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a ssm2167 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 that may result from its use. no license is granted by implication or otherwise under any patent or patent rights of analog devices. trademarks and registered trademarks are the property of their respective owners. one technology way, p.o. box 9106, norwood, ma 02062-9106, u.s.a. tel: 781/329-4700 www.analog.com fax: 781/326-8703 ? 2003 analog devices, inc. all rights reserved. rev. b low voltage microphone preamplifier with variable compression and noise gating features complete microphone conditioner in a 10-lead package single 3 v operation low shutdown current < 2 a adjustable noise gate threshold adjustable compression ratio automatic limiting feature prevents adc overload low noise and distortion: 0.2% thd + n 20 khz bandwidth applications desktop, portable, or palmtop computers telephone conferencing communication headsets two-way communications surveillance systems karaoke and dj mixers general description the ssm2167 is a complete and flexible solution for conditioning microphone inputs in personal electronics and computer audio systems. it is also excellent for improving vocal clarity in communi- cations and public address systems. a low noise voltage controlled amplifier (vca) provides a gain that is dynamically adjusted by a control loop to maintain a set compression characteristic. the compression ratio is set by a single resistor and can be varied from 1:1 to over 10:1 relative to the fixed rotation point. signals above the rotation point are limited to prevent overload and to eliminate popping. a downward expander (noise gate) prevents amplification of background noise or hum. this results in optimized signal levels prior to digitization, thereby eliminating the need for additional gain or attenuation in the digital domain. the flexibility of setting the compression ratio and the time constant of the level detector, coupled with two values of rotation point, make the ssm2167 easy to integrate in a wide variety of microphone conditioning applications. the device is available in a 10-lead msop package, and is guaran- teed for operation over the extended industrial temperature range of ?0 c to +85 c. pin configuration 10-lead msop (rm suffix) input ?db output ?db limiting region limiting threshold (rotation point) compression region 1 r 1 1 downward expansion threshold (noise gate) downward expansion region v de v rp vca gain figure 1. general input/output characteristics ssm2167 gnd vca in shutdown buf out input v dd output compression ratio gate thrs avg cap 1 2 3 4 5 10 9 8 7 6
rev. b e2e ssm2167especifications (@ v s = 3.0 v, f = 1 khz, r l = 100 k , r comp = 0 , t a = 25 c, v in = 100 mv rms, r gate = 2 k , unless otherwise noted.) parameter symbol conditions min typ max unit audio signal path voltage noise density e n 10:1 compression 20 nv / hz hz h h h h hz h a specifications subject to change without notice.
rev. b e3e ssm2167 absolute maximum ratings * supply voltage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 v input voltage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 v operating temperature range . . . . . . . . . . . e40 c to +85 c junction temperature range . . . . . . . . . . . . . . . . . . . . 150 c lead temperature range (soldering, 10 sec) . . . . . . . 300 c esd ratings 883 (human body) model . . . . . . . . . . . . . . . . . . . . . . 500 v * stresses above those listed under absolute maximum ratings may cause perma- nent damage to the device. this is a stress rating only; functional operation of the device at these or any other conditions above those listed in the operational sections of this specification is not implied. exposure to absolute maximum rating condi- tions for extended periods may affect device reliability. package type ja * jc unit 10-lead msop (rm) 180 35 c/w * ja is specified for worst-case conditions, i.e., ja is specified for device soldered in 4-layer circuit board for surface-mount packages. 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. although the ssm2167 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. warning! esd sensitive device ordering guide temperature package model range package description option ssm2167-1rm-reel e40 c to +85 c 10-lead mini/micro soic (msop) rm-10 ssm2167-1rm-r2 e40 c to +85 c 10-lead mini/micro soic (msop) rm-10 SSM2167-EVAL evaluation board
