Abstract:
A pulse-controlled analog flip-flop includes a charge element; a charge storage element connected to the charge element; an element for detecting the voltage across the storage element; and an element for discharging the storage element when the detection element has detected that the voltage across the storage element has reached a predetermined threshold.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to a pulse-controlled analog flip-flop, that is, a circuit having an output state which is one or the other of two voltage states and is controlled by a series of pulses, one or several pulses switching the flip-flop from a first state to a second state and an additional pulse making the flip-flop return from the second state to the first state. 
     Such a flip-flop can, for example, be used to control the gate of a MOS transistor, the first state corresponding to a voltage level adapted to turn on this MOS transistor and the other state corresponding to a voltage level adapted to turn off (make non-conductive) the MOS transistor. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to provide such a flip-flop which is of particularly simple structure. 
     Another object of the present invention is to provide such a flip-flop capable of providing high voltage levels. 
     Another object of the present invention is to provide such a flip-flop which is controllable either by a succession of positive pulses or by a succession of negative pulses. 
     Another object of the present invention is to provide such a flip-flop which can be simply modified to provide a positive or negative output voltage level. 
     To achieve these objects as well as others, the present invention provides a pulse-controlled analog flip-flop including a charge means; a charge storage means connected to the charge means; a means for detecting the voltage across the storage means; and a means for discharging the storage means when the detection means has detected that the voltage across the storage means has reached a predetermined threshold. 
     According to an embodiment of the present invention, the storage means includes a capacitor. 
     According to an embodiment of the present invention, the discharge means includes a thyristor. 
     According to an embodiment of the present invention, the detection means includes a Zener diode. 
     According to an embodiment of the present invention, the charge means includes a capacitor in series with a first diode between a first input terminal and a first terminal of the storage means, and a second diode connected between the connection point of said capacitor and of the first diode and a second supply terminal connected to the second terminal of the storage means. 
     According to an embodiment of the present invention, the analog flip-flop includes two input terminals; two output terminals; a first storage capacitor connected to the output terminals; a charge circuit, connected between the input terminals and the first capacitor, including a second capacitor connected to an input terminal in series with a first diode connected to the first terminal of the first capacitor, and a second diode connected between the connection point of the second capacitor and of the first diode and the second terminal of the first capacitor, and connected to the second input terminal; a thyristor connected across the capacitor; and a Zener diode connected between the thyristor gate and a terminal representative of the voltage across the capacitor. 
     According to an embodiment of the present invention, the Zener diode is connected to the connection point between the second capacitor and the first diode. 
     The foregoing objects, features and advantages of the present invention, will be discussed in detail in the following non-limiting description of specific embodiments in connection with the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 shows a first embodiment of the present invention; 
     FIG. 2A shows a succession of pulses that can be applied to a flip-flop such as that in FIG. 1; 
     FIG. 2B shows the output voltage of a flip-flop such as that in FIG. 1 receiving the pulses illustrated in FIG. 2A; and 
     FIG. 3 shows an alternative embodiment of the flip-flop according to the present invention. 
    
    
     DETAILED DESCRIPTION 
     The circuit of FIG. 1 includes a charge accumulation or voltage storage means shown in the form of a capacitor C. Capacitor C is connected to input terminals  1  and  2  via a charge circuit  4 . The output of capacitor C is connected to output terminals  6  and  7 . Terminal  7  is directly connected to terminal  2  and forms, for example, a ground terminal. A discharge means formed, for example, of a cathode-gate thyristor Th 1  is connected across capacitor C. A means for detecting the voltage across capacitor C is also provided. 
     In the embodiment shown, charge circuit  4  includes a capacitor C 1 , a first terminal of which is connected to input terminal  1  and the second terminal of which is connected to the anode of a diode D 1 . The cathode of diode D 1  is connected to the first terminal of capacitor C. Connection point  5  of capacitor C 1  and of diode D 1  is connected via a diode D 2  to second input terminal  2  and to the second terminal of capacitor C, the anode of diode D 2  being on the side of second input terminal  2 . 
     In FIG. 1, the detection means is formed of a Zener diode Z 1 , having its anode connected to the gate terminal of thyristor Th 1  and its cathode connected to interconnection point  5 . 
     The operation of the circuit of FIG. 1 will be described in relation with FIGS. 2A and 2B. 
     At a time t 0  at which the rising edge of a pulse appears between terminals  1  and  2 , voltage V 0  of this pulse is distributed between capacitors C 1  and C. If C 1  and C have identical values, and calling Vbe the forward voltage drop of diode D 1 , voltage VOUT across capacitor C will be: 
     
       
           V   OUT =½( V   0   −V be). 
       
