Abstract:
A first charging circuit that includes a diode and a capacitor, and a second charging circuit that similarly includes a diode and a capacitor are connected to a buffer. In the first charging circuit, an overshoot based on a reflected signal generated by an output signal is stored as an electric charge to the capacitor, and in the second charging circuit, an undershoot based on a reflected signal generated by an input signal is charged as an electric charge to the capacitor, whereby the energy of the overshoot and the like is recovered. These charges are collected in the charging circuit, stored in the capacitor, converted into a power supply voltage of an internal power supply by a stabilization circuit, and are supplied as an internal power supply. As a result, the reflected energy of the signal generated during signal transmission at the time of data transfer between semiconductor devices is stored, and the stored energy is used in the driving of the signals, so that the noise generated by reflection is reduced, and the power is efficiently utilized.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The present invention relates to a semiconductor device in which electric power can be efficiently used by storing the reflected energy generated during signal exchange and recovering the stored energy into power supply voltage.  
         [0003]     2. Description of the Related Art  
         [0004]     The frequency of signals handled by semiconductors increases every year in conjunction with the current development of digital technologies, and semiconductor devices for transferring data between semiconductor devices have been implemented by using interfaces having frequencies in excess of 1000 MHz. As the frequency of interface signals becomes higher, an increase in the speed of the rise and fall when these signals are driven is required. However, reducing the rise time and fall time of the signals tends to produce overshooting in which the signal waveform temporarily exceeds the stipulated level because of mismatching of the characteristic impedance of the transmission path, and undershooting in which the signal waveform temporarily falls below the stipulated level. Overshooting and undershooting are accompanied by relatively large currents, but are completely unnecessary for signal propagation, and merely increase the power consumption.  
         [0005]     The technique disclosed in Japanese Laid-open Patent Application No. 8-149831 is known as a technique that allows the excess voltage energy accompanying the switching operation of a power device to be efficiently recovered on the power supply side.  FIG. 1  is a circuit diagram showing the construction of the voltage inverter described in this Japanese Laid-open Patent Application No. 8-149831.  
         [0006]     As is shown in  FIG. 1 , circular-flow diodes  103   a  and  103   b  and snubber circuits  104   a  and  104   b  are connected in-parallel to GTOs (gate turn-off thyristors)  102   a  and  102   b  , respectively. The snubber circuit  104   a  comprises a diode  114   a  and a capacitor  115   a  , and the snubber circuit  104   b  comprises a diode  114   b  and a capacitor  115   b  . Furthermore, a capacitor (energy recovery capacitor)  105  is connected in parallel with the capacitors  115   a  and  115   b  via respective diodes  106   a  and  106   b . Moreover, the GTOs  102   a  and  102   b  are connected to a direct-current power supply  110  via respective reactors  107   a  and  107   b.    
         [0007]     The steep voltage rise occurring when the GTOs  102   a  and  102   b  are off is suppressed by the snubber circuits  104   a  and  104   b ; furthermore, the abrupt current variation occurring when the GTOs  102   a  and  102   b  are on is suppressed by the reactors  107   a  and  107   b . Moreover, the absorbed energy that charges the respective capacitors  115   a  and  115   b  inside the snubber circuits  104   a  and  104   b  charges the capacitor  105  via the diodes  106   a  and  106   b  in accordance with the switching operation of the GTOs  102   a  and  102   b  accompanying the rise in the charging voltage. Furthermore, the capacitor  105  is charged with the absorbed energy of the reactors  107   a  and  107   b  via the diodes  106   a  and  106   b  when the GTOs  102   a  and  102   b  are off.  
         [0008]     The voltage inverter  100  is also provided with a voltage comparator circuit  108  for detecting the charging voltage of the capacitor  105 ; GTOs  111   a  and  11   b , which are switching elements that switch the connection between the capacitor  105  and the direct-current power supply  110  on and off; and ignition circuits  109   a  and  109   b  that control this switching operation. When the charging voltage of the capacitor  105  exceeds the power supply voltage, the capacitor  105  and direct-current power supply  110  are connected by switching the switching elements on, and the charged energy of the capacitor  105  is recovered on the power supply side via the reactors  112   a  and  112   b  and the diode  113 . Furthermore, in  FIG. 1 , the power supply voltage is used as the comparative voltage of the voltage comparator circuit  108 ; however, an embodiment that allows comparison with a specified reference voltage is described in Japanese Laid-open Patent Application No. 8-149831.  
