Binary phase shift key modulator

Abstract: A Biphase Shift Keying (BPSK) modulation circuit for a digital data transmission system is capable of preventing occurrence of signal distortion even in phase shifting positions upon a power amplification of a modulation signal by providing a constant envelope characteristic to the modulation signal during the modulation. The BPSK modulation circuit has a clock input (100) receiving a system clock, data generation means (10) connected to receive the system clock for providing random digital data in synchronism with the system clock, data conversion means (20) connected to receive the system clock and an output of the data generation means (10), for providing an in-phase signal component and a quadra-phase signal component in synchronism with the system clock, and modulation means (30) connected to receive both the in-phase and quadra-phase signal components from the data conversion means (20), for providing a phase modulation signal of constant envelope on a given carrier-wave signal for the digital data transmission. The in-phase signal component is processed in double-balanced modulation with the carrier-wave and the quadra-phase signal component is processed in single-balanced modulation with a phase-shifted signal of the carrier-wave.

Description: The present invention relates generally to modulation circuits, and is concerned particularly with Biphase Shift Keying (BPSK) modulation for digital telecommunication systems. A known BPSK modulator together with its transmission circuitry is disclosed in Figure 1 of the accompanying diagrammatic drawings, and comprises a data generator 1 providing a given digital signal, a low-pass filter (LPF) 2 suppressing high-frequency components of the digital signal, and a modulator 3 for modulating in phase the filtered output from the LPF into a carrier-wave signal as shown in Figure 2 of the accompanying diagrammatic drawings, which shows a waveform of the modulated output signal from the modulator 3. This modulated signal is delivered to a band-pass filter (BPF) 4 and then amplified in a C-class power amplifier 5. An antenna (ANT) receives the amplified signal for transmission into the air. This type of BPSK modulator, as shown in Figure 1, adopts a modulation system in which a phase of the carrier-wave (CR) is instantaneously shifted by 0° and 180° in dependence upon the digital signal from the data generator, during modulation of the digital signal to the carrier-wave. Thus, when the carrier-wave (CR) passes through the BPF, there occur phenomena that its amplitude decreases at a given zero-crossing position, as shown by reference symbol A in Figure 2, during the shifting of the carrier-wave by 0° and 180°. This is because the frequency in the zero-crossing position becomes outside a passing frequency band in the BPF. Therefore, in the power amplifier 5, operating at C-class level, adequate amplification of the modulated signal may not be provided at the zero-crossing positions, thereby resulting in distortion of output signals. US 3,699,479 (Thompson) discloses a differentional phase shift keying modulation system comprising data conversion means, connected to receive incoming serial data, for providing an in-phase signal component and a quadra-phase signal component and a modulation means, connected to receive both the in-phase and quadra-phase signal components from the data conversion means, for providing a phase modulation system of constant envelope on a given carrier wave signal for the data transmission. Figure 1 of this citation shows an embodiment incorporating a pulse source which is controlled by digital logic means to supply pulses to a frequency modulator via an up/down counting unit to a ring counter. The up/down counting unit determines the direction of counting under control of the digital logic means and the ring counter outputs are weighted and supplied to balanced modulators via low pass filters. The outputs from the modulators are combined and the resultant fed to an output terminal. Preferred embodiments of the present invention aim to provide a BPSK modulation circuit capable of preventing signal distortion in the vicinity of phase shift upon a power amplification of a modulation signal by providing a constant envelope characteristic to the modulation signal during the BPSK modulation. According to a first aspect of the present invention, there is provided a biphase shift keying (BPSK) modulation circuit for a digital data transmission system, the circuit comprising: a clock input for receiving a system clock; data generation means for providing digital data in synchronism with the system clock; data conversion means, connected to receive the system clock and the digital data from the data generation means to produce both in-phase and quadra-phase signal components from the digital data; and modulation means, for providing a phase modulation signal of constant envelope on a given carrier wave signal for digital data transmission, the circuit being characterised in that the digital data from the data generation means are random digital data from a random data generation means, the data conversion means comprises a shift register connected to receive the system clock and the digital data, for providing in parallel a plurality of digital data sequentially shifted from the digital data of the data generation means in synchronism with the system clock, a first resistance array, connected to receive the parallel digital data from said shift register, for providing an in-phase signal component produced in dependence upon multiplication and adding operations therein, said first resistance array having a plurality of resistors each coupled to corresponding ones of outputs of said shift register, a gate array having a plurality of logic gates, each gate being connected to receive a pair of selected two inputs of said shift register, and a second resistance array connected to receive an output of said gate array, for providing a quadra-phase signal component produced in dependence upon multiplication and adding operations therein, said second resistance array having a plurality of resistors each coupled to corresponding ones of the logic gates