Patent Publication Number: US-9843314-B2

Title: Pop and click noise reduction

Description:
RELATED APPLICATIONS 
     This application is a continuation of U.S. patent application Ser. No. 13/540,920, filed Jul. 3, 2012, now U.S. Pat. No. 9,225,293, which claims priority to and benefit of U.S. Provisional Patent Application Ser. No. 61/506,135, filed on Jul. 10, 2011, which is hereby incorporated by reference for all purposes as if set forth herein in its entirety. 
    
    
     TECHNICAL FIELD 
     The invention relates to apparatus for controlling the output of circuits and systems. More particularly, the invention relates to apparatus for reducing pops and clicks caused by the initial application of power to load elements in electronic systems. 
     BACKGROUND OF THE INVENTION 
     For audio power amplifiers, pop and click noises during power-up and power-down of systems is undesirable and irritating to users. For amplifiers using only a single power supply, the speaker is often biased at mid-rail. However, prior to powering up the system, the voltage on the output of the amplifier and on the speaker terminals is at 0V. This is further complicated with class-D amplifiers, for example, that use inductors, resistors, and capacitors to filter the switching frequency, as these components require charging up from an off state, e.g., 0V, as well. This problem extends to other electronic circuits and systems in addition to audio circuits, such as data transmittal systems for example. 
     Due to these and other problems and potential problems with the current state of the art, improved apparatus for controlling output to load elements and preventing or attenuating pops and clicks in electronic systems would be a useful and advantageous contribution to the art. 
     SUMMARY OF THE INVENTION 
     In carrying out the principles of the present invention, in accordance with preferred embodiments, the invention provides advances in the arts with novel apparatus and associated methods directed to useful and advantageous improvements to electronic systems. 
     According to one aspect of the invention, an example of a preferred embodiment of pop and click reduction in a circuit includes a load element with its terminals connected to a bridge circuit. An op amp circuit is used for bringing the terminals of the load element to a selected voltage level, such as mid-rail. The circuit is configured such that the op amp output is turned on in the absence of a load signal and turned off when a load signal is present. 
     According to another aspect of the invention, in an exemplary embodiment a reduced pop and click circuit includes an op amp circuit connected within the circuit for bringing the terminals of a load element to a selected voltage level. The op amp receives feedback from a load terminal and turns off when the load receives a signal at the output node of the bridge circuit. 
     According to another aspect of the invention, in an exemplary embodiment, an electronic circuit includes a load circuit including at least a load element and first and second terminals, each of which includes a capacitor. A bridge circuit has an output node connected to the load circuit. An op amp is situated to receive an input signal and to supply an output signal to bring the terminals of the load to a selected voltage level. The op amp receives feedback from a load terminal and turns off when the voltage level at the load circuit is not zero. 
     According to another aspect of the invention, in an example of a preferred embodiment, an electronic circuit has a load element. A bridge circuit has an output node connected with one load terminal and a feedback node connected with a second load terminal. A first op amp is provided for receiving an input signal and for supplying an output signal to the bridge circuit feedback node, and for also supplying the same output signal as an input to a second op amp coupled for providing an output signal to the bridge circuit output node. The op amp output signals are used to bring the terminals of the load to a selected voltage level without transiting the load element. 
     According to another aspect of the invention, in an exemplary embodiment, a selector circuit is included for selecting either an output signal from an external origin destined for the load or a wave-shape signal for transmittal to the terminals of a load element. 
     According to yet another aspect of the invention, an example of a preferred embodiment includes a selector circuit for selecting either an externally provided load signal or a wave-shape signal for transmittal to the terminals of a load. The circuit also includes an op amp electrically connected with one or more load terminal in a configuration adapted for selection from among an op amp output signal, external signal, or internal class-D output signal. 
     The invention has advantages including but not limited to providing reductions in pop and click noise in an electronic system. This and other advantageous features and benefits of the present invention can be understood by one of ordinary skill in the arts upon careful consideration of the detailed description of representative embodiments of the invention in connection with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention will be more clearly understood from consideration of the following detailed description and drawings in which: 
         FIG. 1  is a simplified schematic diagram depicting an example of a preferred embodiment of an electronic circuit having pop and click noise reduction according to the invention; 
         FIG. 2  is a simplified schematic diagram illustrating another example of a preferred embodiment of an electronic circuit having pop and click noise reduction according to the invention; 
         FIG. 3  is a simplified schematic diagram of a preferred embodiment of the invention in another example of an electronic circuit having pop and click noise reduction; 
         FIG. 4  is a simplified schematic diagram representing further examples of preferred embodiments of electronic circuits having pop and click noise reduction according to the invention, and 
         FIG. 5  is a diagram of an exemplary embodiment of the present invention. 
     
