JP4852800B2 - Wireless transmission device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a wireless transmission device for wirelessly transmitting high-quality audio data using a short-range wireless data transmission system.
[0002]
[Prior art]
There is a standard called Bluetooth as a short-range wireless data transmission system. The current Bluetooth format is primarily intended for voice levels such as telephone calls of 8 kHz sampling called CVSD (Continuous Variable Slope Delta) as a voice transmission system.
[0003]
[Problems to be solved by the invention]
By the way, in the above-described Bluetooth, for example, when audio is transmitted with a high fidelity sound quality of CD (sampling frequency = 44.1 kHz), a multiplying PLL or the like is often used to generate a clock for performing audio signal processing. It is necessary to generate a clock for the audio profile. In addition, in consideration of the Bluetooth baseband clock, an interface circuit and a signal processing circuit unique to the audio profile must be configured. As described above, in the prior art, a clock generation crystal oscillator used in Bluetooth generates a clock for performing audio signal processing with a complicated circuit configuration, which increases power consumption. There is a problem.
[0004]
SUMMARY OF THE INVENTION An object of the present invention is to provide a wireless transmission device that can easily configure a circuit unique to a profile without being affected by a baseband clock for wireless transmission and without increasing power consumption. And
[0005]
In order to solve the above problems, a wireless transmission device of the present invention includes a first signal processing unit that performs signal processing for wirelessly transmitting data, and an RF that is connected to the first signal processing unit and performs wireless communication. A transmission / reception unit; a first crystal oscillator for generating a first clock for wireless transmission used by the first signal processing unit; and a second signal processing unit for performing signal processing of a digital audio data stream; A second crystal oscillator used by the second signal processing unit to generate a second clock that is a sampling clock of the digital audio data stream that is asynchronous with the first clock; A buffer memory that is a FIFO that is disposed between the signal processing unit and the second signal processing unit and temporarily holds data exchanged between the first signal processing unit and the second signal processing unit Based on the amount of data stored in the buffer memory, the operation clock of the second signal processing unit is controlled to absorb time lag due to asynchronous data exchange between the first signal processing unit and the second signal processing unit. And a monitoring unit.
[0008]
In the present invention, the first clock for wireless transmission used by the first signal processing means for performing signal processing for wirelessly transmitting data is generated by the first crystal oscillator. On the other hand, the second crystal oscillator generates a second clock that is used by second signal processing means for performing signal processing for the application specified in the profile and is asynchronous with the first clock. Therefore, it is possible to easily configure a circuit unique to the profile without being affected by the Bluetooth baseband clock and without increasing the power consumption.
[0009]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
A. Configuration of Embodiment FIG. 1 is a block diagram showing a schematic configuration of a Bluetooth transmission apparatus for transmitting an audio signal according to an embodiment of the present invention. The RF transmission / reception unit 1 transmits / receives a radio signal according to the Bluetooth standard in accordance with a clock CL1 from a clock generation unit 3 to be described later. The baseband control unit 2 controls various signal processing such as communication link control, frequency hopping management, packet retransmission, and error correction in accordance with a clock CL1 from a clock generation unit 3 to be described later. The lowest layer of the transport layer is called a baseband packet, and a CRC is added to the header. The upper layer is an L2CAP packet, and an RTP packet for audio transport is placed on the L2CAP packet. The transport frame of each codec is carried on RTP, and CRC is added to the header of the transport frame. The transport frame of the audio codec rides on the RTP.
[0010]
The clock generation unit 3 uses the crystal oscillator 4 to generate a clock CL1 required for Bluetooth transmission, and supplies the clock CL1 to the RF transmission / reception unit 1 and the baseband control unit 2. Since the baseband control unit requires a frequency of 10 MHz in increments of 1 MHz, the crystal oscillator 4 uses 26 MHz / 13 MHz as a source oscillation frequency for the purpose of generating a basic 1 MHz (= Bt clock). The CPU 5 controls each unit (not shown) of the Bluetooth device, the baseband control unit 2 and the like.
[0011]
