Patent Application
20090141846
1. Field of the Invention
The present invention relates to a receiving apparatus that can be connected to a transmitting apparatus through a plurality of transmission lines and its receiving method.
2. Description of the Related Art
A conventional inter-chip transmission system will be described below.
At power-on time or hard rest time, each chip determines bit synchronization, symbol synchronization, deskew between lanes, link width, lane order, link data rate, before activation of the link. The link width is set to a largest possible value, and data rate is set to a highest possible value. At the activation time, optimization of a transmission waveform or optimization of a reception waveform according to a state of the transmission system is not performed.
Data check is performed in a data link layer and, when a plurality (e.g., three times) of consecutive reception errors take place, it is determined that link abnormality has occurred, and link down is made. A coding method and an error correction method are fixed irrespective of transmission quality of the transmission system.
The above link can assume four states: 0, 0s, 1, and 2. The state 0 is a normal operating state. The state 0s is a state where transmission operation is stopped but CDR and CLK operate. The state 1 is a state where transmission operation is stopped and CDR and CLK are also stopped. The state 2 is a state where transmission operation is stopped and CDR, CLK, and main power supply are stopped.
The states 0s, 1, and 2 are compared with one another. The state 0s has a smaller effect of power reduction and a shorter wake-up time. The state 1 has a moderate effect of power reduction and a moderate wake-up time. The state 2 has a larger effect of power reduction and a longer wake-up time.
An inter-chip transmission system including a transmitting chip and a receiving chip will next be described.
All the transmitting circuits 11 operate according to an externally supplied common basic clock.
When parallel transmission data synchronized with a clock is input to the transmitting circuit, the encode circuit 111 performs 8B/10B coding for the transmission data to shorten the length of consecutive identical digits, embeds a basic clock component in the resultant data, and performs parallel-to-serial conversion, to thereby output a serial signal. The FFE 112 pre-emphasizes a harmonic component of the serial signal. The amplifier 113 in the last stage of the transmitting circuit amplifies the amplitude of the supplied signal to a required amplitude and makes impedance matching between the resultant signal and transmission line to thereby drive the transmission path. The FFE 112 in this example is a three-tap FFE, and the tap coefficients K0 to K2 are set in accordance with the emphasis amount. The gain K3 of the amplifier 113 is set so that the output amplitude has a predetermined value.
The CDR 121 is constituted by a PLL (Phase Locked Loop) circuit. The PLL circuit is constituted by a phase comparison circuit, a charge pump, a low-pass filter, a VCO, and an M/N division circuit. The PLL circuit compares timing information (edge) of input data and timing information (edge) of VCO (Voltage Controlled Oscillator) output to thereby generate a clock synchronized with input data.
The DECISION circuit 122 determines input data (DATA-IN) transmitted from the transmitting circuit 11 at the timing of a clock output from the CDR 121.
What is required for the PLL circuit is to take in, without fail, the input data with a reasonable take-in time, to keep a locked state with every input data pattern, to have excellent output jitter characteristics, to prevent jitter from increasing in every input data pattern, and to keep a locked state even with data containing consecutive identical digits while preventing output clock jitter from increasing. In high-speed transmission in which the transmission rate exceeds gigabits per second (Gbps), level of the requirements gets higher, so that it is impossible to satisfy the requirements with the abovementioned fundamental configuration.
In order to cope with the above problem, there is proposed a PLL circuit modified such that the output clock jitter of the PLL circuit is not increased even when the transition rate of the input data is low (refer to, e.g., Patent Document 1: Jpn. Pat. Appln. Laid-Open Publication No. 2004-88476). The PLL circuit of Patent Document 1 is about twice the scale of a PLL circuit having a basic configuration.
Further, there is proposed a PLL circuit modified in order to satisfy jitter transfer and jitter tolerance characteristics of the PLL circuit at a specified operating temperature and within a range of power supply voltage (refer to, e.g., Patent Document 2: Jpn. Pat. Appln. Laid-Open Publication No. 2002-359555). A potential generation circuit used in the PLL circuit of Patent Document 2 is created based on a BGR (Band Gap Reference) circuit, so that the scale of this PLL circuit becomes larger than that of a PLL circuit having a basic configuration.
In order to widen the capture range and lock range of the PLL, it is only necessary to widen the PLL loop bandwidth. However, in order to achieve stable operation with a longer consecutive identical digit pattern, the PLL loop needs to be narrowed. In order to realize the opposite requirements, there is proposed a PLL circuit having a loop that locks onto a reference clock and a loop that locks onto input data (refer to, e.g., Patent Document 3: Jpn. Pat. Appln. Laid-Open Publication No. 2005-210540). The PLL circuit of Patent Document 3 requires the reference clock, and the scale thereof becomes larger than that of a PLL circuit having a basic configuration.
As described above, when the performance of the PLL circuit is increased in order to speed up transmission speed, the scale of the circuit is increased, resulting in an increase in power consumption and cost.
