Patent Grant
9866959
This application claims the benefit of European Patent Application Serial No. 16152518.3, filed Jan. 25, 2016, which is incorporated herein by reference in its entirety.
The present invention relates to a self-biasing output booster amplifier and the use thereof in connection with for example a sensor module.
Various electronic filter arrangements for processing signals in hearing devices have been suggested over the years. Examples of such arrangements can for example be found in US 2014/0097906 A1, U.S. Pat. No. 6,888,408 B1, GB 2 266 021 A as well as the paper titled “An enhanced slew rate source follower”, IEEE Journal of solid-state circuits (Vol 30, No 2, 1 Feb. 1995, pages 144-146) by Kenney J G et al.
Referring now to US 2014/0097906 A1 an amplifier having a high-pass filter is suggested. However, this high-pass filter has a major drawback in that its cut-off frequency is not constant with an input signal level to the amplifier. Thus, when a large low frequency signal is introduced to the input the amplifier loses partly its high-pass filter function. As a result the low frequency input signal is feed through to the output of the amplifier without the predetermined and constant attenuation. This lack of attenuation will inevitably result in a poor sound quality in the low-frequency range.
U.S. Pat. No. 6,888,408 B1 discloses a high-pass filter suffering from the same problem due to a resistance biasing at the input stage of the amplifier, i.e. bias current varies with output signal level. Moreover, the output noise level of the arrangement suggested in U.S. Pat. No. 6,888,408 B1 is high, because a common source n-channel metal-oxide-semiconductor (NMOS) output stage is used instead of a common source p-channel metal-oxide-semiconductor (PMOS) transistor.
The above-mentioned disadvantages regarding the high-pass filter also apply to GB 2 266 021 A and the paper of Kenney J G et al.
Thus, there seems to be severe disadvantages associated with the high-pass filters suggested in the above-mentioned prior art references.
It may be seen as an object of embodiments of the present invention to provide an amplifier topology that facilitates incorporation of a stable filter stage having a frequency response which is essentially unaffected by a signal level arriving at an input amplifier stage of the amplifier.
It may be seen as a further object of embodiments of the present invention to apply the amplifier in an advantageous configuration in a microphone unit in order to obtain a dual omni-output signal.
The above-mentioned objects are complied with by providing, in a first aspect, a self-biasing output booster amplifier comprising
The self-biasing concept of the output booster amplifier of the present invention facilitates that the output booster amplifier may advantageously be used in two wire applications. In the present context the term “self-biasing” implies that the output booster amplifier will balance its internal bias currents through its components itself via a negative feedback path.
As addressed above the output amplifier stage may be operatively connected to an output of the input amplifier stage. The term “operatively” should be understood as either directly connected or connected via for example a filter stage, such as a via a high-pass filter.
The self-biasing output booster amplifier according to the present invention is advantageous over prior art systems in various ways. Firstly, the self-biasing output booster amplifier of the present invention may apply a fixed external bias current source. This facilitates use in particular in relation to two wire amplifier configurations. The circuit topology of the self-biasing output booster amplifier facilitates implementation and integration of a stabile high pass filter. Due to the circuit topology a low frequency signal at the input stage output will have less feed through to the output node. The self-biasing output booster amplifier currents flow through the current mirrors and the output stage and contribute directly to the output signal level. No other fixed current source is required inside the self-biasing output booster amplifier circuit. This may reduce the supply current efficiency which is ideal for lower power applications.
The topology of the self-biasing output booster amplifier of the present invention is advantageous in that its frequency response is essentially unaffected by the level of an input signal applied to an input amplifier stage of the self-biasing output booster amplifier.
The self-biasing output booster amplifier of the present invention may in principle handle any kind of input signal, including input signals from various types of sensors, such as vibration sensors, pressure sensors, microphones etc.
The first and second current copying circuits may be configured to copy the total current through the output amplifier stage. In addition, the input amplifier stage may be fully biased from the output of the second current copying. The self-biasing output booster amplifier may further comprise a power supply comprising a bias current source.
The output amplifier stage of the self-biasing output booster amplifier may comprise a source follower. The source follower may comprise a transistor, such as a PMOS or a NMOS type transistor. It should be noted however, that the source follower may be replaced by other circuit topologies, such as other types of amplifier states, operational amplifier configurations etc.
