PDM medium wave transmitter digital pulse width modulator adaptive to DRM and modulation method

Abstract

The invention belongs to the technical field of pulse width modulators, and discloses a PDM medium wave transmitter digital pulse width modulator adaptive to a DRM and a modulation method, the PDM medium wave transmitter digital pulse width modulator comprises a DRM adaptation board, and the DRM adaptation board is provided with a digital audio processing circuit, a power amplification circuit, a power control signal generation circuit and an FPGA. A DRM modulation and decoding module, a DDS, a pulse width modulation wave generator and a power control signal processing module are written into the FPGA, the digital audio processing circuit inputs processed audio to the DRM modulation and decoding module, the DRM modulation and decoding module is connected with the DDS, the DDS inputs an audio signal amplitude value to the pulse width modulation wave generator, and the power control signal processing module is connected with the DDS. The power control signal generation circuit inputs a power control signal to the power control signal processing module in the FPGA and converts the power control signal into a direct current signal, and the pulse width modulation wave generator converts an audio signal amplitude value and the direct current signal into a pulse signal and inputs the pulse signal into the power amplification circuit. The power amplification circuit carries out power amplification on the pulse signal and inputs the pulse signal into the transmitter, and the performance is stable.

Description

Technical Field

[0001] The invention belongs to the technical field of pulse width modulators, and relates to a PDM medium wave transmitter digital pulse width modulator adapted to DRM and a modulation method. Background Art

[0002] PDM (Pulse Width Modulation) medium wave transmitter is a medium wave broadcast transmitter that uses pulse width modulation technology. The modulator mainly converts the audio signal into a pulse signal. The audio signal is a continuously changing analog signal that contains various information about the sound, such as frequency, amplitude, phase, etc. The amplitude of the audio signal reflects the loudness of the sound, while the frequency determines the pitch of the sound. The pulse signal is a discrete digital signal that has the advantages of easy processing and strong anti-interference ability. In the digital broadcasting system, the pulse signal can be efficiently encoded, modulated and demodulated through digital signal processing technology.

[0003] Existing modulators are usually implemented using analog circuits, which require a large number of electronic components and complex circuit boards, which not only increases the size and cost of the equipment, but also makes troubleshooting and maintenance difficult. Summary of the invention

[0004] In view of the shortcomings of the prior art, the purpose of the present invention is to provide a PDM medium wave transmitter digital pulse width modulator and modulation method adapted to DRM, so as to solve the technical problems in the prior art that the existing modulator uses a large number of electronic components and complex circuits to increase the size and cost of the equipment, and increase troubleshooting and maintenance.

[0005] In order to achieve the above object, the present invention adopts the following technical solution: The present invention provides a digital pulse width modulator for a PDM medium wave transmitter adapted to DRM, comprising a digital audio processing circuit, a power amplifier circuit, a power control signal generating circuit, and an FPGA installed on a DRM adapter board; a DRM modulation and decoding module, a DDS, a pulse width modulation wave generator, and a power control signal processing module are written on the FPGA; The digital audio processing circuit inputs the processed audio to the DRM modulation and decoding module, the DRM modulation and decoding module is connected to the DDS, the DDS inputs the audio signal amplitude value to the pulse width modulation wave generator, the power control signal generation circuit inputs the power control signal to the power control signal processing module to convert it into a DC signal, the pulse width modulation wave generator converts the audio signal amplitude value and the power control signal into a pulse signal and inputs it into the power amplifier circuit, the power amplifier circuit amplifies the pulse signal and inputs it into the transmitter.

[0006] Furthermore, the digital audio processing circuit includes an industrial computer and a serial port circuit. A host computer is installed on the industrial computer. The digital audio signal of the industrial computer is input into the serial port circuit through DRM encoding processing of the host computer. The serial port circuit is connected with the modulation and decoding of DRM through a filtering circuit.

[0007] Furthermore, it also includes a serial port module, one end of which is connected to the serial port circuit, and the other end of which is connected to the modulation and decoding of the DRM.