         [0009]     However, the prior art described in Japanese Laid-open Patent Application No. 8-149831 suffers from the following problems.  
         [0010]     In signal transmission via a driver and receiver in a conventional electronic circuit, an increase in the frequency results in an increase in the amount of current that is supplied to the LSI (large scale integrated circuits), so that the consumption of power and generation of heat are increased. Furthermore, such an increase in the amount of heat generated makes it necessary to increase the performance of the cooling system, so that an increase in the size of the heat sink and an increase in the speed of the cooling fan become necessary, resulting in the problem of a deleterious effect on the environment. These problems run counter to the current movement of easing the environmental problems.  
         [0011]     As was described above, when the rise time and fall time during the driving of signals in data transfer between semiconductor devices are shortened, overshooting and undershooting, which constitute noise components, are generated as a result of the mismatching of the characteristic impedance of the transmission path, so that the power consumption is increased. Accordingly, if feedback means for reutilizing power arising from overshooting and undershooting can be provided, this will lead to the efficient utilization of power, and the noise component caused by reflection can be reduced.  
         [0012]     In the past, energy recovery circuits using snubber circuits have been known, as described in Japanese Laid-open Patent Application No. 8-149831. However, such techniques fail to suppress the overshooting and undershooting generated during high-frequency signal transmission between semiconductor devices, or to reduce power consumption by reutilizing reflected energy.  
       SUMMARY OF THE INVENTION  
       [0013]     An object of the present invention is to provide a semiconductor device in which reflection-induced noise can be reduced and electric power can be efficiently used by storing the reflected energy generated during signal transmission in the exchange of data between semiconductor devices, and using the stored energy during driving of the signals.  
         [0014]     The semiconductor device according to the present invention comprises an energy recovery part wherein an overshoot and undershoot during an input or output of a signal in an input buffer or output buffer are recovered as energy, a charging part for charging the recovered energy, and a supply part for supplying an electric charge charged in the charging part as power supply voltage.  
         [0015]     The semiconductor device according to the present invention comprises an output terminal, an output buffer for outputting a signal via the output terminal, a power supply for supplying a voltage to, and operating, an electronic circuit that includes the output buffer, a first circuit which is connected to the output buffer and in which an overshoot whose output voltage exceeds the power supply voltage during the transition of the output signal level is recovered as energy and charged, a second circuit which is connected to the output buffer and in which an undershoot whose output voltage falls below the ground voltage during the transition of the output signal level is recovered as energy and charged, a charging circuit which is connected to the first or second circuit and which collects the charge charged by the first or second circuit, a switch for switching the connection between the first and second circuit and the charging circuit, a capacitor which is connected to the charging circuit and which stores the charge collected by the charging circuit, and a supply circuit which is connected to the abovementioned capacitor and which converts the charge stored in this capacitor into a power supply voltage of an internal power supply, and supplies this voltage as an internal power supply.  
         [0016]     The semiconductor device according to the present invention comprises an input terminal, an input buffer for inputting a signal via the input terminal, a power supply for supplying a voltage to, and operating, an electronic circuit that includes the input buffer, a first circuit which is connected to the input buffer and in which an overshoot whose input voltage exceeds the power supply voltage during the transition of the input signal level is recovered as energy and charged, a second circuit which is connected to the input buffer and in which an undershoot whose input voltage falls below the ground voltage during the transition of the input signal level is recovered as energy and charged, a charging circuit which is connected to the first or second circuit and which collects the charge charged by the first or second circuit, a switch for switching the connection between the first and second circuit and the charging circuit, a capacitor which is connected to the charging circuit and which stores the charge collected by the charging circuit, and a supply circuit which is connected to the abovementioned capacitor and which converts the charge stored in this capacitor into a power supply voltage of an internal power supply, and supplies this voltage as an internal power supply.  
         [0017]     The switch may comprise a field effect transistor.  
