Abstract:
A voltage regulator, comprising an analog amplifier, a noise filter and a signal compensator, is disclosed. The noise filter for receives a first signal containing alternating current (AC) noise in which the noise filter substantially filters the AC noise from the first signal to thereby produce a second signal. The voltage regulator regulates the second signal to thereby generate a third signal therefrom. The third signal is substantially noise-free and is provided as a biasing voltage to the analog amplifier. The first signal is further provided to for amplification by the analog amplifier based on amplification characteristics of the analog amplifier and the amplification characteristics of the analog amplifier is determined by the biasing voltage provided to the analog amplifier.

Description:
FIELD OF INVENTION 
       [0001]    The invention relates generally to electronic amplifier circuits. More specifically, the present invention relates to a voltage regulator for biasing current-to-voltage amplifiers during operation thereof. 
       BACKGROUND 
       [0002]    For high fidelity (Hi-Fi) audio reproduction from digital sources such as audio compact disc (CD), super-audio CD (SACD), DVD-audio (DVDA), and digital audio broadcasts (DAB) using digital audio reproduction equipment, the measured root-means-square (rms) values of analog signals provided by the digital audio reproduction equipment are typically approximately 2 volts. Digital-to-analog converters (DACs) are normally installed in the digital audio reproduction equipment for converting digital audio data retrieved from the digital sources into analog signals. The analog signals provided by modern DACs are either current-based or voltage-based. If the DACs provide current-based analog signals, then conversion of the current-based analog signals into the corresponding voltage equivalent is required before the analog signals are to be further provided to subsequent stage amplifiers. 
         [0003]    A commonly used technique employs a circuit built with operational amplifiers (op-amps) thereon for such current-to-voltage conversion. As known to ordinary persons skilled in the art, the circuit is usually termed trans-impedance amplifier or current-to-voltage (I/V) amplifier. Conventionally, the circuit is configured such that the analog signals provided by the DAC bias the inverting input of the op-amp of the circuit and a voltage output is developed across a feedback resistor that is connected between the output of the op-amp to the inverting input of the op-amp. In such a configuration, the output of the DAC operates with respect to a virtual ground and the non-inverting input of the op-amp operates with respect to a reference ground. In addition, the circuit also operates with enabled negative feedback. 
         [0004]    In general, for excellent Hi-Fi audio reproduction, circuits operating without negative feedback are highly desired to prevent the quality deterioration of the reproduced audio due to negative feedback. In addition, the circuits preferably operate in conformance with the operating characteristics of Class-A amplifiers for achieving low output impedance. Furthermore, operating the circuits to conform to performances of Class-A amplifiers is also essential for ensuring proper operation of the circuits regardless of the voltage characteristics of the power supply being provided to the circuits. Lastly, the absence of feedback loop circulating within the circuits is also desired. Regrettably, existing circuits are however unable to meet at least one of the foregoing criterion required for excellent audio reproduction. 
       SUMMARY 
       [0005]    Embodiments of the invention disclosed herein provide a voltage regulator and a method for biasing current-to-voltage amplifiers in which alternating current (AC) signal feedbacks are substantially eliminated. 
         [0006]    In accordance with a first aspect of the invention, there is disclosed a voltage regulator comprising an analog amplifier, a noise filter and a signal compensator. The noise filter receives a first signal containing alternating current (AC) noise, the noise filter substantially filtering the AC noise from the first signal to thereby produce a second signal. The signal compensator regulates the second signal to thereby generate a third signal therefrom. The third signal is substantially noise-free and is provided as a biasing voltage to the analog amplifier. The first signal is further provided to for amplification by the analog amplifier based on amplification characteristics of the analog amplifier and the amplification characteristics of the analog amplifier is determined by the biasing voltage provided to the analog amplifier. 
         [0007]    In accordance with a second aspect of the invention, there is disclosed a voltage regulating method comprising providing an analog amplifier. Further, the method comprises receiving a first signal containing alternating current (AC) noise by a noise filter, the noise filter substantially filtering the AC noise from the first signal to thereby produce a second signal. Additionally, the method comprises regulating the second signal by a signal compensator to thereby generate a third signal therefrom. The third signal is substantially noise-free and is provided as a biasing voltage to the analog amplifier. The first signal is further provided to for amplification by the analog amplifier based on amplification characteristics of the analog amplifier and the amplification characteristics of the analog amplifier is determined by the biasing voltage provided to the analog amplifier. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]    Embodiments of the invention are disclosed hereinafter with reference to the drawings, in which: 
           [0009]      FIG. 1  shows a block diagram of the different key stages in audio signal amplification; 
           [0010]      FIG. 2  shows a components block diagram representation of a circuit for biasing the current-to-voltage amplifier according to an embodiment of the invention; and 
           [0011]      FIG. 3  shows a circuit diagram representation of the circuit of  FIG. 2 . 
