Patent Application
20130058419
1. Technical Field
The present invention relates to a wireless video/audio data transmission system capable of adjusting Phase-Locked Loop (PLL) parameters. More particularly, this invention relates to a wireless video/audio data transmission system able to synchronize the rate of clock reference information transmitted from a video/audio data stream by adjusting the PLL residing in either a decoder or encoder module.
2. Description of Related Art
The increasing demand for digital wireless audio/video data presents an ever increasing problem of effectively controlling data transmission in a wireless audio/video transmitter receiver system. As the volume of audio/video data transmission increases in response to greater demand, it becomes increasingly more difficult to handle the large amount of transmitted audio/video information. Conventionally, the data streams contain video, audio, timing information and control data which are packaged and transmitted as a composite whole. The data, control elements, timing information and other information are arranged in various specific formats according to various standards, such as MPEG-1, MPEG-2, MPEG-4, h.264/AVC and others.
For supporting the requirements for high definition television, a High Definition Multimedia Interface (HDMI) receiver is typically used. HDMI receivers support an input reference clock frequency range of 25 MHz to 165 MHz. HDMI is an audio/video interface capable of transmitting uncompressed streams. Typically HDMI provides an interface between any compatible digital audio/video source, such as a set-top box, a DVD player, a PC, a video game console, or an audio video (AV) receiver and a compatible digital audio and/or video display or monitor, such as a high definition television (HDTV).
An important component of the video/audio data stream is the timing information which is used to synchronize the decoding and presentation of the video and audio data. For example, MPEG defines timing information in terms of timestamps or clock references. The MPEG standards permit an encoder to selectively adjust the transmission rate of timestamps in performing its encoding function. One restriction is that the time interval between timestamps must not exceed a specified range. On the other hand, timing information is essential for proper reproduction of the real-time video/audio data stream transmitted wirelessly.
In the conventional video decoder, such as H.264/AVC video decoder, for example, cache memory for frame buffering is usually provided in the form of an off-chip external DDR memory. Therefore, the DDR memory adds cost and integrated circuit footprint. Typically only fully-processed or decoded pixel data are stored in the DDR, instead of storing frame data in the compressed domain. Video playback is typically at 30 frames per second and at 720 p or 1080 p. Because the frame buffer has a limited memory, thus, only a small number of video frame data can be stored inside the DDR memory.
As described above, the cache buffer or frame buffer needs are typically satisfied at the Rx end by adding more external memory capacity as well as for facilitating display functions in the form of an off-chip DDR. Latency from encoding to decoding for conventional video decoders is typically more than 100 millisecond.
PLL is an electronic circuit that detects the frequency of an input signal and causes a Voltage-Controlled Oscillator (VCO) to match its output frequency to that of the input signal to effect synchronization. The PLL multiples its reference frequency to a desired output frequency by a ratio of integers. The frequency multiplication is exact, so that the PLL output frequency is precisely locked to the reference frequency. Therefore, if the reference frequency changes, the output frequency will then track exactly Conventional Phase-Locked Loop (PLL) typically includes a reference divider, a phase detector, a charge pump, a loop filter, a voltage-controlled oscillator (VCO) and a feedback divider. A post divider is often added for additional flexibility. The PLL works by adjusting the VCO speed faster or slower in response to the input and feedback clocks available at the phase detector inputs. A small value for the feedback and reference dividers increases the rate at which the phase detector is corrected by a clock signal.
Because video decoder module for conventional wireless video/audio transmitter receiver system requires of having an off-chip DDR memory to achieve the proper operation of the transmitter receiver system thereof, therefore, there is room for improvement in the art.
One aspect of the invention is to provide a wireless video/audio data transmission system capable of adjusting a plurality of Phase-Locked Loop (PLL) parameters to synchronize the rate of clock reference information transmission from a data stream in a decoder module.
One aspect of the invention is to provide a wireless video/audio data transmission system capable of adjusting a plurality of Phase-Locked Loop (PLL) parameters to synchronize the rate of clock reference information transmission from a data stream in a encoder module.