         [0018]     The semiconductor device according to the present invention comprises an output terminal; an output buffer for outputting a signal via the output terminal; a power supply for supplying a voltage to, and operating, an electronic circuit that includes the output buffer; a first circuit which is connected to the output buffer and in which an overshoot whose output voltage exceeds the power supply voltage during the transition of the output signal level is recovered as energy and charged; a second circuit which is connected to the output buffer and in which an undershoot whose output voltage falls below the ground voltage during the transition of the output signal level is recovered as energy and charged; charging circuits which are separately connected to the first and second circuits, and which collect the charge charged by the first and second circuits; capacitors which are connected in a corresponding manner to the charging circuits and which store the charge collected by the charging circuits; and supply circuits which are separately connected to the capacitors and which convert the charge stored in the capacitors into a power supply voltage of an internal power supply, and supply the voltage as an internal power supply.  
         [0019]     The semiconductor device according to the present invention comprises an input terminal; an input buffer for inputting a signal via the input terminal; a power supply for supplying a voltage to, and operating, an electronic circuit that includes the input buffer; a first circuit which is connected to the input buffer and in which an overshoot whose input voltage exceeds the power supply voltage during the transition of the input signal level is recovered as energy and charged; a second circuit which is connected to the input buffer and in which an undershoot whose input voltage falls below the ground voltage during the transition of the input signal level is recovered as energy and charged; charging circuits which are separately connected to the first and second circuits, and which collect the charge charged by the first and second circuits; capacitors which are connected in a corresponding manner to the charging circuits and which store the charge collected by the charging circuits; and supply circuits which are separately connected to the capacitors and which convert the charge stored in the capacitors into a power supply voltage of an internal power supply, and supply the voltage as an internal power supply.  
         [0020]     The first and second circuits can be configured so that snubber circuits constructed by connecting a diode and a capacitor in series are included.  
         [0021]     A configuration can be adopted in which the first circuit has a first diode whose cathode side is connected to the input or output buffer and whose anode side is connected to the power supply, a second diode which is connected to the connection point between the first diode and the input or output buffer and whose anode side is connected to this connection point, a first capacitor which is connected to the second diode, and a first switch for switching the first capacitor to the ground point or the connection point between the power supply and the first diode; the connection point between the second diode and the first capacitor is connected to the charging circuit via the switch; the second circuit has a third diode whose anode side is connected to the input or output buffer and whose cathode side is connected to the ground point, a fourth diode which is connected to the connection point between the third diode and the ground point and whose anode side is connected to this connection point, a second capacitor which is connected to the fourth diode, and a second switch for switching the second capacitor to the ground point or the connection point between the input or output buffer and the third diode; and the connection point between the fourth diode and the second capacitor is connected to the charging circuit via the switch.  
         [0022]     The first and second switches may comprise field effect transistors.  
         [0023]     A configuration may be adopted in which the first circuit has a first diode whose cathode side is connected to the input or output buffer and whose anode side is connected to the power supply, a second diode which is connected to the connection point between the first diode and the input or output buffer and whose anode side is connected to this connection point, and a first capacitor one end of which is connected to the second diode and the other end of which is grounded; the connection point between the second diode and the first capacitor is connected to the charging circuit; the second circuit has a third diode whose anode side is connected to the input or output buffer and whose cathode side is connected to the ground point, a fourth diode which is connected to the connection point between the third diode and the ground point and whose anode side is connected to this connection point, and a second capacitor one end of which is connected to the fourth diode and the other end of which is grounded; and the connection point between the fourth diode and the second capacitor is connected to the charging circuit.  