       
    
    
     DETAILED DESCRIPTION 
       [0012]    A voltage regulator and a method for biasing current-to-voltage amplifiers in which alternating current (AC) signal feedbacks are substantially eliminated are described hereinafter for addressing the foregoing problems. 
         [0013]    For purposes of brevity and clarity, the description of the invention is limited hereinafter to applications related to devices for biasing current-to-voltage amplifiers. This does not however preclude various embodiments of the invention from other applications that require similar operating performance. The fundamental operational and functional principles of the embodiments of the invention are common throughout the various embodiments. 
         [0014]    Exemplary embodiments of the invention described hereinafter are in accordance with  FIGS. 1 to 3  of the drawings, in which like elements are numbered with like reference numerals. 
         [0015]      FIG. 1  shows a block diagram of the different key stages in audio signal amplification. A signal provider  102  provides source signals to a digital-to-analog converter (DAC)  104 . The signal provider  102  is preferably a digital audio device such as a CD-player or MP3 player that outputs digital signals. The DAC  104  then converts digital audio data retrieved from the source signals into current-based analog signals. The analog signals typically measure approximately in the range of few milliamperes (mA). Further, the output of the DAC  104  is biased with reference to an analog ground. The analog signals are then provided to an amplifier  106  in which the analog signals undergo signal amplification. Typically, the amplifier  106  is preferably operated in a desired operating region so as to obtain the required amplification characteristics. Based on the amplification characteristics of the amplifier  106 , signal amplification is then performed within the linearity zone of the desired operating region. The amplified signals are then provided to a next-stage device  108  such as a pre-amplifier or a power-amplifier which further boosts the signal strength of the amplified signals for provision to subsequent output devices such as loudspeakers to be transduced into audible signals. 
         [0016]      FIG. 2  shows a components block diagram representation of a voltage regulator  200  according to an embodiment of the invention. The voltage regulator  200  is connected to a current-to-voltage amplifier  202  (hereinafter amplifier). Typically, the amplifier  202  is an analog amplifier and is implemented using a triode. The triode typically comprises three input terminals: an anode, a cathode and a grid. Alternatively, the amplifier  202  is implementable using circuit components such as field effect transistors, bipolar transistors or the like. 
         [0017]    The voltage regulator  200  comprises a voltage reduction module  204 , an AC signal cancellation module  206  and error amplifiers  208 . As shown in  FIG. 2 , the voltage regulator  200  provides two biasing voltages to the amplifier  202 . A current source  209  is connected to the anode of the amplifier  202  for providing low-output impedance. Further, the current source  209  is connected to a voltage source V+that preferably supplies a voltage having a value that exceeds one hundred and fifty volts. Further, the voltage source V +  is also coupled to a first potential divider circuit  212   a . In addition, a reference voltage V ref  is provided to a second potential divider circuit  212   b . The reference voltage V ref  is preferably maintained at substantially half the value of the voltage provided by the voltage source V + . Alternatively, the reference voltage V ref  is maintained at any preset voltage value. The reference voltage V ref  is also referenced from the second potential divider circuit  212   b  to the first potential divider circuit  212   a  by using the “voltage-mirroring” configuration. Hence, the first potential divider circuit  212   a  is also maintained at a voltage having the voltage value of the reference voltage V ref  as well. 
         [0018]    When input signals provided by the voltage source V +  are received by the first potential divider circuit  212   a , the input signals are then provided to a first AC signal cancellation circuit  214   a  for further processing. The first AC signal cancellation circuit  214   a  substantially removes any AC signals present in the input signals. Similarly, reference signals contained in the reference voltage V ref  at the second potential divider circuit  212   b  are also sent to a second AC signal cancellation circuit  214   b  for processing to substantially remove the presence of any AC signals in the reference signals. 
         [0019]    Both the processed input and reference signals are then fed into a first error amplifier  208   a . The first error amplifier  208   a  functions as a signal compensator by comparing an input signal with a reference signal. Voltage differences between the input signal and the reference signal are then compensated for by the first error amplifier  208   a . Hence, the first error amplifier  208   a  provides an output that is substantially free of AC signals to a load component  216  such as a resistor. Additionally, the voltage at the cathode of the amplifier  202  is maintained at approximately zero volts. Further, a biasing current flowing through the load component  216  is constantly regulated at a value approximately equal to the value provided by the current source  209  for optimal performance. 