The present invention has been made to solve the above problem, and an object thereof is to provide a receiving apparatus and a receiving method capable of suppressing increase in the circuit scale.
To solve the above problem, according to an aspect of the present invention, there is provided a receiving apparatus that can be connected to a transmitting apparatus through a plurality of transmission lines, including: a first clock generation section that generates a first clock based on a signal from a first transmission line which is one of the plurality of transmission lines; a first demodulation section that demodulates the signal from the first transmission line based on the timing of the first clock; a second clock generation section that controls the phase of the first clock based on the phase of a signal from a second transmission line which is one of the plurality of transmission lines and is different from the first transmission line to generate a second clock; and a second demodulation section that demodulates a signal from the second transmission line based on the timing of the second clock.
Further, according to another aspect of the present invention, there is provided a receiving method by which a receiving apparatus connected to a transmitting apparatus through a plurality of transmission lines receives a signal from the plurality of transmission lines, including: generating a first clock based on a signal from a first transmission line which is one of the plurality of transmission lines; demodulating the signal from the first transmission line based on the timing of the first clock; controlling the phase of the first clock based on the phase of a signal from a second transmission line which is one of the plurality of transmission lines and is different from the first transmission line to generate a second clock; and demodulating a signal from the second transmission line based on the timing of the second clock.
According to the present invention, it is possible to suppress increase in the scale of a circuit for data reception in an inter-chip transmission system.
Embodiments of the present invention will be described below with reference to the accompanying drawings.
A configuration of an inter-chip transmission system according to a first embodiment will first be described.
A reception signal which is a received transmission waveform is terminated in a matched impedance level by the amplifier 31 in the first stage to be amplified. The gain K4 of the amplifier 31 is set so that the amplitude of the reception signal has a required value. The equalizer coefficients K5 to K7 of the EQ32 are set so that the reception signal has required equalization characteristics (frequency characteristics).
The DEF 33 is an equalizer that uses a digital filter and has a SLICER and four taps. The DEF 33 makes the frequency characteristics flat without amplifying noise or crosstalk. The DEF 33 ensures a voltage margin of the SLICER in the DFE 33 even when receiving consecutive identical digits to suppress pattern dependant jitter. The SLICER uses the data clock to perform data determination of a signal obtained by synthesizing the input data and a signal that has returned thereto through the four taps.
The decoding circuit 34 converts a high-speed serial signal into a parallel signal and performs decoding such as 8B/10B scheme.
The clock distribution circuit 36 distributes the data clock output from the CDR 35 to the n receiving circuits 21b (RX1 to RXn).
The phase control circuit 37 controls the phase of the data clock output from the CDR 35 of the receiving circuit 21a to an optimum phase for the its own reception signal. The data clock output from the phase control circuit 37 is input to the SLICER of the DFE 33 and the decoding circuit 34.
The multiphase clock generation circuit 41 outputs, based on the data clock output from the CDR 35 of the receiving circuit 21a, p clocks (φ0, φ1, . . . , φp-1) having different phases.
The clock selection circuit 42 includes p phase comparison circuits 43 and a determination circuit 44. The phase comparison circuit 43 compares the phases of the data clock φi output from the multiphase clock generation circuit 41 and input data (DATA-IN) and outputs, as a comparison result, one of “advanced phase” (the phase of the data clock φi is advanced with respect to the phase of the input data), “coincidence” (the phase of the data clock φi coincides with the phase of the input data), and “delayed phase” (the phase of the data clock φi is delayed with respect to the phase of the input data). The determination circuit 44 selects, from the p data clocks output from the multiphase clock generation circuit 41, a clock whose phase coincides with the phase of the input data based on the comparison results of the p phase comparison circuits 43 and outputs the selected clock.
According to the present embodiment, the scale of the phase control circuit 37 provided in the receiving circuit 21b is smaller than that of the CDR 35 provided in the receiving circuit 21a. That is, it is only necessary for the receiving chip 2a to have only one receiving circuit 21a having the CDR 35 whose circuit scale is large, enabling high-quality data transmission while suppressing increase in the circuit scale of the receiving chip and chip size. As a result, it is possible to perform high-speed data transmission while suppressing power consumption of the receiving chip.
A configuration of an inter-chip transmission system according to a second embodiment will first be described.
The multiphase clock generation circuit 41b generates p data clocks φ0, φ1,. . . , φp-1 having different phases based on the N-multiplied clock from the CDR 35b.
Assuming that one of the n receiving circuits 21d is RXj (j=1, 2, . . . , n), the clock distribution circuit 52 selects one data clock from the p data clocks output from the multiphase clock generation circuit 41b according to a phase comparison result output from the RXj and supplies the selected data clock to the RXj.
In this example, the phase comparison result indicates one of “advanced phase”, “coincidence”, and “delayed phase”. In the case where the comparison result received from the RXj is “advanced phase”, the clock distribution circuit 52 supplies a data clock obtained by delaying the current data clock by half a clock cycle to the RXj. In the case where the comparison result received from the RXj is “delayed phase”, the clock distribution circuit 52 supplies a data clock obtained by advancing the current data clock by half a clock cycle to the RXj. In the case where the comparison result received from the RXj is “coincidence”, the clock distribution circuit 52 supplies the current data clock to the RXj without modification.
