Abstract:
An integrated circuit multiplexes transmission data faster than by a system clock, and transfers a timing pulse Txclk for that multiplexing and a multiplexed signal Txdata from a transmitter chip  100  to a receiver chip  150  through communications by inductive coupling, respectively. Because of a transfer by inductive coupling being broadband, close-proximity wireless communications, the receiver chip  150  can faithfully obtain timing information on the timing pulse Txclk including jitter generated by a simple oscillator, and can thus accurately restore original data even by a high-speed transmission. This allows, in an integrated circuit that carries out communications by inductive coupling between chips to be stacked and mounted, carrying out communications between semiconductor chips with a small required area and faster than by a system clock.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to an integrated circuit that is capable of suitably carrying out communications between chips such as IC (Integrated Circuit) bare chips to be stacked and mounted. 
         [0003]    2. Description of the Related Arts 
         [0004]    The present inventors have proposed electronic circuits that carry out communications by inductive coupling between chips to be stacked and mounted via coils formed by on-chip wiring of LSI (Large Scale Integration) chips (refer to Patent Literature 1). 
         [0005]      FIG. 5  is a view depicting a configuration of a conventional (first) transmitter and receiver circuit. A part thereof is shown also in Patent Literature 1.  FIG. 6  is a view depicting waveforms of respective portions of the circuit shown in  FIG. 5 . A transmitter circuit  300  is composed of a pulse generator  311 , an inverter  312 , a NOR circuit  313 , transistors  314 ,  315 , an inverter  316 , a NOR circuit  317 , transistors  318 ,  319 , and a transmitter coil  320 . The pulse generator  311  generates a pulse having a pulse width determined by a propagation delay of an inverter delay line in synchronization with a rising edge of a transmission clock Txclk. The pulse is input to an H-bridge circuit, and if a transmission signal Txdata is high at the rising edge of the transmission clock Txclk, the H-bridge circuit allows a positive (arrow direction in the figure) pulse current IT (if the transmission signal Txdata is low, a negative pulse current IT) to flow through the transmitter coil  320 . With this construction, a positive or negative triangular wave current IT flows through the transmitter coil  320  according to the transmission signal Txdata at the rising edge of the transmission clock Txclk. 
         [0006]    A receiver circuit  350  is composed of a receiver coil  340 , resistors  321 ,  322 , transistors  323  to  332 , NAND circuits  333 ,  334 , and inverters  335 ,  336 , and forms a comparator with a latch in its entirety. The receiver circuit  350  receives a receiving clock (synchronization signal) Rxclk externally and outputs receiving data Rxdata. The transistors  323 ,  324  constitute a differential pair of a differential amplifier, and receive a signal VR from the receiver coil  340 . The NAND circuits  333 ,  334  form a latch. The data received by the differential amplifier is sampled in synchronization with the receiving clock Rxclk to be input into the transistors  323  to  325 ,  329 , and  331 , and latched by the NAND circuits  333 ,  334 , whereby the receiving signal Rxdata is restored. 
         [0007]    This transmitter and receiver circuit is a synchronous type in which a system clock is used for reproduction of data. Accordingly, the data transfer rate is limited by the system clock. 
         [0008]    Therefore, it has been proposed to synchronize high-speed data with timing pulses by independently having high-speed ring oscillators for generating timing pulses at the transmission side and the reception side, respectively, and sending signals to control the oscillation start/stop thereof parallel to transmitting data (refer to Non Patent Literature 1). 