     
     At time t 1  when the pulse ends, capacitor C 1  discharges through diode D 2  while capacitor C remains charged, due to the presence of diode D 1 . 
     At the next pulse, at time t 2 , the charge across capacitor C increases and more specifically tends toward: 
     
       
           V   OUT =¾( V in −V be). 
       
     
     Thus, in the absence of the detection and discharge circuit, the charge across capacitor C a would tend to increase upon each pulse toward an asymptotic value equal to V 0 −Vbe. However, when the voltage across capacitor C reaches a threshold voltage VT that depends on avalanche voltage VZ 1  of diode Z 1  (VT=VZ 1 −2Vbe, assuming that there is a voltage drop Vbe across diode D 2  and a voltage drop Vbe between the thyristor gate and cathode), thyristor Th 1  turns on and remains on as long as the current flowing therethrough is greater than its threshold. Thus, capacitor C discharges substantially completely. Threshold voltage VT is preferably chosen as in the example shown so that the thyristor turns on from the second pulse, at time t 2 . Then, upon each following pulse, it will be alternately switched between a high state and a low state, as shown in FIG. 2B. A pulse-controlled flip-flop has thus been simply obtained. 
     It should be noted that the above circuit is likely to have many alternatives. 
     A three-state device can be obtained by choosing the threshold of the Zener diode so that voltage VT is greater than the voltage reached at time t 2 . Then, at the second pulse, it is switched from a first high state to a second higher high state before falling back to a low state at the third pulse. 
     Any incremental charge means, other than the specific circuit including elements C 1 , D 1 , and D 2 , may be chosen to accumulate charges in capacitor C upon each occurrence of a pulse. Those skilled in the art may be inspired by various existing charge pump or voltage multiplier circuits. 
     A current limiting means may be inserted in the switching branch. 
     The discharge means may be any circuit ensuring the function implemented by thyristor Th 1 , that is, a switching circuit capable of switching to a conduction state when receiving a pulse and to remain in this conduction state until the current or the voltage thereacross has fallen under a low threshold. 
     Finally, the means for detecting the voltage across the capacitor may be any means more sophisticated than Zener diode Z 1 . Further, Zener diode Z 1  has been shown as connected to terminal  5  rather than to output terminal  6 . A connection to output terminal  6  would also be possible, but this would require using a Zener diode of very good quality having a low leakage resistance, to avoid that capacitor C discharges between two pulses. 
     It should be noted that the circuit of FIG. 1 may be controlled by a succession of negative pulses as well as by a succession of positive pulses. In the case of negative pulses, capacitor C will charge upon each rising edge of a pulse (the second edge of the pulse) and the switching from one state to the next one will occur at the rising edge of the next pulse (the second edge of this pulse). Thus, as previously, the first pulse (or more exactly, the second edge of this first pulse) sets terminal  6  to a high level and the second pulse sets it back to a low level. 
     FIG. 3 shows an alternative of the circuit of the present invention in which the same elements have been designated with same references. The polarities of diodes D 1  and D 2 , as well as the polarities of the thyristor and of the Zener diode, are inverted with respect to those of FIG.  1 . These elements are designated by the same references as in FIG. 1 with a prime. Thyristor Th 1 ′ is an anode-gate thyristor. This circuit operates as the preceding one, except that terminal  6  switches, with respect to terminal  7 , from a substantially zero value to a negative value. 
     Thus, the present invention enables controlling any type of MOS transistor or other voltage-controlled component requiring a positive voltage or a negative voltage for its control. 
     Further, as seen previously, this circuit can be simply controlled by positive or negative pulses. 
     Another advantage of the flip-flop according to the present invention is that no auxiliary power supply is required for its operation. 
     Of course, the present invention is likely to have various alterations, modifications, and improvements which will readily occur to those skilled in the art. Such alterations, modifications, and improvements are intended to be part of this disclosure, and are intended to be within the spirit and the scope of the present invention. Accordingly, the foregoing description is by way of example only and is not intended to be limiting. The present invention is limited only as defined in the following claims and the equivalents thereto.