         [0024]     In the present invention, the reflected energy of the signals generated in cases where electrical signals are transmitted to signal lines in electronic circuits is stored, and the stored energy is used when the drivers drive the signal lines, so that the noise generated by reflection is reduced, and the energy can be effectively utilized, thus reducing the amount of power consumption. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0025]      FIG. 1  is a circuit diagram showing the structure of the voltage inverter described in Japanese Laid-open Patent Application No. 8-149831;  
         [0026]      FIG. 2  is a circuit diagram showing the structure of a semiconductor device according to a first embodiment of the present invention;  
         [0027]      FIG. 3  is a perspective view showing the external appearance of a semiconductor device according to a first embodiment of the present invention;  
         [0028]      FIG. 4  is a circuit diagram showing the structure of a semiconductor device according to a second embodiment of the present invention;  
         [0029]      FIG. 5  is a circuit diagram showing the structure of a semiconductor device according to a third embodiment of the present invention; and  
         [0030]      FIG. 6  is a circuit diagram showing the structure of a semiconductor device according to a fourth embodiment of the present invention. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0031]     Embodiments of the present invention will now be described in specific terms with reference to the accompanying drawings. First, a first embodiment of the present invention will be described.  FIG. 2  is a circuit diagram showing the structure of a semiconductor device according to a first embodiment of the present invention. Furthermore,  FIG. 3  is a perspective view showing the external appearance of the semiconductor device of this embodiment.  
         [0032]     As is shown in  FIG. 2 , the semiconductor device of the present embodiment comprises a buffer  1  that constitutes the final stage of an output buffer. The buffer  1  outputs an output signal  6  corresponding to an input signal  5 . When the input level varies from a high level to a low level, the output level varies from a low level to a high level. Conversely, when the input level varies from a low level to a high level, the output level varies from a high level to a low level.  
         [0033]     The buffer  1  is connected to a charging circuit  2  comprising a diode  21 , a diode  22 , a capacitor  23 , and a switch  24 . The buffer  1  is connected to an IO power supply via the diode  21 , and the anode side of the diode  21  is the power supply side. Furthermore, the connection point between the diode  21  and the buffer  1  is connected to the diode  22 , the diode  22  is connected to the capacitor  23 , and the capacitor  23  is connected to the switch  24 . Moreover, the cathode side of the diode  22  is the side of the capacitor  23 . Furthermore, by switching the connection of the switch  24 , the capacitor  23  is either connected to the connection point between the IO power supply and the diode  21 , or grounded.  
         [0034]     Furthermore, the buffer  1  is connected to a charging circuit  3  comprising a diode  31 , a diode  32 , a capacitor  33 , and a switch  34 . The buffer  1  is grounded via the diode  31 , and the cathode side of the diode  31  is the ground side. Furthermore, the connection point between the diode  31  and the ground point is connected to the diode  32 , the diode  32  is connected to the capacitor  33 , and the capacitor  33  is connected to the switch  34 . Moreover, the cathode side of the diode  32  is the side of the capacitor  33 . Furthermore, by switching the connection of the switch  34 , the capacitor  33  is either connected to the connection point between the buffer  1  and diode  31 , or grounded.  
         [0035]     The connection point between the diode  22  and capacitor  23 , and the connection point between the diode  32  and capacitor  33  are both connected to a charging circuit  41  via the switching of a switch  7 . Furthermore, the charging circuit  41  collects the charge that is temporarily stored in the capacitor  23  or  33 . Moreover, the charging circuit  41  is connected to a capacitor  42 , and the charge collected by the charging circuit  41  is stored in the capacitor  42 . Furthermore, in order to convert the charge stored in the capacitor  42  to the power supply level of the internal power supply, the capacitor  42  is connected to a stabilization circuit  43 . For example, the switches  24 ,  34  and  7  are constructed from FETs (field effect transistors), and are switched according to the output level or input level.  
         [0036]     Next, the operation of the present embodiment will be described. First, as is shown in  FIG. 2 , the switch  24  is connected to the IO power supply and the anode side of the diode  21 , the switch  34  is connected to the GND (ground) side, and the switch  7  is connected to the charging circuit  3 . When the input signal  5  varies from a high level to a low level, the buffer  1  performs the opposite action from the input level; accordingly, the output level varies from a low level to a high level. The output side of the buffer  1  is generally connected to a receiver, so that a reflected wave returns as a result of mismatching of the characteristic impedance; this reflected wave may exceed the power supply voltage of the buffer  1 . In the present invention, the voltage is recovered in cases where the voltage of the output signal  6  exceeds the power supply voltage of the buffer  1  as a result of reflection. Specifically, when the voltage of the signal appearing at the output exceeds the power supply voltage, a current flows through the diode  22 , so that a charge is accumulated in the capacitor  23 .  