[0008] Furthermore, the power amplifier circuit includes a DC power amplifier circuit, a power transistor amplifier circuit, a pulse signal abnormality detection circuit and a signal amplitude detection circuit; the pulse signal output by the pulse width modulation wave generator is transmitted to the input end of the power transistor amplifier circuit and the pulse signal abnormality detection circuit, the output end of the DC power amplifier circuit and the pulse signal abnormality detection circuit is connected to the input end of the power transistor amplifier circuit, and the signal amplitude detection circuit performs abnormality detection on the pulse signal output by the power transistor amplifier circuit.

[0009] Furthermore, it also includes a digital filter, one end of which is connected to the output end of the pulse width modulation wave generator, and the other end of which is connected to the input end of the power amplifier circuit.

[0010] Furthermore, the pulse width modulation wave generator has a total of 1300 gears, the frequency of the pulse signal output by the pulse width modulation wave generator is 72Khz, and the pulse peak value of the pulse signal output by the pulse width modulation wave generator is 13V.

[0011] Furthermore, the frequency control word of the DDS is an adjustable value set by a host computer.

[0012] Furthermore, the baud rate of the serial port of the host computer is 115200 Bd, and there is one stop bit.

[0013] The present invention also provides a digital pulse width modulation method for a PDM medium wave transmitter adapted to DRM. Based on the above-mentioned digital pulse width modulator for the PDM medium wave transmitter adapted to DRM, the method comprises the following steps: a digital audio processing circuit sequentially inputs a digital audio signal into a DRM modulation and decoding module and a DDS through DRM encoding processing of an upper computer; the DDS inputs an amplitude value of the digital audio signal into a pulse width modulation wave generator; a power control signal generating circuit inputs a power control signal into a power control signal processing module to output a direct current signal; the pulse width modulation wave generator converts the amplitude value of the audio signal and the direct current signal into a pulse signal and inputs the pulse signal into a power amplifier circuit; the power amplifier circuit amplifies the power of the pulse signal and inputs the pulse signal into the transmitter.

[0014] Furthermore, the pulse signal abnormality detection circuit in the power amplifier circuit performs abnormality detection on the pulse signal output by the pulse width modulation wave generator. If no pulse signal is detected, the DC power amplifier circuit and the power transistor amplifier circuit are turned off.

[0015] Compared with the prior art, the present invention has the following beneficial technical effects: The present invention discloses a digital pulse width modulator for a PDM medium wave transmitter adapted to DRM. FPGA integrates multiple functions (such as counters, comparators, triggers, etc.) that originally require independent devices to implement into one chip, which significantly reduces the number of components required for the system, thereby reducing the complexity and cost of the system.

[0016] The invention discloses a digital pulse width modulator for a PDM medium wave transmitter adapted to DRM. A pulse width modulation wave generator designed with an FPGA programmable gate array and an internal trigger and a lookup table replaces a plurality of classified devices used in an existing pulse width modulator. The invention has high integration and deep digitization, and ensures stability and reliability during operation.

[0017] The invention discloses a digital pulse width modulator for a PDM medium wave transmitter adapted to DRM. The digital audio processing circuit adopts a combination of an industrial computer and a host computer to input an audio signal into a DRM adapter board through a serial port module. Compared with the existing audio input circuit, the invention has better interface display and controllability and is easy for operators to operate.

[0018] The invention discloses a digital pulse width modulator for a PDM medium wave transmitter adapted to DRM. FPGA receives serial port information and combines a digital audio signal with a power control signal according to a set SPWM algorithm, converts the signal into a duty cycle value, and controls a pulse width modulation wave generator to generate a corresponding duty cycle pulse signal. Compared with the existing analog pulse width modulator, the modulation linearity is higher, the performance is stable, and the signal is not affected by the problems of discrete component aging, temperature drift, etc.