    
    
     References in the detailed description correspond to like references in the various drawings unless otherwise noted. Descriptive and directional terms used in the written description such as front, back, top, bottom, upper, side, et cetera; refer to the drawings themselves as laid out on the paper and not to physical limitations of the invention unless specifically noted. The drawings are not to scale, and some features of embodiments shown and discussed are simplified or amplified for illustrating principles and features, as well as advantages of the invention. 
     DESCRIPTION OF PREFERRED EMBODIMENTS 
     While the making and using of various exemplary embodiments of the invention are discussed herein, it should be appreciated that the present invention provides inventive concepts which can be embodied in a wide variety of specific contexts. It should be understood that the invention may be practiced with various audio systems and functionally similar non-audio systems in which initial voltage control is desirable without altering the principles of the invention. The examples of circuits and techniques shown and described herein are representative embodiments, and may be used in various combinations. For purposes of clarity, detailed descriptions of functions, components, and systems familiar to those skilled in the applicable arts are not included. In general, the invention provides novel and advantageous advances in terms of improving systems by providing standby voltage to output devices, such as audio speakers for example, in order to smooth the transition from an inactive to an active state. 
     Referring initially to  FIG. 1 , an example of a preferred embodiment of a pop and click noise reduction circuit  100  implementing the invention in the context of a class D amplifier is shown in a simplified schematic. A single-ended half-H bridge configuration  102  has an output node  104  and a feedback node  106  connected to the respective terminals  108 ,  110 , of a load element, in this case a speaker  112 . Other bridge circuits such as full bridge circuits may also be used. An analog modulator  114  is provided with gate drives  116 ,  118  connected to the output node  104  using suitable diodes  120 ,  122  in an arrangement suitable for driving the load element  112 . An op amp  124  is provided for bringing the terminals  108 ,  110  of the speaker  112  to a mid-rail voltage level, in this example  15 V. The circuit  100  is designed to charge the capacitors C 1  and C 2  located at the speaker  112  terminals  108 ,  110  to a selected level, while avoiding or attenuating transient current through the speaker  112  during this charging process. When a system (not shown) associated with the circuit  100  is powered up from an “off” state, the half-H bridge section  102  is also “off” (high-impedance state). In this state, the op amp  124  operates to charge the terminal  110 , through the feedback node  106 , to the mid-rail voltage level. Input to the op amp  124  is preferably provided by a wave-shape circuit block  126 . The op amp  124  receives its feedback signal from the half-H bridge  102  output node  104 , which is after the passive components L 1 , C 1 , and C 2 , around the speaker  112 . In a suitable alternative arrangement, the feedback signal to the op amp  124  may also be taken directly from the half-H bridge  102  feedback node  106 . A particular advantage may be realized by charging C 2  through the feedback node  106  in the event that a large capacitor is used at C 2 . By charging C 2  directly, the current flow through the speaker  112  is reduced. The shape of the waveform of the op amp  124  output signal provided at the speaker  112  is controlled by the wave-shape circuit  126 , which can be implemented in the form of an RC network or a DAC controllable to output a selected voltage shape. The waveform shape required is determined by the LRC network (L 1 , C 1 , C 2 ) around the speaker  112 , and is designed to avoid or attenuate speaker  112  cone movement through limiting the flow transient currents through the speaker  112 . 
     Now referring primarily to  FIG. 2 , an alternative embodiment of the invention is shown in a circuit  200  in which, as described above, the bridge configuration used is a single-ended half-H bridge arrangement  202  that has an output node  204  and a feedback node  206  connected to the respective terminals  208 ,  210 , of a load element, e.g., speaker  212 . In this example, the analog modulator  214  is also provided with gate drives  216 ,  218  connected to the bridge output node  204  using diodes  220 ,  222  in an arrangement adapted for driving the speaker  212 . The op amp  224  is provided for bringing the terminals  208 ,  210  of the speaker  212  to a selected, e.g., mid-rail, voltage level (e.g., 15V) by a different path, however. When the circuit  200  is powered up from an “off” state, the op amp  224  operates to charge the terminal  208 , through the output node  206  of the bridge  202 , to the mid-rail voltage level. Input to the op amp  224  is again preferably provided by a wave-shape circuit block  226 . In this example, the op amp  224  receives its feedback signal from the half-H bridge  202  feedback node  206 . In an alternative configuration, the feedback signal to the op amp  224  may also be taken from the half-H bridge  202  output node  204 . As above, the shape of the waveform of the signal op amp  224  output signal provided at the speaker  212  is controlled by the wave-shape circuit  226 , which can be implemented in the form of an RC network or a DAC controllable to output a selected voltage signal shape. 