         [0037]     Next, when the input signal  5  varies from a low level to a high level, the buffer  1  performs the opposite action from the input level, so that the output level varies from a high level to a low level. In this case, the switch  24  is connected to the GND side, the switch  34  is connected to the buffer  1  and the anode side of the diode  31 , and the switch  7  is connected to the charging circuit  2 . When the output level varies from a high level to a low level, there may be cases in which a voltage equal to or less than the GND level is generated in the output level as a result of reflection. When the voltage of the signal appearing at the output falls to or below the GND level, a current flows through the diode  32 , so that a charge is accumulated in the capacitor  33 . Meanwhile, the charge stored in the capacitor  33  moves to the charging circuit  41  via the switch  7 .  
         [0038]     Furthermore, when the input voltage of the input signal  5  again varies from a high level to a low level, the level of the output signal  6  varies from a low level to a high level. In this case, the switch  24  is connected to the power supply and the anode side of the diode  21 , the switch  34  is connected to the GND side, and the switch  7  is connected to the charging circuit  3 . As a result, the charge stored in the capacitor  33  moves to the charging circuit  41  via the switch  7 .  
         [0039]     Thus, as a result of the charges generated by reflection being collected in the capacitors  23  and  33 , there is no subsequent reflection by the buffer  1 .  
         [0040]     The capacitor  42  is charged with the charges collected in the charging circuit  41 . The charge stored in the capacitor  42  is supplied as an internal power supply after the voltage is converted to the power supply voltage of this internal power supply by the stabilization circuit  43 .  
         [0041]     Next, the external appearance of the present embodiment will be described with reference to  FIG. 3 . In  FIG. 3 , a capacitor  51  is disposed on an interposer  50  that accommodates the semiconductor, and a heat sink  52  is disposed on top of this. Heat generated in the interior of the device is transmitted to the interposer  50 . The heat is further transmitted to the heat sink  52  via the capacitor  51 , and is dissipated into the atmosphere. The capacitor  51  includes the capacitor  42  shown in  FIG. 2 . This capacitor stores the charge collected by the charging circuit  41  and supplies power to the stabilization circuit  43 .  
         [0042]     Next, the effect of the present embodiment will be described.  
         [0043]     The first effect is that the power consumption of a system using the semiconductor device according to the present invention can be reduced by making it possible to reutilize the power of noise components such as overshooting, undershooting, and the like generated by reflection during signal transfer.  
         [0044]     The second effect is that noise generated by reflection can be reduced by absorbing the power of overshooting and undershooting.  
         [0045]     The third effect is that the signal level can be stabilized by reducing noise, so that the possibility of being able to utilize much higher frequencies is increased. Furthermore, this means that operation at such frequencies can be stabilized.  
         [0046]     The fourth effect is that the return of current generated by overshooting and undershooting to the power supply can be eliminated, so that the level of electromagnetic field emissions from the power supply lines can be lowered.  
         [0047]     Next, a second embodiment of the present invention will be described.  FIG. 4  is a circuit diagram showing the structure of a semiconductor device according to a second embodiment of the present invention.  
         [0048]     In  FIG. 4 , a charging circuit  44 , a capacitor  45  and a stabilization circuit  46  are provided in the structure shown in  FIG. 2 . Meanwhile, the switches  24 ,  34 , and  7  are not installed, the capacitors  23  and  33  are grounded to GND, and the charging circuits  2  and  3  are respectively connected to the charging circuits  44  and  41 . The remaining structure is the same as in  FIG. 2 . Accordingly, constituent elements that are the same as in  FIG. 2  are labeled with the same symbols, and a detailed description of these elements is omitted.  