[0019] The invention discloses a digital pulse width modulator for a PDM medium wave transmitter adapted to DRM, which adopts a hardware logic language and has a simple circuit structure, easy function expansion and easy parameter modification. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 The present invention is a structural diagram of a digital pulse width modulator of a PDM medium wave transmitter adapted to DRM; Figure 2 is a structural diagram of a digital audio processing circuit in an embodiment of the present invention; Figure 3 is a structural diagram of a power amplifier circuit in an embodiment of the present invention; Figure 4 4 is a structural diagram of a power control signal generating circuit in an embodiment of the present invention. DETAILED DESCRIPTION

[0021] In order to enable those skilled in the art to better understand the scheme of the present invention, the technical scheme in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work should fall within the scope of protection of the present invention.

[0022] Example 1 The present invention discloses a digital pulse width modulator for a PDM medium wave transmitter adapted to DRM, comprising a DRM adapter board, a digital audio processing circuit, a power amplifier circuit, a power control signal generating circuit, an FPGA, a DRM modulation and decoding module written on the FPGA, a DDS, a pulse width modulation wave generator, and a power control signal processing module. Figure 1 shown.

[0023] like Figure 2 As shown, the digital audio processing circuit includes an industrial computer, a host computer and a serial port circuit connected in sequence. The industrial computer generates a digital audio signal which is processed by DRM encoding of the host computer, and the encoded serial port signal is input to the serial port circuit, and the serial port circuit inputs the digital audio signal to the FPGA.

[0024] The baud rate of the host computer's serial port is 115200, and there is a stop bit. The baud rate determines the speed of data transmission. When the baud rate is set higher, the data transmission speed is faster. The stop bit provides the computer with an opportunity to correct clock synchronization to ensure that the receiving end can correctly identify the end of the data packet.

[0025] The encoding processing process of the upper computer is as follows: first read the audio file, then encode the audio file, call the AAC encoder interface for encoding, encapsulate the encoded data according to the data format of MSC, read the fixed-length audio data from the encoded data to form an audio frame, and then encapsulate the audio frame into an audio superframe. In the process of encapsulating the audio frame into an audio superframe, generate FAC and SDC data according to the requirements of the DRM manual, and finally send the FAC, MSC, and SDC data to the DRM adapter board in the FPGA through the serial port according to the fixed length.

[0026] Specifically, the host computer first needs to read the audio file to be processed from the storage medium (such as hard disk, USB flash drive, etc.). After reading the audio file, the host computer needs to call the AAC encoder interface to encode the audio file. AAC (Advanced Audio Coding) is an efficient audio compression format that occupies less storage space. During the encoding process, the host computer will convert the audio file into AAC format encoded data.

[0027] The encoded data needs to be encapsulated according to the MSC data format and organized into a specific data packet or frame structure. During the encapsulation process, the host computer reads audio data of a fixed length from the encoded data to form an audio frame, which is the basic unit for subsequent processing.

[0028] The audio frame is further encapsulated into an audio superframe. An audio superframe usually contains multiple audio frames and possible other additional information (such as synchronization information, error detection information, etc.). In the process of encapsulating the audio frame into an audio superframe, it is necessary to generate FAC (frame alignment code) and SDC (service description channel) data in accordance with the requirements of the DRM (digital broadcasting technology) manual.

[0029] These data are used for synchronization, error detection and description of service information. Finally, the host computer needs to send the data of FAC, MSC and SDC to the DRM adapter board in FPGA (field programmable gate array) through the serial port according to the fixed length. During the transmission process, the host computer will organize the data into a format that conforms to the serial communication protocol (such as baud rate, data bit, stop bit, etc.) and send it to the DRM adapter board through the serial port. After receiving the data, the DRM adapter board will further process and decode it to restore the original audio signal or perform other processing to pass it to DDS.

[0030] DDS transmits the audio signal amplitude value in the digital audio signal to the pulse width modulation wave generator, where the pulse width modulation wave generator has a total of 1300 gears, the generated pulse wave frequency is 72Khz, and the pulse peak is 13V. The frequency control word of DDS can be adjusted to be set by the host computer.

[0031] Pulse Width Modulation (PWM) is used to approximate analog output by outputting pulses of fixed frequency and different widths to obtain a smoothly changing average voltage. In PWM, the duty cycle refers to the percentage of the time that the pulse is at a higher voltage in the entire pulse cycle. By changing the duty cycle, the pulse width can be adjusted to simulate different output voltage values.

