SSM2015P ,+-18V; low noise microphone preamplifierGENERAL DESCRIPTION
The SSM-2015 is an ultra-low noise audio preamplifier particu-
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SSM2015P
+-18V; low noise microphone preamplifier
ANALOG
DEVICES
Low Noise Microphone
Preamplifier
SSM-ZDI 5
FEATURES
. Ultra Low Voltage Noise ................................... 1.3nV/x/E
. Wide Bandwidth .................................... 700kHz @ G = 100
. High Slew Rate ........................................................... 8V/ps
. Very Low Harmonic Distortion ....-.. 0.007% tii) G = 100
. Excellent CMR ........................................................... 100dB
. True Differential "Instrumentation" Type Inputs
. Programmable Input Stage Optimizes e" vs Rm
. Low Cost
ORDERING INFORMATION
OPERATING TEMPERATURE
SSM-2015P -ItrC to +55°C
Storage Temperature -55''C to ol25T
GENERAL DESCRIPTION
The SSM-2015 is an ultra-low noise audio preamplifier particu-
larly suited to microphone preamplification. Gains from 10 to over
2000 can be selected with wide bandwidth and low distortion over
the full gain range.
The very low voltage noise performance (1 .3nVA/Hz) of the SSM-
2015 is enhanced by a programmable input stage which allows
overall noise to be optimized for source impedances of upto 4KO.
The SSM-2015'strue differential inputs with high common-mode
rejection provide easy interfacing to flotation transducers such
as balanced microphone outputs, as well as single ended
devices.
BLOCK DIAGRAM
The SSM-2015 also offers high slew rate of about 8V/ps and full
DC coupling without any crossover distortion.
This device is packaged in a 14-pin epoxy DIP and is guaran-
teed over the operating temperature range of --10oC to +5590.
PIN CONNECTION
comm , . V E ans
N.C. 2 El 'NULL
'T, ff g”: 14-PIN EPOXY DIP
" E E -Rs (P-Suffix)
COMP 2 LE E] MN
com a [E El -NULL
ABSOLUTE MAXIMUM RATINGS
Supply Voltage ................................................................. t18V
Operating Temperature Range ....................... -1ty'C to +55°C
Junction Temperature .................................................... +150C
Storage Temperature .................................... --55oC to +125°C
Lead Temperature Range (Soldering, 60 sec) ............ +300°C
PACKAGE TYPE N(Note1) elc UNITS
14-Pm Plastic DIP (P) 76 33 "CAN
1. l, isspecified for worst case mcu nting condition s, Le. . 6))A is specified for device
in socket for P-DIP package.
REV. B
SPECIAL FUNCTION AUDIO PRODUCTS 7-59
SSM-ZOI 5
ELECTRICAL CHARACTERISTICS at VS = :15V, T, = 25°C, R = 33KQ, unless otherwise noted.
SSM-2015
PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS
Vow = 7V F1MS.FIL = 10kf2
G = 1000
1: 1kHz - 0.007 0.01
f=10kf2 - 0.015 0.02
Total Harmonic Distortion THD G = 100 ''/
(Note 1) t: =1kHz - 0.007 0.01 "
t=10kHz - 0.007 0.01
G = 10
f: IkHz - 0.01 0.015
f=10KHz - 0.01 0.015
Inputs Shoned to GND
20kHz Bandwidth
Rams = 33kit
G = 1000 - 0.2 0.3
Input Referred G = 100 - 0.3 0.5
Voltage Nose En G= 10 - 1.1 1.7 “V RMS
(Note 1) RBIAS a 150m
G = 1000 - 0.28 0.45
G = 100 - 0.41 0.65
G " 10 - 1.1 1 ,7
20kHz Bandwidth
_ R = 33kQ - 250 380
”(mfufem Nioise In Rm As = 6st - 200 300 pA RMS
t) ) RB1 AS = 150m - 130 200
R, " R2 = 1am
G a 1000 - 0.1 0.3
Error From Gain Equation AG G " 100 - 0.1 0.3 dB
G = 10 - 0.2 0.8
R, = R, = 10m
G = 1000 - 0.25 2
lnputOtlset Voltage Vos G = 100 - 0.3 7 mV
G = 10 - 3 70
'k1:1IL,, 4 5 15
' BIAS = _ .