         [0009]      FIG. 7  is a view depicting a configuration of a conventional (second) transmitter and receiver circuit.  FIG. 8  is a view depicting waveforms of respective portions of the circuit shown in  FIG. 7 . The transmission side is composed of a control circuit  411 , an n-bit counter  412 , a ring oscillator  413 , a module ( 1 )  414 , and a 2 n :1 multiplexer  415 . The control circuit  411  operates based on an fHz system clock and supplies a reset pulse to the n-bit counter  412  (for example n=4). The n-bit counter  412  is reset by the reset pulse to make a timing signal Txstop as its MSB low, whereupon pulses are generated by the ring oscillator  413 , and the n-bit counter  412  counts the pulses. The n-bit counter  412 , when the n-bit counter  412  counts 2 n-1  (for example 8) pulses, makes the timing signal Txstop high to stop pulse generation by the ring oscillator  413 . The 2 n :1 multiplexer  415  multiplexes 2 n  (for example 16) parallel fb/s transmission data Mtxdata from the module ( 1 )  414  2 n  times by rising and falling of a transmission timing pulse Txclk and transmits the multiplexed data as a 2 n  fb/s serial transmission signal Txdata. 
         [0010]    The timing signal Txstop is transmitted by a non-chip wiring  421  from the transmission side to the reception side, and the transmission signal Txdata, by an on-chip wiring  422 . 
         [0011]    The reception side is composed of a ring oscillator  431 , a 1:2 n  demultiplexer  432 , and a module ( 2 )  433 . The ring oscillator  431  receives a timing signal Rxstop corresponding to the timing signal Txstop to generate a receiving timing pulse Rxclk, and supplies the same to the 1:2 n  demultiplexer  432 . The 1:2 n  demultiplexer  432  receives a receiving signal Rxdata corresponding to the transmission signal Txdata, demultiplexes the same to 2 n  parallel fb/s receiving data Mrxdata by the receiving timing pulse Rxclk, and supplies the demultiplexed data to the module ( 2 )  433 . 
         [0012]    However, while this technique is on the assumption that the respective ring oscillators have the same characteristics, in different chips, ring oscillators on the respective chips greatly differ in characteristics due to manufacturing variations despite being of the same design, the difference in chips results in a difference in power supply voltage, and it is thus difficult to match the timing of pulses to be generated by the ring oscillator in each chip, and this technique is not suitable for communications between chips. 
         [0013]      FIG. 9  is a view depicting a configuration of a reference (third) transmitter and receiver circuit. This is an example where a transmitter chip  500  and a receiver chip are connected by wiring therebetween, and a multiplexed signal and a timing pulse of multiplication are respectively transmitted from the transmitter chip  500  to the receiver chip to perform demultiplexing in the receiver chip  550 . The transmitter chip  500  is composed of a PLL (Phase Locked Loop) and a 2 n :1 multiplexer  515 . The PLL  510  is composed of a PFD (Phase Frequency Detector)  511 , a CP (Charge Pump)  512 , a VCO (Voltage Controlled Oscillator)  513 , and a ½ n-1  frequency divider  514 , and generates a 2 n-1  fHz transmission timing pulse Txclk from an fHz system clock and supplies the same to the 2 n :1 multiplexer  515 . The 2 n :1 multiplexer  515  multiplexes 2 n  parallel fb/s transmission data Mtxdata 2 n  times by the transmission timing pulse Txclk and transmits the multiplexed data as a 2 n fb/s serial transmission signal Txdata. 
         [0014]    The transmission timing pulse Txclk is transmitted by an interchip wiring  521  from the transmitter chip  500  to the receiver chip  550 , and the transmission signal Txdata, by an interchip wiring  522 . 
         [0015]    The receiver chip  550  is composed of a 1:2 n  demultiplexer  531 , which receives a receiving timing pulse Rxclk corresponding to the transmission timing pulse Txclk, and demultiplexes a 2 n fb/s serial receiving signal Rrxdata into 2 n  parallel fb/s receiving data Mrxdata. 
         [0016]    However, this method can be used for transmission of a continuous clock whose oscillation frequency has been controlled at high accuracy in the PLL, but is not suitable for transmission of a predetermined number of pulses generated by a ring oscillator etc. 