The input amplifier stage may comprise at least one transistor being adapted to be operated as a source follower stage in order to buffer an incoming signal from the associated sensor, such as vibration sensors, pressure sensors, microphones etc. The at least one transistor may be a PMOS or a NMOS transistor.
The current copying circuit may comprise a current mirror circuit for sensing a drain current from a source follower, and wherein a copy of the drain current is applied to control one or more currents through one or more current sources of the self-biasing output booster amplifier. Thus, a drain current of the output amplifier stage may be copied and subsequent applied to control one or more currents through one or more current sources of the self-biasing output booster amplifier. Again, the one or more current sources may comprise transistor-based circuit topologies.
As indicated above the self-biasing output booster amplifier may further comprise an input amplifier stage adapted to receive a signal from an associated sensor. Moreover, the self-biasing output booster amplifier may further comprise a filter stage adapted to filter signals from the input amplifier stage. The filter stage may comprise a high-pass filter, a low-pass filter, a band-pass filter or a notch filter. The presence of the current copying circuit ensures that the frequency response of the filter stage, and thereby the frequency response of the self-biasing output booster amplifier as a whole, is essentially unaffected by the level of an input signal applied to the input amplifier stage.
The output amplifier stage of the self-biasing output booster amplifier may further comprise a voltage level shifting arrangement, such as a resistor. The resistance of such a resistor may be selected in view of an acceptable noise level. In fact the voltage level shifting arrangement may be considered as forming an integral part of the output amplifier stage.
In a second aspect the present invention relates to a summing circuit for processing signals from at least two associated sensors, said summing circuit comprising a plurality of self-biasing output booster amplifiers according to the first aspect of the present invention. The number of applied self-biasing output booster amplifiers may in principle be arbitrary. Typically, the number of self-biasing output booster amplifiers will however be smaller than 10, such as smaller than 8, such as smaller than 6. The at least two associated sensors may comprise at least two microphone membranes, such as MEMS membranes and/or electret membranes.
In a third aspect the present invention relates to a sensor module comprising at least one summing circuit according to the second aspect, and at least one sensor being operatively connected thereto. The at least one sensor may be selected from the group consisting of: microphones, telecoils and vibration sensors.
In a fourth aspect the present invention relates to a microphone module comprising at least one summing circuit according to the second aspect, and at least one microphone cartridge being operatively connected thereto, wherein the at least one microphone cartridge may comprise a MEMS cartridge and/or an electret cartridge.
In a fifth aspect the present invention relates to a personal assisting device comprising a sensor module according to the third aspect, said personal assisting device comprising a hearing aid being selected from the group consisting of: behind-the-ear, in-the-ear, in-the-canal and completely-in-the-canal.
In a sixth aspect the present invention relates to a method for operating a self-biasing output booster amplifier, the method comprising the steps of copying a current from an output amplifier stage, and control one or more currents through one or more current sources of the self-biasing output booster amplifier using the copied current. The copied current may be a drain current from a source follower. The output amplifier stage may comprise a first and a second gain. The first and second gains may be generated by respective first and second amplifier stages. Moreover, the first and second gains being adjustable, such as adjustable by hard-wiring on beforehand and/or adjustable on-the-fly, i.e. during operation of the output booster amplifier.
The present invention will now be described in further details with reference to the accompanying figures, wherein
While the invention is susceptible to various modifications and alternative forms specific embodiments have been shown by way of examples in the drawings and will be described in details herein. It should be understood, however, that the invention is not intended to be limited to the particular forms disclosed. Rather, the invention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention as defined by the appended claims.
In its broadest aspect the present invention relates to an amplifier circuit having a frequency response which is essentially unaffected by a signal level arriving at an input amplifier stage of the amplifier circuit. The amplifier circuit may have a filter stage incorporated therein. The amplifier circuit is implemented in such a way that the filter stage is essentially unaffected by a signal level being provided to an input amplifier stage of the amplifier circuit. The amplifier circuit of the present invention is of the type two wire self-biasing output booster amplifier.
Referring now to
The high-pass filter stage 220 comprises a capacitor 221 and a resistor 222. The cut-off frequency of the high-pass filter will typically be in the frequency range 20-300 Hz.