InputBias Current 16 Rams = 150kQ _ 1 4 pA
inM = OVSSKQ 0 5 2 5
BIAS = - . .
Input Offset Current los Rams = ISOKQ _ 0.15 th pA
R1 = R2 = 10m
G = 1000 90 100 -
0:00:63";ng CMRR G = 100 70 95 - dB
elec t G = 10 60 75 -
Pytrsypply _ PSRR v = $1210 t17V - 100 - dB
Rejection Ratio s
Common-Mode CMVR t4 t5.5 _ V
Voltage Range
Common-Mode
Input Impedance R'NCM _ 50 - Mn
. . G = 1000 - 0.5 -
ttCttee:, RIN G=100 - s - m
p p G = 10 _ 20 -
OutpuiVoltage Swmg vo RL = 2kf2 :105 t12.5 - V
Output Current I Source 15 25 - mA
(Note 2) OUT Sink 8 14 -
G = 1000 - 150 -
-3dB Bandwidth GBW G = 100 - 700 - kHz
G = 10 - 1000 -
Slew Rate SR - a - V/gs
Supply Current 'sv 8 12 16 mA
NOTES: Specifications subject to change; consult latest data sheet.
1. Parameter is sample tested to maximum limits
2. Output is protected from short otuits to ground or either supply.
7-60 SPECIAL FUNCTIONAUDIO PRODUCTS REV. B
SSM-2015
I" , coup: ms "
A m; mun L
arts , OUT 'IIN " . daupm
' - ssu-zo ' " " l
"w im, 200PF
' " 410 w _ I
ca--'- COHPZ MN tt ' -o-tNPur
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= flu 1% II“
VOLTAGE mm. 'll-. .15 -1sv
FIGURE 1: Typical Application
APPLICATIONS INFORMATION
PRINCIPLE OF OPERATION
Figure 1 shows a typical application for the SSM-2015. This
device operates as a true differential amplifier with feedback
returned directly to the emitters ofthe input stage transistors by
R1. This system produces both optimum noise and common-
mode rejection while retaining a very high input impedance at
both inputterminals, An internal feedback loop maintains the input
stage current at a value controlled by an external resistor (Rams)
from pin14to V-. This provides a programmability function which
allows noiseto be optimizedforsourceimpedances ofupto 4kn.
GAIN SETTING
The nominal gain of the SSM-2015 is given by:
GsRitf3g, +R2 +R-t..tF-k +R2 +1
G = 3033 + 3.5 Form. R2 =10kQ
R, and l, should be equal to 10kn for best results (see Figure
1). It is vital that good quality resistors be used in the gain setting
network, since low quality types (notably carbon composition)
can generate significant amounts of distortion and, under some
conditions, low frequency noise. The SSM-2015 will function at
gains down to 3.5, but the best performance is obtained at gains
above 10.Table1 gives Ra valuestor most commonly used gains.
REV. B
TABLE 1: FIG Values for Commonly Used Gains
= R1 + R
G - 3.5
GAIN Re ERROR
10 3kn +0.14dB
50 4309 +0.002dB
100 200n +0.3dB
500 399 +0.28dB
1000 200 +0.03dB
FREQUENCY COMPENSATION
Referring to Figure 1, c, (50pF) provides compensation far the
input stage current regulator, while C, and ()2 compensate the
overall amplifier. The latter two depend on the value of Rams
chosen. Table 2 shows the recommended values for c, and c,
at various R levels. These values are valid for all gain set-
TABLE 2: Recommended Compensation Values
RBIAS c, c,
27kn - 47m 15pF 15pF
47kn - eakn 15pF 10pF
eskn - 150m 30pF SpF
SPECIAL FUNCTION AUDIO PRODUCTS 7-61
SSM-201 5
The SSM-2015 has a bandwidth of at least 70kHz under worst
case conditions (G = 1000, Rams = 150kQ) and considerably
greater at higher set currents and lower gains. This excellent
performance is supplemented by a highly symmetric slew rate
for optimum large signal audio performance. The SSM-2015
provides stable operation with load capacitances of upto 1 50pF;
larger capacitances should be decoupled with a 100:2 resistor in
series with the output (R, in Figure 1 should remain connected
to pin 3).