         [0017]      FIG. 10A  and  FIG. 10B  are views for comparing two types of pulse trains.  FIG. 10A  depicts a pulse train by a PLL, and  FIG. 10B  depicts a pulse train by a ring oscillator. As shown in  FIG. 10A , a continuous clock ClkPLL generated in the PLL has been controlled in oscillation frequency with accuracy and thus has less jitter. On the other hand, a pulse train ClkRING of a predetermined number of pulses generated in the ring oscillator of a simpler configuration than the PLL is not stabilized in oscillation frequency, has a large amount of jitter, and contains a higher frequency component than that of the continuous clock ClkPLL. In the data transmission technology shown in  FIG. 9 , due to a band limitation of the interchip wiring, a high frequency component is cut in the course of transmission, so that the jitter of the pulse train ClkRING changes. Therefore, phase information of the pulse train ClkRING when being multiplexed is lost, erroneous phase information is transmitted to the 1:2 n  demultiplexer  531 , so that demultiplexing cannot be correctly performed. 
         [0018]      FIG. 11  is a view depicting a configuration of a conventional (fourth) transmitter and receiver circuit. A part thereof is shown also in Patent Literature 2.  FIG. 12  is a view depicting waveforms of respective portions of the circuit shown in  FIG. 11 . A transmitter circuit  700  is composed of transistors  711  to  714 , a delay line  715 , and a transmitter coil  716 . A receiver circuit  750  is composed of a receiver coil  721  and transistors  722  to  727 . 
         [0019]    This is an example where, when logic of a transmission signal Txdata transits, a positive or negative pulse current IT flows through the transmitter coil  716 , and the receiver circuit  750  restores receiving data Rxdata, as a result of, by inverting data upon a latter-half pulse while ignoring a first-half pulse of a double pulse of a received voltage VR with using a change in threshold value due to latching of a hysteresis comparator. This enables asynchronous inductive coupling communication. 
         [0020]    [Patent Literature 1] US 20070289772 A1 
         [0021]    [Patent Literature 2] JP 2006-050354 A 
         [0022]    [Non Patent Literature 1] S. Kimura et al., “An On-Chip High Speed Serial Communication Method Based on Independent Ring Oscillators,” In Proc. of International Solid-State Circuits Conference (ISSCC2003), pp. 390-391, February 2003. 
       SUMMARY OF THE INVENTION 
       [0023]    However, because the pulse of received voltage VR shown in  FIG. 12  is a positive and negative double pulse to one logic transition of the transmission signal Txdata, the pulse width of the signal must be increased to secure time until generation of a next pulse, so that the transmission rate cannot be made faster. 
         [0024]    In view of the above-described problems, it is therefore an object of the present invention to provide an integrated circuit capable of performing communications between semiconductor chips with a small required area and faster than by a system clock. 
         [0025]    An integrated circuit according to a first aspect of the present invention comprises: 
         [0026]    a transmitter chip including: a pulse generator for generating i (i is an integer i≧2) timing pulses for transmitting data from a system clock; a multiplexer for multiplexing transmission data to j:1 (j is an integer 2≦j≦2i) by the timing pulse; a first transmitter for transmitting by inductive coupling a multiplexed signal multiplexed by the multiplexer; a second transmitter for transmitting the timing pulse by inductive coupling; and 
         [0027]    a receiver chip being stacked and mounted on the transmitter chip including: a first receiver for receiving the multiplexed signal by inductive coupling; a second receiver for receiving the timing pulse by inductive coupling; and a demultiplexer for demultiplexing the multiplexed signal to 1:j by the timing pulse. 
         [0028]    Moreover, an integrated circuit according to a second aspect of the present invention further comprises a phase interpolator for generating an interpolation timing pulse of a 90 degrees phase to the timing pulse from the timing pulse, wherein the demultiplexer demultiplexes the multiplexed signal by the interpolation timing pulse. 