The two wire self-biasing output booster amplifier further comprises an output stage comprising a transistor 223 and resistor 224. The transistor 223 acts as a source follower stage and thereby steers the output node with the desired output signal level. The resistor 224 acts as a bias level shift to increase the Vdcout level 225. The resistance of the resistor 224 may typically be set to be between 0Ω (no resistor present) to around 100 kΩ—the upper limit being set in view of noise considerations. With an increase in the Vdcout level 225 the input overload margin of the input amplifier stage increases accordingly. Moreover, the output impedance of the amplifier is more constant as a function of signal levels, which result in a more constant low-pass filter frequency. A low-pass filter (not shown) in the form of a capacitor being directly connected between the output 225 and ground node 230 would normally also be provided. This capacitor is normally is in the range of 1 pF to 20 nF.
The self-biasing output booster amplifier circuit is implemented using a current mirror feedback loop via transistors 226, 227, 228, 229. These transistors are arranged in such a manner that the currents in all three branches of the amplifier circuit are steered by input signal. The feedback loop ensures that the ratio between the DC biasing and any AC signal current in all three branches of the amplifier circuit is fixed. The gain from the input 219 to the output 225 is mainly given by the output stage source follower gain, i.e. transistor 223 and resistor 224. The output current of the output stage source follower is copied to ensure that the current in the other two branches including transistor 227 and 228 follows the output current, i.e. boosting the total output current.
Moreover, the branch including transistor 223 carries a smaller portion of the total output signal current due to the current copy via the other branches containing transistor 227 and 228. This smaller current portion makes the transistor 223 behave more linear.
It should be noted that by replacing the resistor 222 in the high-pass filter stage 220 with a capacitor and an antiparallel diode network the high-pass filter function can be removed. The gain curve will then not have a high-pass filter characteristic. Instead the response will ideally be flat in the frequency range between 20 Hz and 1 kHz.
A comparison of the response of the two wire self-biasing output booster amplifier of the present invention and a typical prior art circuit is shown in
As seen in
Another way to look at the high-pass filter response is to consider an AC gain simulation result at different voltage bias levels of the first amplifier stage PMOS transistor 201, cf.
1)
2)
3)
The above-mentioned input signal levels are applied to both a typical prior art circuit and the amplifier circuit of the present invention.
In
In
In
In conclusion, for mid (1 kHz) and high (5 kHz) frequencies the THD levels of the two circuits are comparable. For the 50 Hz input signal the responses from the two circuits 501, 502 are clearly different. However, it should be noted that the THD's levels may vary with the exact circuit topology applied.
Another advantageous feature of the amplifier circuit of the present invention relates to the fact that amplifier circuit is capable of operating using a wide range of DC bias current. In fact the amplifier circuit of the present invention is capable of handling DC bias currents ranging from 5 μA to 20 μA while maintaining an essential constant AC response and low THD levels, cf.
In
The input signal frequency is swept between 1 kHz and 1 MHz. As seen in
The self-biasing output booster amplifier of the present invention may be used in various applications. In case of directional microphone systems for use in a hearing device it would be beneficial to have a microphone module which not only has the regular (either front/rear/directional) microphone outputs but also has an output signal node where a dual omni-directional signal is available. By incorporating a summing functionality into the microphone module the generation of the dual omni-directional signal may be performed close to the first amplifier stage in the signal chain. This is advantageous due to an improved SNR compared to adding the signals inside the DSP which is several amplifier stages down the signal stage.
To provide the above-mentioned functionality within a microphone module a circuit that buffers and sums two electrical signals coming from two microphone membranes is required. The main feature of such a new buffering and summing circuit would be to generate a summed signal from two inputs signals V(A) and V(B) using the following relation:
V(out)=Gamp1V(A)+Gamp2V(B)
or
V(out)=Gamp(V(A)+V(B))
if the gains, Gamp, of the amplifiers are equal. Otherwise Gamp1 and Gamp2 are the gains of the respective amplifiers.
A suitable buffering and summing circuit is depicted in
Still referring to
The two input nodes 703, 704 could also be connected to the same microphone membrane. In this scenario a high gain signal path and a low gain signal path may be provided through the respective amplifiers 701, 702. This allows that either the high gain signal path or the low gain signal path may be selected. An advantage associated with such as arrangement would be to have a more click and pop free audio signal during switching between the high and the low gain mode of operation.
