⍀ ؇ SSM2165–SPECIFICATIONS (V+ = +5 V, f = 1 kHz, RL = 100 k , RCOMP = 0 , TA = +25 C, unless otherwise noted) Parameter Symbol Conditions Min Typ Max Units AUDIO SIGNAL PATH 2 Voltage Noise Density en 15:1 Compression, VIN = GND 17 nV/√Hz 1 Noise 20 kHz Bandwidth, VIN = GND –109 dBu Total Harmonic Distortion THD+N SSM2165-1 2nd and 3rd Harmonics, VIN = –30 dBu 0.2 0.5 % SSM2165-2 2nd and 3rd Harmonics, VIN = –20 dBu 0.2 0.5 % 22 kHz Low-Pass Filter Input Impedance ZIN 180 kΩ Output Impedance ZOUT 75 Ω Load Drive Resistive 5 kΩ Capacitive 2 nF Input Voltage Range 1% THD 1 V rms Output Voltage Range 1% THD 1.4 V rms Gain Bandwidth Product 1:1 Compression SSM2165-1 VCA G = 18 dB 300 kHz SSM2165-2 VCA G = 8 dB 100 kHz CONTROL SECTION VCA Dynamic Gain Range 40 dB VCA Fixed Gain OBSOLETESSM2165-1 18 dB SSM2165-2 8dB Rotation Point SSM2165-1 40 mV rms SSM2165-2 100 mV rms Compression Ratio, Min 1:1 Compression Ratio, Max 15:1 Control Feedthrough 15:1 Compression ±5mV POWER SUPPLY Supply Voltage Range VS 4.5 5.5 V Supply Current ISY 7.5 10 mA Quiescent Output Voltage Level 2.2 V Power Supply Rejection Ratio2 PSRR 50 dB NOTES 10 dBu = 0.775 V rms. 2Referred to input. Specifications subject to change without notice. –2– REV. A SSM2165 ABSOLUTE MAXIMUM RATINGS PIN CONFIGURATION Supply Voltage . +10 V Audio Input Voltage . .Supply Voltage ° ° Operating Temperature Range . –40 C to +85 C GND 1 8 V+ Storage Temperature Range . –65°C to +150°C SSM2165 VCAIN 2 7 OUTPUT Junction Temperature (TJ) . .+150°C TOP VIEW BUFOUT 3 6 COMP RATIO SET Lead Temperature (Soldering, 60 sec) . .+300°C (Not to Scale) AUDIO +IN 4 5 AVG CAP ESD RATINGS 883 (Human Body) Model . 2.0 kV THERMAL CHARACTERISTICS Thermal Resistance PIN FUNCTION DESCRIPTIONS 8-Lead Plastic DIP θ ° JA . 103 C/W Pin # Mnemonic Function θJC . 43°C/W 8-Lead SOIC 1 GND Ground θJA . 158°C/W 2 VCAIN VCA Input Pin. A typical µ µ θJC . 43°C/W connection is a 1 F–10 F capacitor from the buffer output pin (Pin 3) to this pin. 3 BUFOUT Input Buffer Amplifier Output OBSOLETEORDERING GUIDE Pin. Must not be loaded by capacitance to ground. Temperature Package Package 4 AUDIO +IN Input Audio Signal. The input Model Range Description Options signal should be ac-coupled SSM2165-1P –40°C to +85°C Plastic DIP N-8 (0.1 µF typical) into this pin. SSM2165-2P –40°C to +85°C Plastic DIP N-8 5 AVG CAP Detector Averaging Capacitor. SSM2165-1S –40°C to +85°C Narrow SOIC SO-8 A capacitor, 2.2 µF–22 µF, to SSM2165-2S –40°C to +85°C Narrow SOIC SO-8 ground from this pin is the averaging capacitor for the detector circuit. 6 COMP RATIO SET Compression Ratio Set Pin. A resistor to ground from this pin sets the compression ratio as shown in Figure 1. 7 OUTPUT Output Signal. 8 V+ Positive Supply, +5 V Nominal. CAUTION ESD (electrostatic discharge) sensitive device. Electrostatic charges as high as 4000 V readily accumulate on the human body and test equipment and can discharge without detection. WARNING! Although the SSM2165 features proprietary ESD protection circuitry, permanent damage may occur on devices subjected to high energy electrostatic discharges. Therefore, proper ESD precautions are recommended to avoid performance degradation or loss of functionality. ESD SENSITIVE DEVICE REV. A –3– SSM2165–Typical Performance Characteristics 260 ؇ 240 TA = +25 C VS = +5V 220 ⍀ RL = 100k 5␮V 200 1s 180 100 90 160 ⍀ 140 – k 120 COMP R 100 SSM2165–1 ؇ 80 10 TA = +25 C 60 0% COMPRESSION RATIO = 15:1 SSM2165–2 NOISE BW = 20kHz 40 20 0 1:12:1 5:1 10:1 15:1 COMPRESSION RATIO Figure 2. Compression Ratio vs. RCOMP Figure 5. Wideband Output Noise 5 70 T = +25؇C A COMP RATIO = 15:1 OBSOLETECOMP RATIO = 1:1 60 R = 0 R = 100k⍀/10k⍀ COMP L ␮ VIN = 40 V rms VS = +5V 50 40 1 30 G = 18dB 20 THD+N – % GAIN – dB SSM2165–1 10 G = 8dB 0 SSM2165–2 0.1 –10 0.050 –20 0.010.1 1 1k10k 100k 1M INPUT – V rms FREQUENCY – Hz Figure 3. THD + N (%) vs. Input (V rms) Figure 6. GBW Curves vs. VCA Gain –30 ؇ 5 TA = +25 C VS = +5V COMP RATIO = 1:1 VIN = –20dBu (–1) VIN = –30dBu (–2) –40 ⍀ RL = 100k 1 ؎ –50 V+ = 5 1V p-p THD+N – % PSRR – dB SSM2165–1 –60 0.1 SSM2165–2 0.050 –70 20100 1k 10k 30k 20100 1k 10k 30k FREQUENCY – Hz FREQUENCY – Hz Figure 4. THD + N (%) vs. Frequency (Hz) Figure 7. PSRR vs. Frequency, Referred to Input –4– REV. A SSM2165 20mV 200mV 100 100 90 90 T = +25؇C ؇ A TA = +25 C C = 2.2␮F ␮ AVG CAVG = 2.2 F R = 10k⍀ ⍀ L RL = 10k COMP RATIO = 1:1 10 10 COMP RATIO = 1:1 V = 12.5mV (–1) 0% IN 0% VIN = 125mV (–1) V = 40mV (–2) IN VIN = 400mV (–2) 10␮s 10␮s Figure 8. Small Signal Transient Response Figure 9. Large Signal Transient Response APPLICATIONS INFORMATION THEORY OF OPERATION The SSM2165 is a complete microphone signal conditioning Figure 10 illustrates the general transfer characteristic for the system in a single integrated circuit. Designed primarily for SSM2165 where the output level in dBu is plotted as a function voiceband applications, this integrated circuit provides amplifi- of the input level in dBu (0 dBu = 0.775 V rms). For input cation, rms detection, limiting, variable compression, and down- signals in the range of VDE (Downward Expansion) to VRP ward expansion.