         [0029]    Moreover, in an integrated circuit according to a third aspect of the present invention, the first transmitter comprises a transmitter coil for transmitting the multiplexed signal by inductive coupling, and enters a signal resulting from the multiplexed signal to one end of the transmitter coil and enters a signal resulting from a reverse polarity signal of the multiplexed signal to an other end of the transmitter coil to enter a waveform equivalent to a waveform of the multiplexed signal to the transmitter coil. 
         [0030]    Moreover, in an integrated circuit according to a fourth aspect of the present invention, the first receiver comprises a receiver coil for receiving the multiplexed signal by inductive coupling, and forms a hysteresis circuit that repeats, first, inverting output when a voltage induced in the receiver coil exceeds a first threshold value, secondly, inverting output when a voltage induced in the receiver coil falls under a second threshold value smaller than the first threshold value, thirdly, inverting output when a voltage induced in the receiver coil exceeds the first threshold value, and so on. 
         [0031]    Moreover, in an integrated circuit according to a fifth aspect of the present invention, the first receiver comprises a receiver coil for receiving the multiplexed signal by inductive coupling, and biases a center of the receiver coil toward a predetermined potential, and a circuit for generating a bias voltage is a circuit, having a same configuration as that of the first receiver, whose input and output are short-circuited or short-circuited through resistance. 
         [0032]    According to the integrated circuit of the first aspect of the present invention, this generates a timing pulse faster than a system clock, multiplexes data by the timing pulse, and transmits the timing pulse from the transmitter chip to the receiver chip by inductive coupling, and thus it suffices to generate the timing pulse in the transmitter chip, and because of a transfer by inductive coupling being broadband, close-proximity wireless communications, the receiver chip can faithfully obtain timing information on the timing pulse including jitter generated by a simple oscillator, and can thus accurately restore original data even by a high-speed transmission, and moreover, an area on the chip necessary therefor can also be minimized. 
         [0033]    According to the integrated circuit of the second aspect of the present invention, it is configured so that a rising edge or falling edge of the receiving timing pulse comes in the center of the data cycle of a receiving signal, so that the receiving data can be reliably latched. 
         [0034]    According to the integrated circuit of the third aspect of the present invention, at the transition of the multiplexed signal, a positive or negative unipolar pulse can be induced in the receiver coil, and thus the pulse density can be increased by that much to increase the data transfer rate. 
         [0035]    According to the integrated circuit of the fourth aspect of the present invention, a receiver tolerant of noise can be formed. 
         [0036]    According to the integrated circuit of the fifth aspect of the present invention, a desired bias voltage can be adaptively generated even if the transistor characteristics, power supply voltage, and temperature have fluctuated. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0037]      FIG. 1A ,  FIG. 1B , and  FIG. 1C  are views depicting a configuration of an integrated circuit according to one embodiment of the present invention. 
           [0038]      FIG. 2  is a view depicting a detailed configuration of a transmitter circuit and a receiver circuit of the present embodiment. 
           [0039]      FIG. 3  is a view depicting waveforms of respective portions of the circuits shown in  FIG. 2 . 
           [0040]      FIG. 4  is a view depicting a configuration of a bias generating circuit that generates an input bias voltage. 
           [0041]      FIG. 5  is a view depicting a configuration of a conventional (first) transmitter and receiver circuit. 
           [0042]      FIG. 6  is a view depicting waveforms of respective portions of the circuit shown in  FIG. 5 . 
           [0043]      FIG. 7  is a view depicting a configuration of a conventional (second) transmitter and receiver circuit. 
           [0044]      FIG. 8  is a view depicting waveforms of respective portions of the circuit shown in  FIG. 7 . 
           [0045]      FIG. 9  is a view depicting a configuration of a reference (third) transmitter and receiver circuit. 
           [0046]      FIG. 10A  and  FIG. 10B  are views for comparing two types of pulse trains. 
           [0047]      FIG. 11  is a view depicting a configuration of a conventional (fourth) transmitter and receiver circuit. 