         [0020]    Due to the need to bias the amplifier  202  at the grid, it is undesirable to re-introduce any AC signals contained in input signals from a source  210  or other sources of noise to (or across) the amplifier  202 . The source  210  is preferably a DAC that provides current-based analog signals. Alternatively, the source  210  is an alternating current (AC) source. Thus, the input signals from the source  210  are first provided to a third AC signal cancellation circuit  214   c . The third AC signal cancellation circuit  214   c  removes any AC signals present in the input signals and minimizes possible re-introduction of AC signals back into the amplifier  202 . The processed signals from the third AC signal cancellation circuit  214   c  are then provided to a second error amplifier  208   b  for compensating voltage differences. The second error amplifier  208   b  is referenced with respect to an analog ground. Notably, output signals from the second error amplifier  208   b  are substantially free of AC signals. Subsequently, the output signals from the second error amplifier  208   b  are then fed to the amplifier  202 . 
         [0021]    A grid resistor  218 , coupled in between the amplifier  202  and the second error amplifier  208   b , receives the output signals and provides a biasing voltage to the amplifier  202 . The biasing voltage determines amplification characteristics of the amplifier  202 . The amplifier  202  then provides output signals at an output  220  in which the output signals are amplified signal equivalents of the input signals based on the amplification characteristics of the amplifier  202 . Furthermore, the output signals are also substantially distortion-free. 
         [0022]      FIG. 3  shows a circuit diagram representation of the voltage regulator  200 . As shown in  FIG. 3 , each of the first potential divider circuit  212   a  and second potential divider circuit  212   b  is constructed from a pair of resistors coupled in series for obtaining a reduced-voltage output across each of the resistors. The first potential divider circuit  212   a  is configured from resistors R 1  and R 2  and the second potential divider circuit  212   b  is configured from resistors R 3  and R 4 . 
         [0023]    The first AC signal cancellation circuit  214   a  and the second AC signal cancellation circuit  214   b  of the AC signal cancellation module  206  are configured using operational amplifiers (op-amps) in combination with other circuit components to form a subtractor-circuit (also known as a differential amplifier). For example, the first AC signal cancellation circuit  214   a  comprises op-amp OA 1 , capacitor C 1  and resistors R 18 , R 19 , R 20  and R 21 . Typically, a primary voltage signal comprising both AC and DC components (V AC+DC ) is provided to the non-inverting terminal of op-amp OA 1 . Separately, the inverting terminal of op-amp OA 1  is provided only with a secondary voltage signal comprising only the AC component (V AC ). Hence, after the op-amp OA 1  processes the primary voltage signal and secondary voltage signal, an output signal comprising only the DC component (VDC) is produced. Separately, the second AC signal cancellation circuit  214   b , comprising op-amp OA 2 , capacitor C 2  and resistors R 14 , R 15 , R 16  and R 17 , operates similarly as the first AC signal cancellation circuit  214   a . In general, op-amps OA 1  and OA 2  each receives an equal proportion of the reduced-voltage output provided by the voltage reduction module  204  as a result of the high voltages provided by the voltage source F + . 
         [0024]    The first error amplifier  208   a  coupled to the AC signal cancellation module  206  is constructed from an op-amp OA 3  that receives the outputs provided by the AC noise cancellation module  206 . Resistors R 5  and R 6  are connected to the non-inverting and inverting terminals of op-amp OA 3  in which resistors R 5  and R 6  are coupled in between the AC noise cancellation module  206  and op-amp OA 3  for reducing the signal magnitude of the inputs received by the first error amplifier  208   a . In addition, capacitor C 3  couples the inverting terminal to the node point of the output of op-amp OA 3 . The output of op-amp OA 3  serves to provide and regulate a biasing voltage to the load component  216 . 
         [0025]    Additionally, the third AC signal cancellation circuit  214   c  has a configuration similar to that of the first AC signal cancellation circuit  214   a  and the second AC signal cancellation circuit  214   b . The third AC signal cancellation circuit  214   c  is configured as a subtractor-circuit comprising op-amp OA 4 , capacitor C 4  and resistors R 10 , R 11 , R 12  and R 13 . 
         [0026]    Finally, the second error amplifier  208   b  comprises an op-amp OA 5  with the inverting terminal being referenced to an electrical ground in which the source  210  is similarly being referenced to. The non-inverting terminal of op-amp OA 5  is then coupled to capacitor C 5 , which in turn is coupled to the output of op-amp OA 5 . The output of op-amp OA 5  is then connected to the grid resistor  218 , which is in turn connected to the grid of the amplifier  202 . Furthermore, a resistor R 7  is coupled to the non-inverting terminal of op-amp OA 5  at a node point before the output from the third AC signal cancellation circuit  214   c  is received by op-amp OA 5 . 
         [0027]    In the foregoing manner, a voltage regulator and a method for biasing current-to-voltage amplifiers in which alternating current (AC) signal feedbacks are substantially eliminated are described according to various embodiments of the invention for addressing the foregoing disadvantages. Although a few embodiments of the invention are disclosed, it will be apparent to one skilled in the art in view of this disclosure that numerous changes and/or modification can be made without departing from the scope and spirit of the invention.