Digital stereo multiplexing-demultiplexing system based on linear processing of a Delta - Sigma modulated bit-stream

Abstract

Disclosed is a digital stereo multiplexing-demultiplexing system based on the use of delta-sigma modulation. Creation of left (LR) and right (L+R) channels is achieved using a binary delta adder IC circuit. Delta adder is an ordinary binary adder with an interchanged role of the Sum and Carry-Out terminals. Two channel multiplexer and demultiplexer are implemented with ordinary binary logic gates. Output of the multiplexer is modulated and transmitted to the receiver where demultiplexing is performed. The proposed method can combine two or more digital stereo channels. This method is not application limited, and can be used in acoustic, video, or photo applications.

Claims

1. A digital stereo multiplexing apparatus comprising: a two transducer; a two second-order or higher-order delta-sigma modulator; an inverter; a two-delta adder; a binary address A; a two-channel multiplexer; and a radio-frequency transmitter.

2. A digital stereo demultiplexing apparatus comprising: a radio-frequency receiver; a two-channel demultiplexer; a binary address A; an inverter; a two-delta adder; a two low-pass filter; and a two transducer.

3. A delta-sigma modulation digital processing system on chip (SoC) comprising: a left (L) and right (R) delta-sigma modulated channels; a two-delta adder with an inverter; a two-channel multiplexer with an output Z, an inverter, and a binary address A; a two-channel demultiplexer with an inverter and a binary address A; and a two-delta adder with an inverter and an output delta-modulated bit-streams L and R.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0032] FIG. 1 shows a block diagram of the FM stereo system (Prior Art).

[0033] FIG. 2 shows a block diagram of a binary delta adder (Prior Art).

[0034] FIG. 3 shows the proposed digital stereo multiplexing-demultiplexing system.

[0035] FIG. 4 shows input-output waveforms for identical input signals MK1 and MK2.

[0036] FIG. 5 shows input-output waveforms for two different signals of MK1 and MK2.

[0037] FIG. 6 shows a block diagram of the proposed integrated circuit (IC) chip.

DETAILED DESCRIPTION OF THE INVENTION

Definition

[0038] A stereo multiplexing-demultiplexing system is the main component of any stereo transmission system. Most existing stereo techniques are based on a frequency multiplexing technique. The proposed method of this invention consists of a high resolution - modulator whose resolution is greater than 20 bits. In addition to the simple and inexpensive high-resolution - modulator implementation [3], [4], it is possible to perform linear arithmetic operations of addition, subtraction, and multiplication by a constant less than 1 on its bit-stream. To implement addition/subtraction of the left (L) and right (R) channels a special circuit must be developed. An ordinary serial binary adder, with interchanged role of the terminals of Carry-Out and Sum, can perform addition/subtraction of two - modulated bit-streams [2]. Thus, the main contribution of this invention is a simple, inexpensive and reliable digital stereo multiplexing-demultiplexing system, based on a direct arithmetic operation on a - modulated bit-stream.

The Best Mode of Invention

[0039] The block diagram of the proposed method, with supporting simulation results, is presented. Herein the best mode contemplated by the inventor shell be presented.

How to Make the Invention

[0040] As can be seen from FIG. 3 the proposed system consists of a number of distinct components. Thus, it is necessary to describe every component separately.

[0041] FIG. 3 shows a block a diagram of a proposed stereo transmitter (Tx) and receiver (Rx). Even though any type of higher order - modulator can be employed as ADC in our simulation model, a second-order - modulator is used. Without loss of generality, instead of a microphone (MK1 and MK2), different transducers can be used such as a photo camera, recorded CD or taped music. For example, a transducer can be integrated with a - modulator to implement a digital mike or stereo sensing system for robotic applications. - modulators (1 and 2) are highly oversampled where sampling frequency is much higher than a frequency of an input signal (F.sub.sampling>>2F.sub.B, where 2F.sub.B is Nyquist sampling frequency). Depending on the application the oversampling factor R can vary (R=F.sub.samp./2F.sub.B). - modulated bit-streams, L and R, are added in a delta adder A2 (4) to produce a binary bit-stream L+R. To produce a bit-stream LR, the R bit-stream must be first inverted (5) and added to a bit stream L in A1 (3). The block diagram of a binary A is shown in FIG. 2 (Prior Art) as an ordinary serial binary adder with interchanged roles of Sum and Carry-Out terminals. According to Kouvaras [2] the Sum of two delta modulated bit-streams is defined as

Sn=[Ln+Rn]+error(1)