         [0049]     Next, the operation of this embodiment will be described. The buffer  1  drives an output signal  6  in accordance with the level of the input signal  5 . When the input signal  5  varies from a high level to a low level, the buffer  1  performs the opposite action from the input level; accordingly, the output level varies from a low level to a high level. The output signal  6  output from the buffer  1  is generally connected to a receiver, so that a reflected wave returns as a result of mismatching of the characteristic impedance. Furthermore, the reflected wave may exceed the power supply voltage of the buffer  1 . In the present invention, in cases where the voltage of the output signal  6  exceeds the power supply voltage of the buffer  1  as a result of reflection, this is recovered as a charge. Specifically, when the voltage of a signal appearing at the output exceeds the power supply voltage, a current flows through the diode  22 , so that the capacitor  23  is charged. The charge collected by the capacitor  23  is stored in the capacitor  45  by the charging circuit  44 . The charge stored in the capacitor  45  is converted to the power supply voltage of an internal power supply by the stabilization circuit  46 , and is supplied as an internal power supply.  
         [0050]     Next, when the input signal  5  varies from a low level to a high level, the output signal  6  varies from a high level to a low level. When the output signal  6  varies from a high level to a low level, a voltage equal to or less than the GND level is generated by reflection at the output pin. When the output falls to or below the GND level, a current flows through the diode  32 , so that the capacitor  33  is charged. The charge with which the capacitor  33  is charged is caused to charge the capacitor  42  by the charging circuit  41 . The charge with which the capacitor  42  is charged is supplied as an internal power supply after the voltage is converted to the power supply voltage of this internal power supply by the stabilization circuit  43 .  
         [0051]     Thus, the charge generated by reflection is collected in the capacitors  23  and  33 , so that there is no subsequent reflection by the buffer  1 .  
         [0052]     Furthermore, the effects of this embodiment are the same as those of the first embodiment.  
         [0053]     Next, a third embodiment of the present invention will be described.  FIG. 5  is a circuit diagram showing the structure of a semiconductor device according to a third embodiment of the present invention. In  FIG. 5 , the buffer  1 , which is the driver in  FIG. 4 , is replaced by a receiver  8 , and an input signal  9  is input into the receiver  8 . The remaining structure is the same as in  FIG. 4 . Accordingly, constituent elements that are the same as in  FIG. 4  are labeled with the same symbols, and a detailed description of these elements is omitted.  
         [0054]     Next, the operation of this embodiment will be described. The operation of the present embodiment is similar to the operation of the second embodiment. The current caused by a voltage exceeding the power supply voltage, and the current caused by a voltage equal to or less than the GND level due to overshooting and undershooting are collected and used as an internal power supply.  
         [0055]     Specifically, when the voltage of the signal input into the receiver  8  exceeds the power supply voltage, electric current flows through the diode  22 , and the current is accumulated in the capacitor  23 . The charge collected by the capacitor  23  is stored in the capacitor  45  by the charging circuit  44 . Furthermore, the charge stored in the capacitor  45  is supplied as an internal power supply after the voltage is converted into the power supply voltage of this internal power supply by the stabilization circuit  46 . On the other hand, when the voltage of the input signal  9  falls to or below the GND level, an electric current flows through the diode  32 , and is stored in the capacitor  33 . The charge collected by the capacitor  33  is stored in the capacitor  42  by the charging circuit  41 . Furthermore, the charge stored in the capacitor  42  is supplied as an internal power supply after the voltage is converted to the power supply voltage of this internal power supply by the stabilization circuit  43 .  
         [0056]     Thus, reflection is reduced as a result of the charges generated by overshooting and undershooting being collected in the capacitors  23  and  33 . Furthermore, the effects of the present embodiment are the same as those of the first embodiment.  
         [0057]     Next, a fourth embodiment of the present invention will be described.  FIG. 6  is a circuit diagram showing the structure of a semiconductor device according to a fourth embodiment. In  FIG. 6 , the buffer  1 , which is the driver in  FIG. 2 , is replaced by a receiver  8 , and an input signal  9  is input into this receiver  8 . The remaining structure is the same as in  FIG. 2 . Accordingly, constituent elements that are the same as in  FIG. 2  are labeled with the same symbols, and a detailed description of these elements is omitted. The operation of the present embodiment is also the same as the operation of the first embodiment, and the effects of the present embodiment are the same as those of the first embodiment.  
         [0058]     The present invention is suitable for use in semiconductor devices built into information devices, communications devices, video devices, and other devices having numerous signal lines and requiring the high-speed transmission of signals.