Hearing-aid with integrated circuit electronics

A hearing-aid has an electronic voltage stabilizing circuit (16) to compensate for change in supply voltage due to battery (18) aging and use. The electret microphone (11) is located within a housing, the voltage stabilizing circuit (16) being located within the same microphone housing, thus requiring no additional space or terminal connections. Preferably, an impedance transformer is provided; the electronic components (31-34) are placed on the same semi-conductor chip as the components (35, 36) of the voltage stabilizing circuit.

The present invention relates to a hearing-aid, particularly of the 
electret-microphone type, and more particularly to a hearing-aid with an 
integral miniaturized voltage stabilizer circuit manufactured by 
integrated circuit technology. 
BACKGROUND 
A hearing-aid device with electret-microphone has been described in Bosch 
Publication No. 6 DRV, and in VKD No. 8 699 944 398-1131. Such a 
hearing-aid requires a voltage stabilizer circuit, which is connected in 
parallel to the battery powering the hearing-aid. The discrete components 
of the stabilizer circuit are located, on the common behind-the-ear-type 
of hearing-aid, on a printed circuit board. Space restrictions on the 
crowded circuit board place a lower limit on the possible size of such a 
hearing-aid and also limit the possibilities of upgrading the device 
performance by addition of further features. 
THE INVENTION 
It is an object to provide the hearing-aid with a voltage stabilizer 
circuit which requires no increase in overall volume of the device. 
Briefly, the hearing-aid includes a microphone, preferably of the electret 
type which is located within the microphone structure. The voltage 
stabilizer circuit is built by integrated circuit technology on a single 
semiconductor chip and located within the hearing-aid structure. An 
impedance transformer preferably is used, which may employ a field effect 
transistor (FET). The FET can thus also be located on the same single 
integrated circuit chip together with the voltage stabilizer circuit and 
the various other active and passive components of the electret 
microphone. The voltage stabilizer circuit is important in order to 
compensate for decreasing voltage supplied by the device battery due to 
battery aging and use.

The hearing-aid device 10--see the block circuit diagram of FIG. 
1--preferably of the type carried behind the ear, has a microphone 11. 
Microphone 11 preferably is of the electret microphone type. The 
structure, or housing thereof is shown by chain dotted lines 12. 
Microphone 11 has three electric terminals 13, 14, 15. The structure 12 
has a voltage stabilizer circuit 16 connected between terminals 13 and 15. 
Terminal 13 is connected through a series resistor 17 with one terminal, 
for example the positive pole terminal of battery 18; terminal 15 is 
connected directly to the other pole, then the negative of battery 18, to 
provide a circuit voltage U.sub.B. Terminal 14, which carries the variable 
signal voltage output from microphone 11, is connected to the input side 
of a preamplifier 20, which is itself connected, through the output 
amplifier 21 to the earphone 22 of the hearing-aid device. 
Terminals 23 and 24 of the output 21 are in direct connection with battery 
18, receiving d-c voltage U.sub.B. Terminal 25 of the preamplifier 20 is 
connected to the positive pole of the battery through series resistor 17 
and terminal 26 is directly connected to the negative pole of the battery 
15. 
FIG. 2 shows details of the circuit contained within the structure 12 of 
microphone 11. In FIG. 2, the microphone is denoted by 30 and represented 
for simplicity as an alternating current source. One side of the 
microphone 30 is connected through capacitor 31 to the gate electrode of 
FET 32, while the other side of the microphone 30 is connected to the 
source electrode of FET 32, and the drain electrode of FET 32 is connected 
to terminal 13. The source electrode of the FET 32 is directly connected 
to terminal 14 and is connected through resistor 33 with terminal 15 and 
through resistors 33 and 34 with the gate electrode of FET 32. The voltage 
stabilizing circuit between terminals 13 and 15 comprises a transistor 35 
and a diode 36. The diode 36 may in fact be constructed in form of a 
second transistor whose collector is left unconnected to the circuit. The 
collector and emitter of the first transistor 35 are electrically in 
parallel to terminals 13 and 15, while the collector and base of 
transistor 35 are connected to the base and emitter, respectively, of the 
transistor 36 which forms the diode in the voltage stabilizing circuit 16. 
OPERATION 
The FET 32 serves as an impedance transformer, to match the high impedance 
of the microphone system 30 to the input impedance of the preamplifier 20. 
The voltage stabilizing circuit 16 is intended to insure that the FET 32, 
the preamplifier 20 and the output amplifier 21 remain at a nearly 
constant supply voltage despite decreasing battery voltage due to battery 
aging. Since the voltage stabilizing circuit is located within the 
structure 12 of microphone 11, its introduction into the device requires 
no additional volume. The semiconductor components 35 and 36 of the 
voltage stabilizing circuit 16 and of the FET 32, as well as resistors 33 
and 34 and capacitor 31 are preferably integrated on a single chip by use 
of integrated circuit technology. The circuits of the pre- and output 
amplifiers 20 and 21, respectively, can then be made by well known methods 
and to standard dimensions well established for a hearing-aid. 
Various changes and modifications may be made within the scope of the 
inventive concept.