The error signal consists of both quantization noise and Carry-Out propagation noise. This error can be minimized with proper design (higher order modulator) and increase of a sampling frequency. One can see that a A introduces an attenuation of one half. Depending on a sign of Carry-Out of delta adder, Ln and Rn have always the same sign. Thus, Sn is always +1 or 1 [2]. If needed, one can overcome this attenuation by amplification at a receiver. - modulated bit-streams LR and L+R are multiplexed using 2 channel multiplexers (6) with binary address A. The output Z of multiplexer is given by Boolean expression

Z=*(LR)+A*(L+R)

If A=1 L+R bit-stream is passed to the RF modulator (7), and if A=0 (=1) then the LR bit-stream is modulated in (7). Depending on the application, a digital bit-stream can be modulated using different types of modulation such as FM, AM, ASK, etc. Radio signals can occupy different frequency bandwidths, licensed or unlicensed. Thus, a proposed stereo digital apparatus is not application limited.

[0042] Stereo receiving system Rx, shown in FIG. 3, consists of a standard RF receiver (15) and (16) to produce a signal Z. Digital bit-stream Z is fed into a demultiplexer whose outputs are given by Boolean expression

*Z=*[*(LR)+A*(L+R)]=*(LR), and

A*Z=A*[*(LR)+A*(L+R)]=A*(L+R)

One can see if A=1 then L+R is passed to both A1 (10) and A2 (13). Inverting *Z in (12) one gets L+R. Thus, output of A2 (13) is L+RL+R=2R. Similarly, output of A1 is 2L when A=0. It is important to remember that a delta adder performs algebraic operations (not Boolean) on a delta-sigma bit stream. Inversion means change of sign of binary signal (+1 to 1 or 1 to +1).

[0043] In FIG. 4 simulation results are shown when both sound signals are identical (frequency and amplitude of mikes signals, MK1 and MK2, are identical). It is shown that received signals, SPK1 and SPK2, are identical (they are inverted for clarity reasons). According to equation (1) A introduces attenuation of at the transmitting site. Similarly, A introduces attenuation of at the receiver. Thus, the total channel attenuation is . During the demultiplexing process delta adder adds two identical signals, thus overall channel attenuation is . However, demodulating LPF (11) and (14) introduce additional attenuation which depends on the order of a filter and its cut-off frequency.

[0044] FIG. 5 shows an example of two input signals (MK1, MK2) of two different frequencies (F.sub.MK1=2F.sub.MK2). Again, one can see correctly demodulated waveforms SPK1 and SPK2. If needed received signals SPK1 and SPK2 can be amplified.

[0045] FIG. 6 shows an IC chip, which consists of the following digital circuits: 4 delta adders, 4 inverters, 2-channel multiplexer and 2-channel demultiplexer. Depending on the application, one can envision different scenarios of integration. One possibility is shown if FIG. 6. The proposed IC system can be integrated with a delta-sigma modulator and transducer as well to implement a system on chip (SoC). Another option is in multiplexing 4 or more channels. Yet another possibility is to multiplex output Z with identical output of a second IC chip. Even though digital multiplexing technique is well established in many areas of engineering and science, there is still space for originality. It is obvious that a possibility of direct processing of a delta-modulated bit-stream leads to a novel solution of a system-on-chip (SoC) shown in FIG. 6. It is also obvious that a delta-sigma multiplexed bit-stream (signal Z), can be modulated in many different ways (put on RF carrier), and transmitted wirelessly, or over other transmission media. It is not obvious that prior art solutions could lead to the claims at issue in this application.

How to Use the Invention

[0046] Stereo is a method of sound reproduction that creates an illusion of multidirectional audible perception. Using two or more independent channels connected with two or more loudspeakers can create the impression of sound coming from various directions as in natural hearing. Stereo sound is common in entertainment systems such as broadcast radio, TV, cinema or recorded music. In addition, stereo photography is a method to produce stereoscopic images, videos, or films. This is usually achieved using specially built stereo cameras, paired or single. In stereo photography the goal is to duplicate natural human vision. Stereo techniques could be used to help pilots fly planes, to help a ground-based crew to fly drones, and to navigate unmanned vehicles or robots. Regardless of what kind of stereo application one choses, the correct baseline (distance between left and right mike, or camera, or where two images are taken) is of critical importance. However, selection of the correct baseline does not help if a high-resolution digital transducer (mike or camera) does not exist. The proposed method of digital stereo multiplexing uses a high-resolution delta-sigma modulator (resolution greater than 20 bits) as the analog-to-digital converter. Its use can be found in acoustic and video applications. A novel method of stereo multiplexing and creation of left and right digital channels is based on non-conventional digital signal processing using a delta adder. It is apparent to one familiar with the art of non-conventional signal processing that a digital stereo signal Z can be combined (multiplexed) serving different purposes.