of said gate array, and said in-phase signal component is processed by said modulation means in double-balanced modulation with the carrier-wave and said quadra-phase signal component is processed in single-balanced modulation with a phase-shifted signal of the carrier-wave, and said double-balanced modulation signal and said single-balanced modulation signal are added to each other. Preferably, said logic gates each comprise an EXCLUSIVE-OR logic gate. Preferably, said modulation means comprises: a first multiplier connected to receive the in-phase signal component, for providing a double-balanced modulation component on the basis of the carrier-wave; a phase shifter connected to receive the carrier-wave for phase shifting the carrier-wave; a second multiplier connected to receive the quadra-phase signal component, for providing a single-balanced modulation component on the basis of the phased-shifted carrier-wave; and an adder connected to add both the outputs of the first and second multipliers, for producing therefrom a resultant biphase shift keying modulation signal. A BPSK modulation circuit as above may further comprise an amplifier for amplifying the biphase shift keying modulation signal from said modulation means. A BPSK modulation circuit as above may further comprise an antenna device coupled to the amplifier, for transmission of the modulation signal into the air. Preferably, said amplifier is of a C-class operation mode. Preferably, said phase shifter is arranged to perform a 90-degrees phase shifting operation on an input signal. Preferably, each resistance of said first and second resistance arrays is arranged to meet the following relationship: [I(t)] 2 + [Q(t)] 2 = C wherein, I(t) represents the in-phase signal component, Q(t) represents the quadra-phase signal component, and C is a given constant. A BPSK modulation circuit as above may further comprise a carrier-wave generation means connected to said modulation means for providing the carrier-wave. The invention extends to a digital data transmission system provided with a modulation circuit in accordance with the abovementioned aspect. For a better understanding of the invention, and to show how the same may be carried into effect, reference will now be made, by way of example, to Figures 3 and 4 of the accompanying diagrammatic drawings, in which: Figure 3 is a schematic block diagram indicating one example of a preferred embodiment of a BPSK modulation circuit according to the present invention; and Figures 4(a) to 4(t) are waveform and timing diagrams for illustrating examples of stages of operation of the modulation circuit of Figure 3. Referring to Figure 3, the illustrated BPSK modulation circuit has a clock input 100, a data generator circuit 10, a data converter circuit 20, a carrier-wave oscillator 170, a modulation circuit 30, an amplifier 220 in C-class, and an antenna (ANT). The clock input 100 receives a system clock. The data generator 10 is connected to receive the system clock, divide it, and provide therefrom random digital data in synchronism with the system clocks. The data converter 20 is connected to receive the system clock and an output of the data generator 10, and is arranged to provide an in-phase signal component and a quadra-phase signal component in synchronism with the system clock. The in-phase and quadra-phase signal components may be of step waveform. The modulation circuit 30 is connected to receive both the in-phase and quadra-phase signal components from the data converter 20, to provide a phase modulation signal of constant envelope on a given carrier-wave signal for the digital data transmission. The in-phase signal component is processed in double-balanced modulation with the carrier-wave, and the quadra-phase signal component is processed in single-balanced modulation with a phase-shifted signal of the carrier-wave, and both the double-balanced modulation signal and the single-balanced modulation signal are added to each other. The amplifier 220 receives an output of the modulation circuit 30 to amplify the output received therefrom in C-class operation mode. The antenna ANT is coupled to receive the amplified output of the amplifier 220 for irradiation of the transmission signal into the air. The data generator 10 is constructed with a divider 110 receiving the system clock to provide therefrom a divided clock, and a random data generator 120 coupled to receive the divided clock, for providing given random digital data. The data converter 20 includes a shift register 130 connected to receive the system clock and the random digital data, for providing in parallel a plurality of digital data sequentially shifted from the random digital data in synchronism with the system clock, and a first resistance array 140 connected to receive the parallel digital data from the shift register, for providing the in-phase signal component produced in dependence upon multiplication and adding operations therein, wherein the first resistance array 140 has a plurality of resistors each coupled to corresponding ones of outputs of the shift register 130. A gate array 150 has a plurality of logic gates, each gate being connected to receive a pair of selected two outputs of the shift register 130, and a second resistance array 160 is connected to receive an output of the gate array 150, for providing the quadra-phase signal component produced in dependence upon multiplication and adding operations therein, wherein the second resistance array 160 has a plurality of resistors each coupled to corresponding ones of the logic gates of the gate array 150. The first and second resistance arrays 140 and 160 each include a respective series of a plurality of resistors R1-R9 and R10-R14, and the gate array 150 includes a plurality of logic gates G1 to G4. Referring to Figures 4(a) to 4(t), various timing diagrams illustrating examples of every operation stage of the circuit of Figure 3, are indicated. In the drawing of Figures 4(a) to 4(t), (a) shows a system clock, (b) an output waveform of the random data generator 120, (c) a waveform divided from the system clock (a) by the divider 110, and (d) to (k) waveforms provided by a shift operation of the waveform (c) in the shift register 130 in accordance with the system clock (a). Further, (1) shows an in-phase data waveform as an output of the first resistance array 140 which processes adding of the outputs (d) to (k) from the shift register 130, (m) a waveform of EXCLUSIVE-ORing operation of the waveforms (d) and (k), (n) a waveform of EXCLUSIVE-ORing operation of the waveforms (e) and (j), (o) a waveform of EXCLUSIVE-ORing operation of the waveforms (f) and (i), (p) a waveform of EXCLUSIVE-ORing operation of the waveforms (g) and (h), and (q) a quadra-phase data waveform as an output of the second resistance array 160 which processes adding of the outputs (m) to (p) of the EXCLUSIVE-OR gates G1 to G4. Furthermore, (r) shows a waveform multiplied by a carrier-wave of the in-phase waveform (l), (s) a waveform multiplied by an output of the phase shifter 190 which shifts in 90° the phase of the carrier wave, of the quadra-phase data waveform (q), and (t) a modulation output signal resulting from adding of the waveforms (r) and (s). Referring to the above-described construction, an example of operation of the BPSK modulation will be described in further detail, hereinafter. Once a system clock (a) is applied through the clock input 100 to the divider 110 in the data generator section 10, the system clock is divided by a given ratio, as shown in the waveform of Figure 4(c). The random data generator 120 receives an output (c) of the divider to therefrom provide random digital data shown in Figure 4(b). The shift register 130 receives at its clock terminal the system clock (a) and the output (b) of the random data generator 120 to provide therefrom at its output (D0-D7) a series of shifted digital data, as shown in Figures 4(d) - 4(k). Here, the output data (d) in D0 output is a digital signal delayed by one clock period time of the output (b) of the random data generator 120, the output data (e) in D1 output is a digital signal delayed by one clock period time of the Do output data (d), and the output data (f) in D2 output is likewise a digital signal delayed by the same clock period of the D1 output data (e). Other remaining output data (g)-(k) in the D3-D7 output of the shift register 130 are provided likewise by a similar shifting operation from a preceding stage. As a result, the output data in the D7 output is obtained by delaying 8 times the output random data (b) of the random data generator. All of the input/output operation in the shift register 130 is adapted to be synchronized with the system clock (a) from the clock input 100. The first resistance array 140 receives a series of the shifted digital data from the shift register 130, which digital data are multiplied by a corresponding resistance value by means of a corresponding resistor R1 to R8 each coupled to a respective output of the shift register 130 and thereafter are added up altogether to produce therefrom an in-phase signal as shown in Figure 4(l). Further, the gate array 150, coupled to the second resistance array 160, also receives the digital data output from the shift register 130, and then performs an EXCLUSIVE-OR operation to selected two outputs, for example, a pair of D0 and D7, or D1 and D6, of the series of shifted digital data in the outputs D0 and D7. The second resistance array 160 having a series of resistors R10 to R13 receives corresponding outputs (m) to (p) of the gate array 150 to multiply the same outputs each by a corresponding resistance and to produce a resultant quadra-phase signal by adding together all of the multiplied outputs of the respective resistors R10 to R13. Here, assuming that the in-phase signal is represented by I(t) and the quadra-phase signal is represented by Q(t), there should be kept a relation of [I(t)] 2 + [Q(t)] 2 = C, wherein C is a constant, in order to obtain a constant envelope characteristic for a BPSK modulation signal subsequent to a given modulation. Thus, it would be well understood to the worker skilled in the art that such a relation will be easily able to be obtained by arranging the corresponding resistance values or combination thereof in the first and second resistance arrays 140 and 160. The carrier-wave oscillator 170 provides a carrier-wave to the first multiplier 180, which multiplies the carrier-wave by the output (l) of the first resistance array 140 to produce therefrom a double-balanced modulation signal as shown by the waveform of Figure 4(r). Further, the second multiplier 200 receives an output of the phase shifter 190, which output is multiplied by the output (g) of the second resistance array (160) to produce therefrom a single-balanced modulation signal as shown by the waveform of Figure 4(s). Here, the adder 210 adds the output (r) of the first multiplier 180 to the output (s) of the second multiplier 200, to provide thereby a resultant BPSK modulation signal with constant envelope characteristic, as seen by the waveform of Figure 4(t). Hence, the resultant BPSK output signal with constant envelope can be precisely amplified even in C-class operation in the power amplifier 220, without any signal distortion due to undesirable fluctuation of an amplitude level in the vicinity of its phase shifting position. This enables the reception of quality data for a receiving party upon transmission of a BPSK modulation signal in a digital telecommunication system. As is apparent from the foregoing description, the illustrated embodiment of the present invention makes it possible to amplify given digital data with constant and adequate level, even in the phase shifting locations or their vicinity, for example, at zero-crossing positions of a BPSK modulation signal in a digital transmission system, so it improves the transmission efficiency of digital telecommunication owing to reception and transmission of quality data. While the foregoing provides a full and complete disclosure of a preferred embodiment of the present invention, various modifications, alternate constructions and equivalents thereof may be employed without departing from the scope of the invention. Therefore, the above description and illustration should not be construed as limiting the scope of the invention, which is defined by the appended claims.

