The patent's assignee is
News editors obtained the following quote from the background information supplied by the inventors: "The present invention relates to the amplification of differential audio signals, such as those produced by high-quality microphones.
"Differential signaling is a commonly-used technique for transmitting information, whereby two complementary but opposite signals are sent on two separate, and typically balanced, transmission lines--possibly in a single cable. The motivation for employing differential signaling is invariably due to the need to suppress the effect of noise on the cabling used to transmit the information. For instance, even though the level of a signal transmitted over a cable may be reasonably large, say of the order of 100 millivolts, the length of the cable itself may cause the introduction of a significant degree of noise into both lines--in some cases up to ten volts of noise. By transmitting information in differential mode, where the signals are of opposite polarity to one another, the noise will however manifest as a common-mode signal.
"The standard approach to recovering the original signal is to subtract the two signals on each line from one another in a pre-amplification stage, thereby rejecting the common-mode noise present on the two lines. Such an approach is commonly taken in high-quality microphone pre-amplifiers, particularly in mixing consoles of the known type, which pre-amplifiers also provide controllable gain.
"Problems exist, however, with this approach to recovering the differential signal whilst maintaining common-mode rejection. Due to the inherent topology of circuits presently used in microphone amplifiers, there is no concept of electrical ground at the point in the circuit where gain is controlled. The introduction of variable gain elements that require a connection to ground, such as a digital-to-analog converter (DAC), is therefore not possible. Thus, up until now it has not been feasible to employ commodity DACs in differential signal amplifiers to allow digitally controllable gain."
As a supplement to the background information on this patent application, VerticalNews correspondents also obtained the inventor's summary information for this patent application: "According to an aspect of the present invention, there is provided An amplifier for amplifying a differential audio signal having two complimentary parts, said amplifier having common-mode rejection and digital gain control, and comprising: a first current source configured to supply a constant level of current to a first current path, and a second current source configured to supply a constant level of current to a second current path; an input stage configured to modulate the current in said first current path and said second current path in response to a differential input signal, thereby producing an amplified differential signal defined by the difference in currents in said first current path and said second current path; an output stage configured to produce an output signal by amplifying said amplified differential signal; a feedback stage configured to modulate the current in said first current path by said output signal and to modulate the current in said second current path by the inverse of said output signal, so as to provide a degree of feedback to said input stage; wherein the degree of modulation by said feedback stage is determined by the attenuation provided by at least one multiplying digital-to-analog converter located therein.
"According to further aspect of the present invention, there is provided a method of controlling the gain applied during amplification to a differential audio signal having two complementary parts, said method comprising steps of: (i) supplying a constant level of current to a first current path and a second current path; (ii) controlling the current in said first current path in response to the first part of said differential audio signal, and controlling the current in said second current path in response to the second part of said differential audio signal; (iii) amplifying the difference between the currents in said first current path and said second current path to produce an output signal; (iv) generating a first feedback control signal by attenuating said output signal, and generating a second feedback control signal by inverting and attenuating said output signal; (v) generating a degree of feedback by controlling the current in said first current path in response to said first feedback control signal and controlling the current in said second current path in response to said second feedback control signal; wherein the degree of attenuation applied during step (iv) is determined by the attenuation provided by at least one multiplying digital-to-analog converter.
BRIEF DESCRIPTION OF THE DRAWINGS
"FIG. 1 shows an example of an environment in which the present invention can be used;
"FIG. 2 shows a schematic representation of an exemplary mixing environment;
"FIG. 3 shows an example of a known approach to providing a pre-amplification stage for a microphone;
"FIG. 4 shows a high-level block diagram of a circuit topology implementing the principles of the present invention;
"FIG. 5 shows a practical approach to achieving the required functionality of the present invention;
"FIG. 6 shows an alternative embodiment based on the circuit illustrated in FIG. 5;
"FIG. 7 shows an approach to implementing digital-to-analog conversion; and
"FIG. 8 shows a dominant-pole compensation circuit used in certain embodiments of the present invention."
For additional information on this patent application, see: Mate,
Keywords for this news article include: Electronics, Digital To Analog,
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