           [0048]      FIG. 12  is a view depicting waveforms of respective portions of the circuit shown in  FIG. 11 . 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0049]    Hereinafter, a detailed description is given of a best mode for carrying out the present invention with reference to the accompanying drawings. 
         [0050]      FIG. 1A ,  FIG. 1B , and  FIG. 1C  are views depicting a configuration of an integrated circuit according to one embodiment of the present invention.  FIG. 1A  depicts a configuration of the embodiment,  FIG. 1B  depicts waveforms of respective portions of the embodiment, and  FIG. 1C  depicts a configuration of a phase interpolator. A transmitter chip  100  is composed of a control circuit  11 , an n-bit counter  12 , a ring oscillator  13 , a transmitter circuit  14 , a transmitter coil  15 , a 2 n :1 multiplexer  21 , a transmitter circuit  22 , and a transmitter coil  23 . An operation to generate a transmission timing pulse Txclk and an operation to demultiplex transmission data Mtxdata are the same as those shown in  FIG. 7 . In the present embodiment, the transmission timing pulse Txclk is transmitted to a receiver chip  150  by inductive coupling via the transmitter circuit  14  and the transmitter coil  15 , and a transmission signal Txdata is transmitted to the receiver chip  150  by inductive coupling via the transmitter circuit  22  and the transmitter coil  23 . 
         [0051]    The receiver chip  150  is composed of a receiver coil  31 , a receiver circuit  32 , a phase interpolator  33 , a receiver coil  41 , a receiver circuit  42 , a dummy phase interpolator  43 , and a 1:2 n  demultiplexer  44 . Although an operation of demultiplexing is the same as that shown in  FIG. 7 , in the present embodiment, a receiving timing pulse Rxclk corresponding to the transmission timing pulse Txclk is received via the receiver coil  31  and the receiver circuit  32 , and the phase is shifted by 90 degrees in the phase interpolator  33  so that a rising edge or falling edge of the receiving timing pulse Rxclk comes in the center of the data cycle of a receiving signal Rxdata, thereby enabling reliably latching the receiving data Rxdata. 
         [0052]    As shown in  FIG. 1C , the phase interpolator  33  is composed of transistors  51 ,  52 ,  54 , and  55 , current sources  53 ,  56 , and resistors  57 ,  58 . These interpolate from two inputs of 0 degrees and 180 degrees to output a signal of 90 degrees being an intermediate phase therebetween. The dummy phase interpolator  43  cancels out a delay of the phase interpolator  33  itself, thereby always providing a phase difference of 90 degrees between the receiving signal Rxdata and the receiving timing pulse Rxclk. 
         [0053]      FIG. 2  is a view depicting a detailed configuration of a transmitter circuit and a receiver circuit of the present embodiment.  FIG. 3  is a view depicting waveforms of respective portions of the circuits shown in  FIG. 2 . The transmitter circuit  22  is composed of transistors  111  to  114 . These are directly driven by a transmission signal Txdata to allow a transmission current IT having the same waveform shape as that of the transmission signal Txdata to flow through the transmitter coil  23 . Via an inductive coupling channel, positive and negative pulse voltages are generated in the receiver coil  41 . 
         [0054]    The receiver circuit  42  is composed of transistors  122  to  127 . The receiver coil  41  has been biased to a voltage VB of about half the power supply voltage, and a positive pulse voltage with reference to this voltage is generated when the transmission signal Txdata changes from low to high, and when the transmission signal Txdata changes from high to low, a negative pulse voltage is generated. 