Claims: A biphase shift keying (BPSK) modulation circuit for a digital data transmission system, the circuit comprising: a clock input (100) for receiving a system clock; data generation means (10) for providing digital data in synchronism with the system clock; data conversion means (20), connected to receive the system clock and the digital data from the data generation means (10) to produce both in-phase and quadra-phase signal components from the digital data; and modulation means (30), for providing a phase modulation signal of constant envelope on a given carrier wave signal for digital data transmission, the circuit being characterised in that the digital data from the data generation means (10) are random digital data from a random data generation means (120), the data conversion means (20) comprises a shift register (130) connected to receive the system clock and the digital data, for providing in parallel a plurality of digital data sequentially shifted from the digital data of the data generation means in synchronism with the system clock, a first resistance array (140), connected to receive the parallel digital data from said shift register (130), for providing an in-phase signal component produced in dependence upon multiplication and adding operations therein, said first resistance array (140) having a plurality of resistors (R1-R8) each coupled to corresponding ones of outputs (D0-D7) of said shift register (130), a gate array (150) having a plurality of logic gates (G1-G4), each gate being connected to receive a pair of selected two inputs of said shift register (130), and a second resistance array (160) connected to receive an output of said gate array (150), for providing a quadra-phase signal component produced in dependence upon multiplication and adding operations therein, said second resistance array (160) having a plurality of resistors (R10-R13) each coupled to corresponding ones of the logic gates (G1-G4) of said gate array (150), and said in-phase signal component is processed by said modulation means (30) in double-balanced modulation with the carrier-wave and said quadra-phase signal component is processed in single-balanced modulation with a phase-shifted signal of the carrier-wave, and said double-balanced modulation signal and said single-balanced modulation signal are added to each other. A BPSK modulation circuit according to claim 1, wherein said logic gates (G1 - G4) each comprise an EXCLUSIVE-OR logic gate. A BPSK modulation circuit according to any of claims 1 and 2, wherein said modulation means (30) comprises: a first multiplier (180) connected to receive the in-phase signal component, for providing a double-balanced modulation component on the basis of the carrier-wave; a phase shifter (190) connected to receive the carrier-wave for phase shifting the carrier-wave; a second multiplier (200) connected to receive the quadra-phase signal component, for providing a single-balanced modulation component on the basis of the phased-shifted carrier-wave; and an adder (210) connected to add both the outputs of the first and second multipliers (180,200), for producing therefrom a resultant biphase shift keying modulation signal. A BPSK modulation circuit according to any of the preceding claims, further comprising an amplifier (220) for amplifying the biphase shift keying modulation signal from said modulation means (30). A BPSK modulation circuit according to claim 4, further comprising an antenna device (ANT) coupled to the amplifier (220), for transmission of the modulation signal into the air. A BPSK modulation circuit according to claim 4 or 5, wherein said amplifier (220) is of a C-class operation mode. A BPSK modulation circuit according to claim 3 or to claim 3 together with any of claims 4 to 6, wherein said phase shifter (190) is arranged to perform a 90-degrees phase shifting operation on an input signal. A BPSK modulation circuit according to claim 2 or to claim 2 together with any of claims 3 to 7, wherein each resistance of said first and second resistance arrays (140, 160) is arranged to meet the following relationship: [I(t)] 2 + [Q(t)] 2 = C wherein, I(t) represents the in-phase signal component, Q(t) represents the quadra-phase signal component, and C is a given constant. A BPSK modulation circuit according to any of the preceding claims, further comprising a carrier-wave generation means (170) connected to said modulation means (30) for providing the carrier-wave.

Inventors: CHEON BYOUNG-JIN, CHEON, BYOUNG-JIN
Applicants: SAMSUNG ELECTRONICS CO LTD, SAMSUNG ELECTRONICS CO., LTD.
Application year: 1991
Main classification: H04L27
IPC codes: H04L27, H03C3, H03K7