The clock generation unit 6 uses the crystal oscillator 7 to generate a clock CL2 required for processing an audio signal and supplies the clock CL2 to the codec DSP & audio IF 8. When an audio signal is handled, a specified sampling frequency Fs is required for digitization. In the case of an audio profile that handles high-quality audio signals, 48 kHz, 44.1 kHz, 32 kHz, etc. are required as the sampling frequency Fs. Actually, for an audio IF such as ADC, DAC, IEC958, etc., the crystal oscillator 7 has a source oscillation frequency (24.576 MHz / 22.5792 MHz) that is 512 times the sampling frequency Fs (48 kHz / 44.1 kHz). And
[0012]
The codec DSP & audio IF 8 uses the clock CL2 from the clock generation unit 6 to expand / compress audio data and encode (A /) an audio signal processing unit (such as a reproduction / recording processing unit) (not shown). Audio signal input / output processing such as D conversion) and decoding (D / A conversion) is performed. In order to decode the compressed audio by the codec DSP & audio IF 8, the audio codec transport frame is read, the compression method is recognized, and the audio codec is decoded. As an audio codec, transmission by a plurality of methods such as SBC, ATRAC3, MP3, etc. is possible in the format.
[0013]
The buffer memory 9 is disposed between the Bluetooth (baseband control unit 2) side that operates on the clock CL1 and the audio (codec DSP & audio IF8) side that operates on the clock CL2, and temporarily holds data to be transmitted and received. Operates as a FIFO. The monitoring unit 10 controls the operation clock of the codec DSP & audio IF 8 according to the amount of data held in the buffer memory 9, and absorbs the time lag due to asynchronous data exchange.
[0014]
B. Operation of Embodiment Next, the operation of the above-described embodiment will be described.
The RF transmission / reception unit 1 transmits / receives a radio signal according to the Bluetooth standard in accordance with a clock CL1 generated by a crystal oscillator 4 having a source oscillation frequency of 26 MHz / 13 MHz. The baseband control unit 2 controls various signal processing such as communication link control, frequency hopping management, packet retransmission, error correction, and the like according to the clock CL1 from the crystal oscillator 4.
[0015]
On the other hand, the codec DSP & audio IF 8 uses the clock CL2 by the crystal oscillator 7 having a source oscillation frequency (24.576 MHz / 22.5792 MHz) 512 times the sampling frequency Fs (48 kHz / 44.1 kHz), Expansion / compression and audio signal encoding / decoding are performed.
[0016]
The monitoring unit 10 controls the operation clock of the codec DSP & audio IF 8 according to the amount of data held in the buffer memory 9, and absorbs the time lag due to asynchronous data exchange.
[0017]
According to the above-described embodiment, when an audio profile is handled, the audio profile can be obtained without being affected by the Bluetooth baseband clock by adopting a Bluetooth transmission device capable of mounting a plurality of crystal resonators having different source oscillation frequencies. Unique interface circuits, signal processing circuits, and the like can be configured. In addition, since it is not necessary to generate a clock for an audio profile by frequently using a multiplication PLL or the like, energy saving (power saving) is achieved.
[0018]
According to the present invention, there is an advantage that a circuit unique to a profile can be easily configured without being affected by a baseband clock for wireless transmission and without increasing power consumption.
[Brief description of the drawings]
FIG. 1 is a block diagram showing a schematic configuration of a Bluetooth transmission apparatus for transmitting an audio signal according to an embodiment of the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... RF transmission / reception part (1st signal processing means), 2 ... Baseband control part (1st signal processing means), 3 ... Clock generation part, 4 ... Crystal oscillator (1st crystal oscillation) Child), 5 ... CPU, 6 ... clock generator, 7 ... crystal oscillator (second crystal oscillator), 8 ... codec DSP & audio IF (second signal processing means), 9 ... buffer Memory (buffer means), 10 ... monitoring unit (monitoring means)

Claims (1)

A first signal processing unit that performs signal processing for wirelessly transmitting data;
An RF transmission / reception unit connected to the first signal processing unit and performing wireless communication;
A first crystal oscillator for generating a first clock for wireless transmission used by the first signal processing unit;
A second signal processing unit for performing signal processing of the digital audio data stream;
A second crystal oscillator used by the second signal processing unit to generate a second clock that is a sampling clock of the digital audio data stream that is asynchronous with the first clock;
Data disposed between the first signal processing unit and the second signal processing unit and temporarily exchanged data between the first signal processing unit and the second signal processing unit A buffer memory that is a FIFO to hold;
Based on the data amount of the buffer memory, the operation clock of the second signal processing unit is controlled, and the time of asynchronous data exchange between the first signal processing unit and the second signal processing unit A monitoring unit that absorbs the deviation
A wireless transmission device comprising:

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