rev. b ssm2167 e4e e typical performance characteristics r gate e 100 10 1 03, 500 500 noise gate e mv rms 1,000 1,500 2,500 2,000 3,000 t a = 25 c v+ = 3v r load = 100k compression ratio 2:1 ro ta tion point = 63mv rms tpc 1. noise gate vs. r gate frequency e hz 20 30k thd + n e % 100 1k 10k 1 0.01 0.1 20k t a = 25 c v+ = 3v v in = 24.5mv rms compression ratio 1:1 rotation point = 63mv rms noise gate setting = 1.4mv rms tpc 2. thd + n vs. frequency frequency e hz 1k 10m 10k gain e db 100k 1m 35 15 5 15 5 25 v in = 2mv rms r comp = 175k rotation point = 63mv rms noise gate setting = 1.4mv rms tpc 3. gbw curves vs. vca gain input voltage e v rms 1 0.1 0.01 10m 1 0.1 thd + n e % t a = 25 c v+ = 3v v in frequency = 1khz r load = 100k compression ratio 1:1 ro ta tion point = 63mv rms noise gate setting = 1.4mv rms tpc 4. thd + n vs. input input e dbv 0 80 80 70 output e dbv 60 50 40 30 20 10 10 40 50 60 70 20 30 t a = 25 c v+ = 3v r l = 100k ro ta tion point = 63mv rms noise gate setting = 1.4mv rms compression ratio 1:1 compression ratio 5:1 compression ratio 10:1 compression ratio 2:1 tpc 5. output vs. input characteristics frequency e hz 10 20 80 10 100k 100 psrr e db 1k 10k 30 40 50 60 70 v+ = 3v + 0.1 r gate = 5k r comp = 0v tpc 6. psrr vs. frequency
rev. b e5e ssm2167 time e 10 s/div 0 0 00 0 vo lta ge e 50mv/div 000000 0 0 0 0 0 0 0 t a = 25 c c sys = 10 f system gain = 19db r load = 100k compression ratio 1:1 tpc 7. small signal transient response time e 10 s/div 0 0 00 0 vo lta ge e 500mv/div 000000 0 0 0 0 0 0 0 t a = 25 c c sys = 10 f system gain = 8.6db r load = 100k compression ratio 1:1 tpc 8. large signal transient response time e 10 s/div 0 0 00 0 vo lta ge e 50mv/div 000000 0 0 0 0 0 0 0 t a = 25 c c sys = 10 f system gain = 8db r load = 100k compression ratio 1:1 tpc 9. small signal transient response time e 10 s/div 0 0 00 0 vo lta ge e 200mv/div 000000 0 0 0 0 0 0 0 t a = 25 c c sys = 10 f system gain = 2.6db r load = 100k compression ratio 1:1 tpc 10. large signal transient response time e 1s/div 0 0 00 0 vo lta ge e 100mv/div 000000 0 0 0 0 0 0 0 85dbv 66dbv 6dbv tpc 11. rms level detector performance with c avg = 22 f time e 500ms/div 0 0 00 0 vo lta ge e 100mv/div 000000 0 0 0 0 0 0 0 85dbv 66dbv 6dbv tpc 12. rms level detector performance with c avg = 2.2 f
rev. b ssm2167 e6e applications information the ssm2167 is a complete microphone signal conditioning system on a single integrated circuit. designed primarily for voice band applications, this integrated circuit provides amplifi- cation, limiting, variable compression, and noise gate. user adjustable compression ratio, noise gate threshold, and two different fixed gains optimize circuit operation for a variety of applications. the ssm2167 also features a low power shutdown mode for battery-powered applications. 10 f v dd gnd shutdown v dd r gate r comp output 0.1 f input 10 f + 10 f + 100k gnd v dd 10 f + 500k ssm2167 figure 2. typical application circuit level detector control r g r c c3 10 f + c avg noise gate and compression settings gnd shutdown vca +1 input c1 0.1 f buffer c2 10 f buf out output v dd vca in + 1k 1k v dd figure 3. functional block diagram theory of operation the typical transfer characteristic for the ssm2167 is shown in figure 1 where the output level in db is plotted as a function of the input level in db. the dotted line indicates the transfer characteristic for a unity-gain amplifier. for input signals in the range of v de (downward expansion) to v rp (rotation point) an r db change in the input level causes a 1 db change in the output level. here, r is defined as the compression ratio. the compression ratio may be varied from 1:1 (no compression) to 10:1 via a single resistor, r comp . input signals above v rp are compressed with a fixed compression ratio of approximately 10:1. this region of operation is the limiting region. varying the compression ratio has no effect on the limiting region. the breakpoint between the compression region and the limiting region is referred to as the limiting threshold or the rotation point. the term rotation point derives from the observation that the straight line in the compression region rotates about this point on the input/output characteristic as the compression ratio is changed. the gain of the system with an input signal level of v rp is the fixed gain, 18 dbv for the