     In an exemplary preferred embodiment of the invention portrayed in  FIG. 3 , a circuit  300  is shown in which both the bridge  302  output node  304  and feedback node  306  are brought to a mid-rail voltage level together. This has the advantage of charging all capacitors (e.g., C 1 , C 2 ) without any current flow through the load circuit  312 . The H- bridge  302  output node  304  and feedback node  306  are connected to the terminals  308 ,  310 , of a load  312 . An analog modulator  314  is preferably provided with gate drives  316 ,  318  connected to the output node  304 , using diodes  320 ,  322 , for driving the speaker, or other load element  312 . A first op amp  324  is provided for bringing the bridge feedback node  306  and the corresponding terminal  310  of the speaker  312  to a mid-rail voltage level. The output of the first op amp  324  also serves as the input to a second op amp  325 . The output from the second op amp  325  is coupled with the bridge output  304 , and in turn to the corresponding terminal  308  of the speaker  312 . Thus configured, the circuit  300  is designed to charge the capacitors C 1  and C 2 , while avoiding applying current through the load circuit  312 . The Input to the first op amp  324  is preferably provided by a wave-shape circuit  326 , and this in turn is also the input to the second op amp  325 . The first op amp  324  receives its feedback signal from the bridge  302  feedback node  306 . Alternatively, the feedback signal to the first op amp  324  may also be obtained from the bridge  302  output node  304 . The second op amp  325  receives its feedback signal from the half-H bridge  302  output node  304 , or in the alternative, from the bridge  302  output node  304 . Many variations of the circuit are possible without departure from the invention. For example, the two-amplifier approach having a master amplifier and a slave amplifier, as shown in  FIG. 3 , may alternatively be implemented similar to common-mode feedback in fully differential amplifier topologies. 
       FIG. 4  shows an implementation of a pop and click noise reduction circuit  400  using the class-D amplifier directly to bring up the mid-rail voltage. This preferred embodiment is similar to the circuit introduced in  FIG. 2 , with the distinction that the class-D amplifier is used to apply a noise reduction signal to the load instead of the op amp ( 224 ,  FIG. 2 ). A single-ended half-H bridge  402  has an output node  404  and a feedback node  406  connected to the respective terminals  408 ,  410 , of a speaker  412 . A full bridge may also be used, as may another type of load element. As in the other exemplary circuits herein, an analog modulator  414  is provided with gate drives  416 ,  418  connected to the bridge output node  404  using diodes  420 ,  422  in an arrangement adapted for driving the load element(s)  412 . Equivalent circuits may also be used. A selector circuit  425 , such as a MUX, is provided between an associated system (not shown) that supplies an external signal, and a wave-shape circuit  426 . The selector circuit  425  is configured for selecting either the external signal, typically an audio signal, or a wave-shape circuit  426  output signal for transmittal to the H-bridge output node  404 . In the absence of an external signal, the selector circuit  425  selects the wave-shape circuit  426  output signal to apply to the bridge output node  404 . Preferably, the signal so provided brings the terminals  408 ,  410  of the load  412  to a selected voltage level, e.g., mid-rail voltage. When the selector circuit  425  detects an external signal, it switches to transmit said external signal to the bridge output node  404 . The shape of the waveform of the signal from the wave-shape circuit  426  may be configured as needed, based on selection of RC network components or using a DAC controllable to output a selected voltage shape, for example. 
     Many variations of the pop and click noise reduction circuitry and related methods shown and described are possible within the scope of the invention. An example of an additional implementation is shown in  FIG. 5 , in which the circuit  500  includes a combination of using a single-ended half-H bridge  502  configuration to bring up one terminal  508  (at bridge output node  504 ) of the load  512 , and a linear op amp  525  to bring up the bridge feedback node  506  connected with the other terminal  510  of the load  512 . As shown, a selector circuit  525  is used to select between an external signal and a signal generated by a wave-shape circuit  526  as in the embodiment shown in and described with respect to  FIG. 4 . In this example, the signal provided by the wave-shape circuit  526  is provided to both the class-D amplifier portion  502  of the circuit  500  and as an input to the op amp  524 . In an alternative arrangement, the output of the op amp  524  may be used to provide the wave-shape circuit  526  output signal to the class-D amplifier  502  in order to minimize offsets, and the output of the class-D may be filtered and provided to the input of the op amp  524 . This and the other embodiments and techniques described and illustrated herein may be used in combination and with fully differential class-D architectures as well. 
     The circuits and techniques of the invention provide one or more advantages including but not limited to, reduction or elimination of pop and click noise in audio circuits. While the invention has been described with reference to certain illustrative embodiments, those described herein are not intended to be construed in a limiting sense. For example, variations or combinations of steps or materials in the embodiments shown and described may be used in particular cases without departure from the invention. All of the aspects of implementations of the pop and click noise reduction techniques described and shown can be combined in various ways. Various modifications and combinations of the illustrative embodiments as well as other advantages and embodiments of the invention will be apparent to persons skilled in the arts upon reference to the drawings, description, and claims.