Effects on variation of supply voltage on the sensitivity of the BL

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VOLTAGE ON THE SENSITIVITY OF
THE BL MICROPHONE
The attached graph shows the effect of supply voltage (V ) on BL microphone
output over the voltage range 0.9 to 20.0 volts d.c. S
The "nominal" line illustrates the performance of the "average" BL microphone
coming off of our production lines. Please note, however, that variability
in components and assemblies yield a range of possible sensitivity changes
for each supply voltage. This chart is referenced to our standard speci
fication of a 1.3 volts d.c. supply voltage and indicates the possible change
of output for any single BL microphone as compared to its 1.3 volts sensi
t i v i t y.
As an example, changing Vg from 1.3 volts to 3.0 volts will increase the
lKHz output voltage by 0.3 dB to 2.4 dB for 99% of the BL microphones pre
sently produced. However, 65% to 70% of the product will change only be
tween 0.4 dB and 1.5 dB for this same V„ change.
If the BL microphone is to be used at a lower supply voltage, 0.9 volts for
example, the output loss (relative to the 1.3 volt output) could range from
0.5 to 6.5 dB (normally 1.5 dB) for 65% to 70% of-our production, and the loss
could exceed 10 dB for about 12% to 15% of our present production.
We guarantee, by 100% testing, that all BL microphones will not exhibit more
than a 3 dB loss at 1.1 volts dc compared to the 1.3 volts output for that
unit.
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IMPORTANT NOTE:
The graph is useable only for general application perspective
and must not be used to generate specifications or limits.
KNOWLES ELECTRONICS. INC.
3100 N. MANNHEIM ROAD • FRANKLIN PARK. ILL. 60131 » U.S.A.
TELEPHONES (312) 455-3600 • CABLE - KNOLEC CHICAGO • TELEX-25-3387
101
NEW TELEX NUMBER 72-8397
BL-5
EFFECTS Or vAaiAHOM Uj: dvf?LY
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VOLTAGE ON THE SENSITIVITY OF
THE BL MICROPHONE
1 KHz SENSITIVITY CHANGE
VS.
DC SUPPLY VOLTAGE
For All BL Models
(Data Based on Random Sampling)
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Vs DC SUPPLY VOLTAGE
(Logarithmic Scale)
KNOWLES ELECTRONICS, INC.
3100 N. MANNHEIM ROAD • FRANKLIN PARK, ILL. 60131 • U.S.A.
TELEPHONES (312) 455-3600 • CABLE — KNOLEC CHICAGO • TELEX-25-3387
NEW TELEX NUMBER 72-8397
S-083-566
101
BL-5
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APPLICATION NOTES
BL Series Microphones
General Description; A line of subminiature, piezoelectric microphones with
i n t e g r a l a m p l i fi e r s t a g e f o r a p p l i c a t i o n s r e q u i r i n g h i g h s e n s i t i v i t y, w i d e
frequency range, small size, and high mechanical shock resistance. The sen
sitivity of these microphones is high enough so that a transistor stage can be
omitted in some applications.
Typical Dimensions;
(in inches)
BL-1670 Series
BL-1680 Series
Length
.312 max.
.312 max.
Width
.220 max.
.220 max.
Thickness
.163 max.
.090 max.
Nominal Sensitivity at 1000 Hertz re; 1 Volt/microbar with a Supply Voltage
of 1.3 Volts DC:
BL-1670
BL-1671
BL-1672
-55.0dB
-54.5dB
-54.5dB
BL-1680
BL-1681
BL-1682
-57.5dB
-57.5dB
-57.5dB
Note: A change from 1.3 to 1.1 Volts DC shall cause not more than a 3.0d3
decrease in 1 KHz output.
Nominal Impedance at 1000 Hertz: 13,000 ohms. (Range: 8,000 to 22,000 ohms.)
Battery Drain at 1.3 Volts DC: 50 microamps maximum.
DC Voltage at Output Terminals (See Fig. 1):
Negative Terminal Common - 0.2 to 0.9 Volts DC
Positive Terminal Common - -0.4 to -1.1 Volts DC
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model number and date code
on this side
Figure 1 (Negative Terminal Common)
Case Grounding; No greater than 100 ohms DC resistance between case and
negative terminal.
KNOWLES ELECTRONICS. INC.
3100 N. MANNHEIM ROAD • FRANKLIN PARK, ILL. 60131 • U.S.A.
TELEPHONES (312) 455-3600 • CABLE - KNOLEC CHICAGO • TELEX-25-3387
NEW TELEX NUMBER 72-8397
171
BL-7
APPLICATION NOTES
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BL Series Microphones
Application; The circuit of Figure 2 will allow these units to be connected in
place of most two-wire microphones. A load resistor %, may be necessary to
reduce the sensitivity to a suitable level, and will produce a DC current
path for those circuits which presently depend on one through the microphone.
Table 1 below provides a rough guide to the value of %, required for a given
reduction in sensitivity for all models. Low frequency response may be reduced
by using coupling capacitor values of less than 1 mfd.
_ . , Ta b l e 1
Approximate
Sensitivity
Reduction (dB)
\ (ohms)
-=Jr--1.3Volts
To A m p l i fi e r
Input
*L
Figure 2
oo
0
5
10
15
20
15K
7K
3K
1.5K
Since the microphone will be connected to the power supply, a portion of any
alternating voltage present on the power supply (fed back from the amplifier)
will appear at the output terminal of the microphone. This power supply feedthrough should be taken into account in the design of the amplifier, as it may
affect the frequency response and stability of the amplifier.
Range of power supply feedthrough (e0/e^n) in Figure 3:
Negative Terminal Common: -17dB to -6dB
....
.
.
...
Positive
Te r m i n a l
Common:
-
ldB
to
-
6dB
-J^ 1.3Volts
rti
Sj'| ein = lOmV
lap
Figure 3
An RC decoupling network in series with the positive lead can be used to
attenuate this effect. The suggested maximum value of R is 2000 ohms (to avoid
excessive voltage drop at the BL terminals). The appropriate value of C can
be determined experimentally.
KNOWLES ELECTRONICS. INC.
3100 N. MANNHEIM ROAD • FRANKLIN PARK, ILL. 60131 • U.S.A.
TELEPHONES (312) 455-3600 • CABLE - KNOLEC CHICAGO • TELEX-25-3387
171
WY
NEW TELEX NU.
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