[0032] The PWM wave generator has 1300 gears, and you can select the required pulse waveform parameters, such as pulse width, frequency, etc., from these 1300 different settings. The generated pulse wave frequency is 72Khz. The pulse wave frequency is the number of pulse signals per unit time, which determines the speed of the pulse waveform. 72,000 pulse signals will be generated per second. The pulse peak value is 13V. The pulse peak value is the maximum voltage value in the pulse waveform, which determines the amplitude of the pulse waveform, indicating that the maximum voltage of the pulse waveform is 13 volts.

[0033] The digital audio processing circuit inputs the processed audio to the DRM modulation and decoding module, the DRM modulation and decoding module is connected to the DDS, the DDS inputs the audio signal amplitude value to the pulse width modulation wave generator, the power control signal generation circuit inputs the power control signal to the power control signal processing module to convert it into a DC signal, the pulse width modulation wave generator converts the audio signal amplitude value and the DC signal into a pulse signal and inputs it into the power amplifier circuit, the power amplifier circuit amplifies the pulse signal and inputs it into the transmitter.

[0034] In summary, the digital pulse width modulator of the PDM medium wave transmitter adapted to DRM includes a digital audio processing circuit, a power amplifier circuit, a power control signal generating circuit, an FPGA, and a DRM adapter board; the FPGA integrates a power control signal processing module, a DDS, a DRM modulation and decoding module, and a pulse width modulation wave generator; the output end of the digital audio processing circuit is connected to the DRM modulation and decoding module; the digital audio signal is transmitted to the pulse width modulation wave generator through the DDS, the output end of the power control signal generating circuit is connected to one end of the power control signal processing module, the other end of the power control signal processing module is connected to the pulse width modulation wave generator, and the output end of the pulse width modulation wave generator is connected to the power amplifier circuit.

[0035] It should be noted that the output end of the power amplifier circuit is connected to the pulse amplitude detection circuit; the digital audio processing circuit generates a digital audio signal through the industrial computer and the host computer, and the power control signal generation circuit generates a power control signal. After receiving the digital audio signal from the industrial computer, the serial port module in the FPGA converts it into a digital audio amplitude signal after specific encoding. The power control signal generation circuit generates a power control signal and sends it to the FPGA to obtain the corresponding digital power control signal after preset. The two digital signals are processed and combined through the setting algorithm of the pulse width modulation wave generator, and the duty cycle value is converted to generate a corresponding duty cycle pulse signal; the power amplifier circuit amplifies the signal and outputs it to the outside.

[0036] A serial port module is installed between the digital audio processing circuit and the DRM modulation and decoding module. One end of the serial port module is connected to the digital audio processing circuit, and the other end is connected to the DRM modulation and decoding module. A digital filter is installed between the pulse width modulation wave generator and the power amplifier circuit. One end of the digital filter is connected to the pulse width modulation wave generator, and the other end is connected to the input end of the power amplifier circuit. The digital filter filters the pulse signal that is not within the range to reduce the proportion of the interference signal in the useful signal, thereby obtaining the desired signal characteristics.

[0037] like Figure 3As shown, the power amplifier circuit includes a power triode amplifier circuit, a pulse signal abnormality detection circuit, a signal amplitude detection circuit and a DC power supply amplifier circuit. The pulse signal output by the pulse width modulation wave generator is transmitted to the power triode amplifier circuit and the input end of the pulse signal abnormality detection circuit. The output ends of the DC power supply amplifier circuit and the pulse signal abnormality detection circuit are connected to the input end of the power triode amplifier circuit. The signal amplitude detection circuit performs abnormality detection on the pulse signal output by the power triode amplifier circuit.

[0038] The power transistor amplifier circuit amplifies the pulse signal generated by the pulse width modulation wave generator and outputs it to the outside; the pulse signal abnormality detection circuit detects abnormalities in the input pulse signal, and if there is no pulse signal input, the power transistor amplifier circuit is turned off; the signal amplitude detection circuit detects the amplitude of the pulse signal after the power transistor amplifier circuit, and reports an error when it is detected that the pulse signal amplitude is less than 13V.