Another aspect of the invention is to provide a wireless video/audio data transmission system without using an external DDR memory acting as the frame buffer.
Another aspect of the invention is to provide a wireless video/audio data transmission system using an on-chip internal SRAM memory acting as the frame buffer.
Another aspect of the invention is to provide a wireless video/audio data transmission system for processing pixel data or frame images under the compressed domain at the decoder module using the on-chip SRAM memory.
To achieve the foregoing and other aspects, the synchronization of the reference frequency in the decoder with the reference frequency in the encoder allows for having a smaller frame buffer in the form of an on-chip SRAM memory to be effectively utilized without having problems relating to displaying faulty images. Moreover, by synchronizing the reference frequency in the decoder with the reference frequency in the encoder, the frame buffer size can be effectively optimized to the extent that even the smaller frame buffer capacity of the SRAM found on-chip can be used to adequately and effectively support the needs for cache memory of the video decoder without requiring of having any larger off-chip DDR memory.
To achieve the foregoing and other aspects, underflow issues in the cache memory or frame buffer would be overcome by speeding up the encoder clock at the transmitter by sending periodic message from the decoder module.
To achieve the foregoing and other aspects, wireless transmission of video/audio data streams at for example 720 p or 1080 p are utilized.
To achieve the foregoing and other aspects, the PLL is configured to resolve discrepancies in reference frequency synchronization between the encoder and decoder modules caused by fluctuating time delay.
To achieve the foregoing and other aspects, the SRAM is disposed on the decoder IC of the decoder module.
To achieve the foregoing and other aspects, an adjusting circuit for adjusting the reference frequency in the decoder module with respect to the reference frequency in the encoder module so as to be synchronized is provided, wherein the adjusting circuit can be a PLL circuit.
To achieve the foregoing and other aspects, a plurality of timestamps, each sent at a set interval in the packet header is provided for detecting a timing difference in the encoder and the decoder, so that the PLL at the decoder can be adjusted up when the reference frequency of the encoder is too high and the corresponding timestamp value at the encoder is too low in comparison to the corresponding timestamp value at the decoder. In addition, the PLL at the decoder can be adjusted down when the reference frequency of the encoder is too low and the corresponding timestamp value at the encoder is too high in comparison to the corresponding timestamp value at the decoder.
To achieve the foregoing and other aspects, the counters used at the encoder and decoder are of 32 bits counters containing the timestamp values.
To achieve the foregoing and other aspects, the PLL includes a reference divider, a phase detector, a charge pump, a loop filter, a voltage-controlled oscillator (VCO) and a feedback divider. The PLL works by adjusting the VCO speed faster or slower in response to the input and feedback clocks available at the phase detector inputs. A small value for the feedback and reference dividers increases the rate at which the phase detector is corrected by a clock signal.
To achieve the foregoing and other aspects, a High-Definition Multimedia Interface (HDMI) I/O connector for transmitting uncompressed streams is provided between any compatible digital audio/video source, such as a set-top box, a DVD player, a PC, a video game console, or an audio video (AV) receiver and a compatible digital audio and/or video monitor, such as a digital television (DTV) to the decoder module at the receiver.
To achieve the foregoing and other aspects, a control logic generates a beacon pulse to be transmitted wirelessly as a control signal from the decoder to the encoder at a regular, predetermined period of the decoder local clock.
To achieve the foregoing and other aspects, the decoder uses a local clock to determine the timing of the data stream according to the timestamps value, and the encoder local clock and the decoder local clock are synchronized.
To achieve the foregoing and other aspects, the wireless encoder module and decoder module may communicate uni-directionally or bi-directionally.
To achieve the foregoing and other aspects, synchronization of the decoder sections with the channel is accomplished through the use of a PCR in the transport stream. The PCR is a timestamp and is used to derive the decoder timing.
The components in the drawings are not necessarily drawn to scale, the emphasis instead placed upon clearly illustrating the principles of the present disclosure. Moreover, in the drawings, like reference numerals designate corresponding parts throughout the several views.