         [0055]    The receiver circuit  42  forms a hysteresis comparator, which is composed of a gain circuit and a latch circuit. The gain circuit is inverters composed of ‘a transistor  122  and a transistor  124 ’ and ‘a transistor  125  and a transistor  127 ’, which connect both terminals of the receiver coil  41  to the gates to amplify a pulse voltage VR to be input. The receiving data Rxdata is inverted when the pulse voltage VR exceeds a certain threshold value. The latch circuit is cross-coupled PMOS transistors connected to the output of the inverters. This circuit has a function of holding the receiving signal Rxdata, thereby enabling correctly restoring digital data from the pulse voltage VR. This latch circuit changes the threshold value of an input inverter according to the holding data. A dotted line shown in the VR waveform of  FIG. 3  indicates a change in threshold value of the inverter composed of the transistor  122  and the transistor  124 . In the initial state, the latch circuit that holds a low receiving signal Rxdata raises the threshold value of the inverter by +Vth. The receiving signal Rxdata is inverted to be high when a positive pulse is input to the input and exceeds this threshold value. The latch circuit now reduces the threshold value of the inverter by −Vth, and holds the receiving signal Rxdata until a negative pulse voltage exceeding the threshold value is input next. Repeating this allows correctly restoring digital data from the positive and negative pulse voltages. 
         [0056]    The transmitter and receiver circuit  22 ,  42  is an asynchronous type in which no clock is required for restoration of receiving data. It is not necessary to increase, as in the conventional synchronous type, the pulse width so as to keep a sampling margin. Accordingly, the data transfer rate is never limited by timing constraints as in the synchronous type. 
         [0057]    Making the receiver circuit  42  operate at a high sensitivity enables receiving short-width pulses, thereby allowing increasing the data transfer rate. 
         [0058]    The sensitivity of the receiver circuit  42  is determined by the input bias voltage VB. Adjusting the VB with accuracy to a point where the hysteresis comparator can operate at the highest sensitivity enables a high-speed operation. 
         [0059]      FIG. 4  is a view depicting a configuration of a bias generating circuit that generates an input bias voltage. The bias generating circuit, for which the input and output of a hysteresis comparator the same as that used for the receiver circuit  42  are short-circuited, and further, differential outputs are short-circuited, automatically generates a bias voltage to allow the hysteresis comparator to operate at the highest sensitivity. Moreover, the bias generating circuit is formed of a replica circuit that is exactly the same also in transistor size as the receiver circuit  42  body. This allows adaptively generating a desired bias voltage even if the transistor characteristics, power supply voltage, and temperature have fluctuated. 
         [0060]    However, the present invention is not limited to the above-described embodiment. 
         [0061]    In the embodiment of the present application, an example has been mentioned of multiplexing to a frequency of twice that of the timing pulses, however, the invention is not limited thereto. For example, those may be equalized, and even more timing pulses will not affect the implementation. 
         [0062]    As the phase interpolator, an example that generates an interpolation timing pulse of a 90 degrees phase to the timing pulse has been mentioned, however, a latch timing pulse may be prepared by a delay, and the multiplexed signal may be delayed. 
         [0063]    As the transmitter circuit, an example that supplies multiplexed signals of different polarities to both ends of the transmitter coil has been described, however, this may be configured such as to supply a multiplexed signal to one end of the transmitter coil and ground the other end via a capacitor. 
         [0064]    As the receiver circuit, an example having hysteresis characteristics in the threshold value has been mentioned, however, this may be configured so as to detect a signal exceeding a first threshold value or below a second threshold value and ignore an intermediate signal therebetween. 
         [0065]    As the bias circuit, an example using transistors having the same characteristics as those of the hysteresis circuit has been mentioned, however, when a high accuracy is not necessary such as when being used in a stable environment, this may be implemented even by a simple resistance circuit. 
         [0066]    Although an example where the transmitter chip and the receiver chip are stacked and mounted has been mentioned, the invention is not limited thereto, and may be, for example, a configuration where each chip has a transmitter circuit and a receiver circuit. 
         [0067]    The disclosure of Japanese Patent Application No. 2008-023397, filed on Feb. 2, 2008 including its specification, claims and drawings, is incorporated herein by reference in its entirety. 
         [0068]    All the publications, patents and patent applications cited in the present specification are taken in the present specification as references.