ssm2167-1, regardless of the com- pression ratio. input signals below v de are downward-expanded; that is, a e1 db change in the input signal level causes approximately a e3 db change in the output level. as a result, the gain of the system is small for very small input signal levels, even though it may be quite large for small input signals just above of v de . the external resistor at pin 7, r gate , is used to set the downward expansion threshold v de . finally, the ssm2167 provides an active low, cmos compatible digital power-down feature that will reduce device supply current to typically less than 2 a. ssm2167 signal path figure 3 illustrates the block diagram of the ssm2167. the audio input signal is processed by the input buffer and then by the vca. the input buffer presents an input impedance of approximately 100 k to the source. a dc voltage of approximately 1.5 v is present at input (pin 5 of the ssm2167), requiring the use of a blocking capacitor (c1) for ground-referenced sources. a 0.1 f capacitor is a good choice for most audio applications. the input buffer is a unity-gain stable amplifier that can drive the low imped- ance input of the vca and an internal rms detector. the vca is a low distortion, variable-gain amplifier whose gain is set by the side-chain control circuitry. an external blocking capacitor (c2) must be used between the buffer?s output and the vca input. the 1 k impedance between amplifiers determines the value of this capacitor, which is typically between 4.7 f and 10 f. an aluminum electrolytic capacitor is an economical choice. the vca amplifies the input signal current flowing through c2 and converts this current to a voltage at the ssm2167?s output pin (pin 9). the net gain from input to output can be as high as 40 db, depending on the gain set by the control circuitry. the output impedance of the ssm2167 is typically less than 145 , and the external load on pin 9 should be > 5 k . the nominal output dc voltage of the device is approximately 1.4 v, so a blocking capacitor for grounded loads must be used. time e 500ms/div 0 0 00 0 vo lta ge e 100mv/div 000000 0 0 0 0 0 0 0 85dbv 66dbv 6dbv tpc 13. rms level detector performance with c avg = 2.2 f
rev. b e7e ssm2167 the bandwidth of the ssm2167 is quite wide at all gain settings. the upper 3 db point is over 1 mhz at gains as high as 30 db. the gbw plots are shown in tpc 3. the lower 3 db cutoff frequency of the ssm2167 is set by the input impedance of the vca (1 k ) and c2. while the noise of the input buffer is fixed, the input-referred noise of the vca is a function of gain. the vca input noise is designed to be a minimum when the gain is at a maximum, thereby maximizing the usable dynamic range of the part. level detector the ssm2167 incorporates a full-wave rectifier and a patent- pending, true rms level detector circuit whose averaging time constant is set by an external capacitor (c avg ) connected to the avg cap pin (pin 8). for optimal low frequency operation of the level detector down to 10 hz, the value of the capacitor should be 2.2 f. some experimentation with larger values for c avg may be necessary to reduce the effects of excessive low frequency ambient background noise. the value of the aver- aging capacitor affects sound quality: too small a value for this capacitor may cause a pumping effect for some signals, while too large a value can result in slow response times to signal dynamics. electrolytic capacitors are recommended here for lowest cost and should be in the range of 2 f to 22 f. the rms detector filter time constant is approximately given by 10 c avg milliseconds where c avg is in f. this time constant controls both the steady state averaging in the rms detector as well as the release time for compression; that is, the time it takes for the system gain to increase due to a decrease in input signal. the attack time, the time it takes for the gain to be reduced because of a sudden increase in input level, is controlled mainly by internal circuitry that speeds up the attack for large level changes. this limits overload time to less than 1 ms in most cases. the performance of the rms level detector is illustrated in tpc 12 for a c avg of 2.2 f and tpc 11 for a c avg of 22 f. in each of these photographs, the input signal to the ssm2167 (not shown) is a series of tone bursts in six successive 10 db steps. the tone bursts range from e66 