- ttm /',"
ii. BALANCEDINPV/
a St 1
3 SINGLE ENDED INPUT
mo 250 500 u 2.5k 5k
SOURCE RESISTANCE (m
FIGURE 2: Optimum R vs. Source Resistance
The programmability ofthe SSM-2015 provides close to optimum
performance for source impedances of up to 4RD, and is within
1dB ofthe theoretical minimum value between 5009 and 2.5k9.
Figure 2 shows the recommended bias resistor (Rams) versus
source impedance, for balanced or single-ended inputs.
INPUTS
Although the SSM-2015 inputs are fully floating, care must be
exercised to ensurethat both inputs have a DC bias connection
capable of maintaining them within the input common-mode
range. The usual method of achieving this is to ground one side
of the transducer as in Figure 3(a), but an alternative way is to
float the transducer and use two resistors to set the bias point is
in Figure 3(b). The value of these resistors can be up to 10kQ,
but they should be kept as small as possible to limit common-
mode noise. Noise generated in the resistors themselves is
negligible since it is attenuated by the transducer impedance.
Balanced transducers give the best noise immunity, and inter-
face directly as in Figure Mc).
TRIMMING
The gain of the SSM-2015 can be easily trimmed by adjustment
of Ra. However, two further trims may be desirable:OffsetVolt-
age and Common-mode Rejection. although the SSM-2015
provides excellent untrimmed performance in both respects.
(INVERHNGI
- - - i 1
ssu-ms " 1 sh.-
= 2MP F--
.5. ' l - s "
(NONINVEWNG)
T L l 2 V
SSM-2015
55%2015
TRANSDUCE R
TRANSDUCE R
FIGURE 3: Three Ways of interfacing Transducers for High Noise Immunity
(a) Single Ended (b) Pseudo Differential (c) True Differential
7-62 SPECIAL FUNCTION AUDIO PRODUCTS
REV. B
SSM-2015
ssu-zms It "
' Ra vn,
n, 915m
FIGURE 4: Trimming the SSM-2015
Figure 4 shows the trimming method for both parameters.
l/n, is the CMR trim and should be adjusted for minimum output
with an 8Vp-p amplitude 60Hz Sine Wave common to both inputs.
l/m, is the offset voltage trim, and should be selected from Table
3. The offset trim should follow the CMR trim, since there is a
small (non-reciprocal) interaction.
The offset trim can also be used to null out the gain control
The offset trim can also be used to null out the gain control
feedthrough. The output offset at low gains is determined by
matching of the feedback resistors while at high gains it is deter-
mined bythe matching of the input resistors. ii the gain setting is
changed rapidly, the output shift can cause an (audible) click or
thump. To reduce or eliminate this, the offset at high gains is
adjusted to be equal to the offset at low gains.
TABLE 3: Recommended Values for the Offset Voltage Trim
27kn - 47kn 47kQ - 68kf2 68kft - 150kQ
G = 10 500kO 250kn 250kQ
G = 100 500kQ 100kg2 IOOKQ
G = 1000 250kQ 100kQ 50kQ
PHANTOM POWER
A recommended circuit for phantom microphone powering is
shown in Figure 5. z, through z, provide transient overvoltage
protection for the SSM-2015 whenevermicrophones are plugged
in and out.
SSM-ZOIS
' 2, - " s.sv doomw
c, - c, 47uF 60V TANTALUM I
FIGURE 5: SSM-2015 with Phantom Power
REV. B
SPECIAL FUNCTION AUDIO PRODUCTS 7-63