An example of the data clock will next be described.
As shown in
Assuming that RXj performs data determination of the DATA-IN at the rising edge of the data clock, the data clock φ4 is appropriate. Thus, in the case where the data clock from the receiving circuit 21c is φ4, the phase comparison circuit 43 of the RXj transmits, to the receiving circuit 21c, a result indicating “coincidence”, and the receiving circuit 21c transmits φ4 to the RXj ongoingly. In the case where the data clock from the receiving circuit 21c is φ3, the phase comparison circuit 43 of the RXj transmits, to the receiving circuit 21c, a result indicating “advanced phase”, and the receiving circuit 21c delays φ3 by half a clock cycle of the N-multiplied clock to obtain φ4 and transmits φ4 to the RXj. In the case where the data clock from the receiving circuit 21c is φ5, the phase comparison circuit 43 of the RXj transmits, to the receiving circuit 21c, a result indicating “delayed phase”, and the receiving circuit 21c advances φ5 by half a clock cycle of the N-multiplied clock to obtain φ4 and transmits φ4 to the RXj.
According to the present embodiment, the scale of the phase comparison circuit 43 provided in the receiving circuit 21d is smaller than that of the CDR 35b provided in the receiving circuit 21c. That is, it is only necessary for the receiving chip 2a to have only the receiving circuit 21a having the CDR 35 whose circuit scale is large, enabling high-quality data transmission while suppressing increase in the circuit scale of the receiving chip. As a result, it is possible to perform high-speed data transmission while suppressing power consumption of the receiving chip.
A configuration of an inter-chip transmission system according to a third embodiment will first be described.
The receiving circuits 21d and 21f belonging to the same block have the same wiring length between themselves and corresponding transmitting circuits 11 of the transmitting chip 1. For example, it is assumed that one receiving circuit 21d is RXi, and that RXi+1 and RXi+2 which are two receiving circuits 21f belong to the same group as the RXi. Further, it is assumed, in the transmitting chip 1, that the transmitting circuits 11 connected respectively to the RXi, RXi+1, and RXi+2 is TXi, TXi+1, and TXi+2. In this case, the wiring between the TXi and RXi, wiring between the TXi+1 and RXi+1, and wiring between the TXi+2 and RXi+2 have the same length.
Assuming that one of the m blocks is a k-th block (k=1, 2, . . . , m), the clock distribution circuit 52c selects, according to a phase comparison result input thereto from the receiving circuit 21d of the k-th block, one data block from p data clocks input thereto from the multiphase clock generation circuit 41b and supplies the selected data clock to the receiving circuits 21d and 21f belonging to the k-th block.
As in the case of the second embodiment, the phase comparison result indicates one of “advanced phase”, “coincidence”, and “delayed phase”. In the case where the comparison result received from the receiving circuit 21d belonging to the k-th block is “advanced phase”, the clock distribution circuit 52c supplies a data clock obtained by delaying the current data clock by half a clock cycle to the receiving circuits 21d and 21f belonging to the k-th block. In the case where the comparison result received from the receiving circuit 21d belonging to the k-th block is “delayed phase”, the clock distribution circuit 52c supplies a data clock obtained by advancing the current data clock by half a clock cycle to the receiving circuits 21d and 21f belonging to the k-th block. In the case where the comparison result received from the receiving circuit 21d belonging to the k-th block is “coincidence”, the clock distribution circuit 52c supplies the current data clock to the receiving circuits 21d and 21f belonging to the k-th block without modification.
The receiving circuit 21d according to the present embodiment has the same configuration as that of the receiving circuit 21d according to the second embodiment.
Since the receiving circuits 21d and 21f belonging to the same block have the same wiring length between themselves and corresponding transmitting circuits 11, a clock controlled for the receiving circuit 21d in a given block can be used for the receiving circuit 21f belonging to the same block as the given block.
According to the present embodiment, the scale of the phase comparison circuit 43 provided in the receiving circuit 21d is smaller than that of the CDR 35b provided in the receiving circuit 21e. Further, the scale of the receiving circuit 21f is smaller than that of the receiving circuit 21d. It is only necessary for the receiving chip 2a to have only one receiving circuit 21a and have one receiving circuit 21d for each block, enabling high-quality data transmission while suppressing increase in the circuit scale of the receiving chip. As a result, it is possible to perform high-speed data transmission while suppressing power consumption of the receiving chip.
The present invention can be embodied in various forms, without departing from the spirit or the main feature. Therefore, the aforementioned embodiments are merely illustrative of the invention in every aspect, and not limitative of the same. The scope of the present invention is defined by the appended claims, and is not restricted by the description herein set forth. Further, various changes and modifications to be made within the scope of the appended claims and equivalents thereof are to fall within the scope of the present invention.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2007-313802 | Dec 2007 | JP | national |