dbv (0.5 mv rms) to e6 dbv (0.5 v rms). as illustrated in the photographs, the attack time of the rms level detector is dependent only on c avg , but the release times are linear ramps whose decay tim es are dependent on both c avg and the input signal step size. the rate of release is approximately 240 db/s for a c avg of 2.2 f, and 12 db/s for a c avg of 22 f. control circuitry the output of the rms level detector is a signal proportional to the log of the true rms value of the buffer output with an added dc offset. the control circuitry subtracts a dc voltage from this signal, scales it, and sends the result to the vca to control the gain. the vca?s gain control is logarithmic?a linear change in control signal causes a db change in gain. it is this control law that allows linear processing of the log rms signal to provide the flat compression characteristic on the input/output characteristic shown in figure 1. input e db output e db v de v rp 15:1 5:1 2:1 1:1 1 1 vca gain figure 4. effect of varying the compression ratio setting the compression ratio changing the scaling of the control signal fed to the vca causes a change in the circuit?s compression ratio, r. this effect is shown in figure 4. connecting a resistor (r comp ) between pin 8 and v dd sets the compression ratio. lowering r comp gives smaller compres- sion ratios as indicated in table i. agc performance is achieved with compression ratios between 2:1 and 10:1, and is dependent on the application. shorting r comp will disable the agc function, setting the compression equal to 1:1. if using a compression resis- tor, using a value greater than 5 k is recommended. if lower than 5 k is used, the device may interpret this as a short, 0 . table i. setting compression ratio compression ratio value of r comp 1:1 0 (short to v+) 2:1 15 k 3:1 35 k 5:1 75 k 10:1 175 k vca gain input e db output e db v de1 v rp v de3 v de2 1 1 r:1 figure 5. effects of varying the downward expansion (noise gate) threshold
rev. b ssm2167 e8e setting the noise gate threshold (downward expansion) noise gate threshold is another programmable point using an external resistor (r gate ) that is connected between pin 7 (noise gate thrs) and v dd . the downward expansion threshold may be set between e40 dbv and e55 dbv, as shown in table ii. the downward expansion threshold is inversely proportional to the value of this resistance: setting this resistance to 0 sets the threshold at approximately 10 mv rms (e40 dbv), whereas a 5 k resistance sets the threshold at approximately 1 mv rms (e55 dbv). this relationship is illustrated in figure 5. we do not recommend more than 5 k for the r gate resistor as the noise floor of the ssm2167 prevents the noise gate from being lowered further without causing problems. table ii. setting noise gate threshold noise gate (dbv) value of r gate e40 0 (short to v+) e48 1 k e54 2 k e55 5 k rotation point (limiting) input signals above a particular level, the rotation point, are attenuated (limited) by internal circuitry. this feature allows the ssm2167 to limit the maximum output, preventing clipping of the following stage, such as a codec or adc. the rotation point for ssm2167 is set internally to e24 dbv (63 mv rms). shutdown feature the supply current of the ssm2167 can be reduced to under 10 a by applying an active low, 0 v cmos compatible input to the ssm2167?s shutdown ss o sstss ss ss ss tss sss t t ssd ss
rev. b ? ssm2167 outline dimensions 10-lead mini small outline package [msop] (rm-10) dimensions shown in millimeters 0.23 0.08 0.80 0.60 0.40 8 0 0.15 0.00 0.27 0.17 0.95 0.85 0.75 seating plane 1.10 max 10 6 5 1 0.50 bsc 3.00 bsc 3.00 bsc 4.90 bsc pin 1 coplanarity 0.10 compliant to jedec standards mo-187ba
rev. b ssm2167 e10e revision history location page 9/03 data sheet changed from rev. a to rev. b. deleted ssm2167-2 model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . universal updated ordering guide . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 edits to figures 2 and 3 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 updated outline dimensions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 3/02 data sheet changed from rev. 0 to rev. a. edits to specifications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 edits to figures 2 and 3 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
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