As already addressed the amplifiers 701, 702 are of the type two wire self-biasing output booster amplifier, cf.
One way to arrive at the desired buffering and summing, the nodes 707, 708 of the amplifiers 701, 702 need to be connected. The nodes 707, 708 going internally into the respective amplifiers 701, 702 are connected to either node 204, 204′, 212 or 212′ of the current copying circuits 203, 211 of
In the buffering and summing circuit shown in
Still referring to
The second function of the connection via the add nodes 707 is to sum the AC signal currents resulting from input signals provided at input nodes 703, 704 such that both first and second current copying circuits in both amplifiers 701, 702 can boost the output node 705 with the AC summed signal.
Returning now to
Referring now to
As indicated by the dotted line 1005 the input amplifier stages 1010, 1011 may optionally be connected. Each of the first and second stages processes respective parts of the total frequency range.
Referring now to
Referring now to
| Number | Date | Country | Kind |
|---|---|---|---|
| 16152518 | Jan 2016 | EP | regional |
| Number | Name | Date | Kind |
|---|---|---|---|
| 6788796 | Miles et al. | Sep 2004 | B1 |
| 6831577 | Furst | Dec 2004 | B1 |
| 6853290 | Jorgensen et al. | Feb 2005 | B2 |
| 6859542 | Johannsen et al. | Feb 2005 | B2 |
| 6888408 | Furst et al. | May 2005 | B2 |
| 6914992 | van Halteren et al. | Jul 2005 | B1 |
| 6919519 | Ravnkilde et al. | Jul 2005 | B2 |
| 6927634 | Kobayash | Aug 2005 | B1 |
| 6930259 | Jorgensen et al. | Aug 2005 | B1 |
| 6943308 | Ravnkilde et al. | Sep 2005 | B2 |
| 6974921 | Jorgensen et al. | Dec 2005 | B2 |
| 7008271 | Jorgensen | Mar 2006 | B2 |
| 7012200 | Moller | Mar 2006 | B2 |
| 7062058 | Steeman et al. | Jun 2006 | B2 |
| 7062063 | Hansen et al. | Jun 2006 | B2 |
| 7072482 | Van Doom et al. | Jul 2006 | B2 |
| 7088839 | Geschiere et al. | Aug 2006 | B2 |
| 7110560 | Stenberg | Sep 2006 | B2 |
| 7136496 | van Halteren et al. | Nov 2006 | B2 |
| 7142682 | Mullenbom et al. | Nov 2006 | B2 |
| 7181035 | van Halteren et al. | Feb 2007 | B2 |
| 7190803 | van Halteren | Mar 2007 | B2 |
| 7206428 | Geschiere et al. | Apr 2007 | B2 |
| 7221767 | Mullenborn et al. | May 2007 | B2 |
| 7221769 | Jorgensen | May 2007 | B1 |
| 7227968 | van Heltren et al. | Jun 2007 | B2 |
| 7239714 | de Blok et al. | Jul 2007 | B2 |
| 7245734 | Niederdraenk | Jul 2007 | B2 |
| 7254248 | Johannsen et al. | Aug 2007 | B2 |
| 7286680 | Steeman et al. | Oct 2007 | B2 |
| 7292700 | Engbert et al. | Nov 2007 | B1 |
| 7292876 | Bosh et al. | Nov 2007 | B2 |
| 7336794 | Furst et al. | Feb 2008 | B2 |
| 7365604 | Luo | Apr 2008 | B2 |
| 7376240 | Hansen et al. | May 2008 | B2 |
| 7403630 | Jorgensen et al. | Jul 2008 | B2 |
| 7415121 | Mögelin et al. | Aug 2008 | B2 |
| 7425196 | Jorgensen et al. | Sep 2008 | B2 |
| 7460681 | Geschiere et al. | Dec 2008 | B2 |
| 7466835 | Stenberg et al. | Dec 2008 | B2 |
| 7492919 | Engbert et al. | Feb 2009 | B2 |
| 7548626 | Stenberg et al. | Jun 2009 | B2 |