Certain terms are used throughout the description and following claims to refer to particular components. As one skilled in the art will appreciate, electronic equipment manufacturers may refer to a component by different names. This document does not intend to distinguish between components that differ in name but not function. In the following description and in the claims, the terms “include” and “comprise” are used in an open-ended fashion, and thus should be interpreted to mean “include, but not limited to . . . ”. Also, the term “couple” is intended to mean either an indirect or direct electrical connection. Accordingly, if one device is coupled to another device, that connection may be through a direct electrical connection, or through an indirect electrical connection via other devices and connections.
According to a first embodiment of present application, a wireless video/audio transmission system 10 is provided. Referring to
Referring again to
In the first embodiment, the system clock oscillates with +/−30 ppm tolerance. In addition, in the embodiments, a plurality of data streams contain video, audio, timing information and control data are packaged and transmitted as a composite whole. The data, control elements, timing information and other information are arranged in accordance with MPEG-4, h.264/AVC standard. The timing information is used to synchronize the decoding and presentation of the video and audio data. Referring to
According to the embodiments of instant application, a larger external DDR memory acting as the frame buffer is omitted, and instead at least one SRAM 40 is found in the decoder module 35. The SRAM 40 is a smaller pre-existing on-chip internal SRAM found on the decoder IC 50. The operating performance of the SRAM 40 is faster than the conventional DDR memory. According to a third embodiment, transmission latency for using the SRAM 40 has been achieved to be around 50 milliseconds from encoding to decoding as compared to be around 100 millisecond for latency in conventional system. According to a fourth embodiment, the frame buffer or cache can be implemented with a custom voltage scalable SRAM to minimize memory access power, and the SRAM 40 can be a single-port on-chip SRAM cache.
In the first embodiment, the receiver 25 is a receiver with a HDMI interface which must support an input reference clock frequency range of 25 MHz to 165 MHz. In the first embodiment, the encoder module 30 at the transmitter 20 is a wireless module, and generates a local clock, the cycles of the local clock is counted during a common timing reference period maintained wirelessly between the encoder module 30 and the decoder module 35, a timestamp 80 of the decoder clock is received during the same common timing reference period, and the local clock signal of the encoder module 30 is then adjusted based upon a comparison of the two timestamps 80a, 80b (of the encoder clock with respect to the decoder clock). For the first embodiment, the wireless decoder module 35 further receives timing references from the encoder module 30 and, in addition, receives packets of data samples from the encoder module 30 accompanied by a timestamp 80, the timestamp 80 is based upon the encoder timing reference, and outputs the data sample at the time designated by the timestamp 80. In the embodiments, the wireless encoder module 30 and the wireless decoder module 35 may communicate unidirectionally or bidirectionally.
Referring to
In a fifth embodiment, video data and audio data are encoded into a plurality of elementary video and audio bitstreams at the encoder module 30. These bitstreams are then converted into packets. The packets are received and multiplexed to produce a transport stream. The transport stream is transmitted over a transmission channel, which may further incorporate separate channel specific encoder and decoder (not shown). Next, the transport stream is demultiplexed and decoded by a transport stream demultiplexor (not shown), where the elementary bitstreams serve as inputs to the decoder module 35. Referring to
According to the embodiments of instant application, overall memory usage for the wireless video/audio transmission system is reduced by omitting a larger external DDR memory acting as the frame buffer, to use instead, a much smaller internal SRAM. As a result, the quantity of memory components for the wireless video/audio transmission system is reduced by eliminating the DDR memory. In the conventional art, only fully-processed pixels are stored in the off-chip memory of the DDR. On the other hand, pixel data in compressed domain are stored in the SRAM 40 according to the embodiments of instant application.
Although the illustrative embodiments have been described herein with reference to the accompanying drawings, it is to be understood that the present invention is not limited to those precise embodiments, and that various changes and modifications may be effected therein by one of ordinary skill in the pertinent art without departing from the scope or spirit of the present invention. All such changes and modifications are intended to be included within the scope of the present invention as set forth in the appended claims.