[0039] like Figure 4 As shown, the power control signal generating circuit includes a power control manual / automatic switching switch, a power control signal manual controller, a power control signal automatic controller, and a digital control signal processing circuit. The power control manual switching switch is connected to the power control signal manual controller, and the power control automatic switching switch is connected to the power control signal automatic controller. The power control signal manual controller is used to control the generation of manual control signals, and the power control signal automatic controller is used to control the generation of automatic control signals. Both the power control signal manual controller and the power control signal automatic controller are connected to the digital control signal processing circuit. The power control function is realized by changing the algorithm in the FPGA through the power control manual / automatic switching switch.

[0040] The present invention converts the digital audio signal and the power control signal into a duty cycle wallpaper ranging from 0 to 1300, and the specific process is as follows: Calculate the duty cycle when there is no audio input based on the power control signal:

[0041]

[0042] in, To calculate the DC signal value corresponding to the non-audio rated power of the adapted transmitter, is the peak value of the triangle wave in the comparator, and its value is 5336.

[0043] The duty cycle value when there is audio input is calculated based on the active power control signal: :

[0044] in, is the amplitude value of the digital audio signal, The peak value of the triangle wave in the comparator is 5336.

[0045] The calculation methods of the periods of triangular waves and sine waves are different. The frequency calculation of the output pulse is related to the frequency of the triangular wave. The frequency calculation formula of the output pulse is:

[0046] in, is the system clock frequency, and N is the sampling point in a triangle wave.

[0047] Example 2 The invention discloses a digital pulse width modulation method for a PDM medium wave transmitter adapted to DRM, comprising the following steps: a digital audio processing circuit sequentially inputs a digital audio signal into a DRM modulation and decoding module and a DDS through DRM coding processing of an upper computer; the DDS inputs an amplitude value of the digital audio signal into a pulse width modulation wave generator; a power control signal generating circuit inputs a power control signal into a power control signal processing module to output a direct current signal; the pulse width modulation wave generator converts the amplitude value of the audio signal and the direct current signal into a pulse signal and inputs the pulse signal into a power amplifier circuit; and the power amplifier circuit amplifies the power of the pulse signal and inputs the pulse signal into a transmitter.

[0048] Specifically, the digital audio signal is received and processed by the host computer, and the host computer performs DRM encoding on the digital audio signal. The encoded digital audio signal is input into the DRM modulation and decoding module, which converts the digital signal into a modulation signal suitable for transmission. At the receiving end, there will be a corresponding decoding module to restore the original digital audio signal. The DDS receives the amplitude value of the digital audio signal processed by the DRM modulation and decoding module and inputs it into the pulse width modulation wave generator. The power control signal generation circuit inputs the power control signal into the pulse width modulation wave generator and converts it into a DC signal. The pulse width modulation wave generator converts the amplitude value of the digital audio signal and the DC signal into a pulse signal. The pulse signal is input into the power amplifier circuit, and the pulse signal is power-amplified. The amplified pulse signal has sufficient power to drive the transmitter.

[0049] In the description of the present application, it should be understood that the terms "center", "longitudinal", "lateral", "up", "down", "front", "back", "left", "right", "top", "bottom", "inside", "outside", "axial", "radial", "circumferential", etc., indicating orientations or positional relationships, are based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as a limitation on the present invention.

[0050] It should be noted that the terms "first", "second", etc. in the specification and claims of the present invention and the above-mentioned drawings are used to distinguish similar objects, and are not necessarily used to describe a specific order or sequence. It should be understood that the data used in this way can be interchanged where appropriate, so that the embodiments of the present invention described herein can be implemented in an order other than those illustrated or described herein. In addition, the terms "including" and "having" and any variations thereof are intended to cover non-exclusive inclusions, for example, a process, method, system, product or device that includes a series of steps or units is not necessarily limited to those steps or units that are clearly listed, but may include other steps or units that are not clearly listed or inherent to these processes, methods, products or devices.