| 7657048 | van Halteren et al. | Feb 2010 | B2 |
| 7684575 | van Halteren et al. | Mar 2010 | B2 |
| 7706561 | Wilmink et al. | Apr 2010 | B2 |
| 7715583 | Van Halteren et al. | May 2010 | B2 |
| 7728237 | Pedersen et al. | Jun 2010 | B2 |
| 7809151 | Van Halteren et al. | Oct 2010 | B2 |
| 7822218 | Van Halteren | Oct 2010 | B2 |
| 7899203 | Van Halteren et al. | Mar 2011 | B2 |
| 7912240 | Madaffari et al. | Mar 2011 | B2 |
| 7946890 | Bondo et al. | May 2011 | B1 |
| 7953241 | Jorgensen et al. | May 2011 | B2 |
| 7961899 | Van Halteren et al. | Jun 2011 | B2 |
| 7970161 | van Halteren | Jun 2011 | B2 |
| 8098854 | van Halteren et al. | Jan 2012 | B2 |
| 8101876 | Andreasen et al. | Jan 2012 | B2 |
| 8103039 | van Halteren et al. | Jan 2012 | B2 |
| 8160290 | Jorgensen et al. | Apr 2012 | B2 |
| 8170249 | Halteren | May 2012 | B2 |
| 8189804 | Hruza | May 2012 | B2 |
| 8189820 | Wang | May 2012 | B2 |
| 8223996 | Beekman et al. | Jul 2012 | B2 |
| 8233652 | Jorgensen et al. | Jul 2012 | B2 |
| 8259963 | Stenberg et al. | Sep 2012 | B2 |
| 8259976 | van Halteren | Sep 2012 | B2 |
| 8259977 | Jorgensen et al. | Sep 2012 | B2 |
| 8280082 | van Halteren et al. | Oct 2012 | B2 |
| 8284966 | Wilk et al. | Oct 2012 | B2 |
| 8313336 | Bond et al. | Nov 2012 | B2 |
| 8315422 | van Halteren et al. | Nov 2012 | B2 |
| 8331595 | van Halteren | Dec 2012 | B2 |
| 8369552 | Engbert et al. | Feb 2013 | B2 |
| 8379899 | van Halteren et al. | Feb 2013 | B2 |
| 8509468 | van Halteren et al. | Aug 2013 | B2 |
| 8526651 | Lafort et al. | Sep 2013 | B2 |
| 8526652 | Ambrose et al. | Sep 2013 | B2 |
| 20020067209 | Luo | Jun 2002 | A1 |
| 20090302824 | Kim | Dec 2009 | A1 |
| 20110182453 | van Hal et al. | Jul 2011 | A1 |
| 20110189880 | Bondo et al. | Aug 2011 | A1 |
| 20110299708 | Bondo et al. | Dec 2011 | A1 |
| 20110299712 | Bondo et al. | Dec 2011 | A1 |
| 20110311069 | Ambrose et al. | Dec 2011 | A1 |
| 20120014548 | van Halteren | Jan 2012 | A1 |
| 20120027245 | van Halteren et al. | Feb 2012 | A1 |
| 20120140966 | Mocking et al. | Jun 2012 | A1 |
| 20120155683 | van Halteren | Jun 2012 | A1 |
| 20120155694 | Reeuwijk et al. | Jun 2012 | A1 |
| 20120250898 | Wang et al. | Oct 2012 | A1 |
| 20120255805 | van Halteren et al. | Oct 2012 | A1 |
| 20130028451 | de Roo | Jan 2013 | A1 |
| 20130136284 | van Hal et al. | May 2013 | A1 |
| 20130142370 | Engbert et al. | Jun 2013 | A1 |
| 20130163799 | Van Halteren | Jun 2013 | A1 |
| 20130195295 | van Halteren et al. | Aug 2013 | A1 |
| 20140097906 | Jennings et al. | Apr 2014 | A1 |
| Number | Date | Country |
|---|---|---|
| 2266021 | Oct 1993 | GB |
| Entry |
|---|
| European Search Report corresponding to European Patent Application No. 16152518, European Patent Office, dated Jul. 7, 2016; (2 pages). |
| Kenney et al., An Enhanced Slew Rate Source Follower, XP000496306, 8107 IEEE Journal of Solid-State Circuits (Feb. 30, 1995), No. 2, New York, US; dated 1995; (3 pages). |
| Number | Date | Country | |
|---|---|---|---|
| 20170215006 A1 | Jul 2017 | US |