Claims

1. A digital pulse width modulator for a PDM medium wave transmitter adapted to DRM, characterized in that: It includes a digital audio processing circuit, a power amplifier circuit, a power control signal generating circuit, and an FPGA installed on a DRM adapter board; The DRM modulation and decoding module, DDS, pulse width modulation wave generator, and power control signal processing module are written into the FPGA; The digital audio processing circuit inputs the processed audio to the DRM modulation and decoding module, the DRM modulation and decoding module is connected to the DDS, the DDS inputs the audio signal amplitude value to the pulse width modulation wave generator, the power control signal generation circuit inputs the power control signal to the power control signal processing module to convert it into a DC signal, the pulse width modulation wave generator converts the audio signal amplitude value and the power control signal into a pulse signal and inputs it into the power amplifier circuit, the power amplifier circuit amplifies the pulse signal and inputs it into the transmitter.

2. The DRM-adapted PDM medium wave transmitter digital pulse width modulator according to claim 1, characterized in that: The digital audio processing circuit includes an industrial computer and a serial port circuit. A host computer is installed on the industrial computer. The digital audio signal of the industrial computer is input into the serial port circuit through DRM encoding processing of the host computer. The serial port circuit is connected with the modulation and decoding of DRM through a filter circuit.

3. The DRM-adapted PDM medium wave transmitter digital pulse width modulator according to claim 2, characterized in that: It also includes a serial port module, one end of which is connected to the serial port circuit, and the other end is connected to the modulation and decoding of the DRM.

4. The DRM-adapted PDM medium wave transmitter digital pulse width modulator according to claim 1, characterized in that: The power amplifier circuit includes a DC power amplifier circuit, a power transistor amplifier circuit, a pulse signal abnormality detection circuit and a signal amplitude detection circuit; The pulse signal output by the pulse width modulation wave generator is transmitted to the power transistor amplifier circuit and the pulse signal abnormality detection circuit input end, the DC power supply amplifier circuit and the pulse signal abnormality detection circuit output end are connected to the power transistor amplifier circuit input end, and the signal amplitude detection circuit performs abnormality detection on the pulse signal output by the power transistor amplifier circuit.

5. The DRM-adapted PDM medium wave transmitter digital pulse width modulator according to claim 3, characterized in that: It also includes a digital filter, one end of which is connected to the output end of the pulse width modulation wave generator, and the other end of which is connected to the input end of the power amplifier circuit.

6. The DRM-adapted PDM medium wave transmitter digital pulse width modulator according to claim 2, characterized in that: The pulse width modulation wave generator has a total of 1300 gears, the frequency of the pulse signal output by the pulse width modulation wave generator is 72Khz, and the pulse peak value of the pulse signal output by the pulse width modulation wave generator is 13V.

7. The DRM-adapted PDM medium wave transmitter digital pulse width modulator according to claim 6, characterized in that: The frequency control word of the DDS is an adjustable value set by the host computer.

8. The DRM-adapted PDM medium wave transmitter digital pulse width modulator according to claim 2, characterized in that: The baud rate of the serial port of the host computer is 115200 Bd, and there is one stop bit.

9. A digital pulse width modulation method for a PDM medium wave transmitter adapted to DRM, characterized in that: The DRM-adapted PDM medium wave transmitter digital pulse width modulator according to any one of claims 1 to 8 comprises the following steps: The digital audio processing circuit sequentially inputs the digital audio signal into the DRM modulation and decoding module and DDS through the DRM encoding process of the host computer; DDS inputs the digital audio signal amplitude value into the pulse width modulation wave generator; The power control signal generating circuit inputs the power control signal into the power control signal processing module to output a DC signal; The pulse width modulation wave generator converts the audio signal amplitude value and DC signal into a pulse signal and inputs it into the power amplifier circuit; The power amplifier circuit amplifies the power of the pulse signal and inputs it into the transmitter.

10. The DRM-adapted PDM medium wave transmitter digital pulse width modulation method according to claim 9, characterized in that: The pulse signal abnormality detection circuit in the power amplifier circuit performs abnormality detection on the pulse signal output by the pulse width modulation wave generator. If no pulse signal is detected, the DC power amplifier circuit and the power transistor amplifier circuit are turned off.

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