Classifications

• • H—ELECTRICITY
  • H03—ELECTRONIC CIRCUITRY
  • H03K—PULSE TECHNIQUE
  • H03K19/00—Logic circuits, i.e. having at least two inputs acting on one output; Inverting circuits
  • H03K19/01—Modifications for accelerating switching

Definitions

• This invention relates generally to enabling circuitry for logic circuits and, more particularly, to enabling circuitry for transistor-transistor logic (TTL) circuitry which utilizes the clock signal directly rather than after inversion to reduce the enabling delay without an associated power penalty.
• TTL transistor-transistor logic
• Logic circuits such as data latches, flip-flops, shift registers, memories, etc. may require that an enabling signal be applied thereto in order to render the logic circuit operational.
• an enabling signal For example, the ALS377 hex data latch manufactured by Motorola Inc. requires the presence of such a signal.
• Prior art enabling circuitry requires that an external clock signal (CK) propagate through three gates before the required enabling signal is produced. Thus, the enabling of the particular logic circuit involved is delayed by the propagation delay of the three gates. If the clock signal could be used directly rather than requiring inversion in the first of the three gates, there could be a significant improvement in enabling time.
• a logic circuit having at least first and second inputs and capable of assuming first and second stable states at an output node thereof when said output node is coupled to a load, said first and second stable states corresponding to logical high and logical low voltages, said output node exhibiting said logical high voltage only when said first input is coupled to said logical high voltage and said second input is coupled to said logical low voltage, comprising: first buffer means having an input coupled to said first input and responsive to the voltage thereon; first transistor means having base, emitter and collector terminals, said base coupled to an output of said first buffer means for controlling said first transistor means, said collector adapted to be coupled to a first source of supply voltage, and said emitter coupled to said output node, said first transistor means for supplying current to said output node only when said first input is coupled to said logical high voltage; second buffer means coupled to said second input; and second
• CM According to a further aspect of the invention there is a circuit for generating an internal enabling signal from an external clock signal and an external enabling signal each capable of assuming high and low logic states, comprising: a first logic gate having a first input coupled to receive said external clock signal and a second input coupled to receive said internal enabling signal for generating a logical high output when said external clock signal is a logical high and said internal enabling signal is a logical low; and second logic means having a first input coupled to the output of said first logic gate and a second input coupled to receive said external enabling signal for generating said internal enabling signal.
• FIG. 1 is a logic diagram of enabling circuitry in accordance with the prior art
• FIG. 2 is a logic diagram of enabling circuitry in accordance with the present invention
• FIG. 3 is a partial logic, partial schematic diagram of the inventive enabling circuitry.
• FIG. 1 is a block diagram of circuitry for enabling a logic circuit 8 in accordance with the prior art.
• logic circuit 8 may take a variety of forms; i.e., shift registers, data latches, memories, etc.
• two inputs are provided to logic circuit 8.
• the first occurring on line 10 is the inverted clock signal C which is produced at the output of inverter 2.
• the second input appears on line 12 and is the actual enable signal (ENABLE) produced by the enabling circuitry and appearing at the output of NOR gate 4.
• the clock signal CK is applied to the input of an inverter 2 the output of which is coupled to an input of NOR gate 6.
• the actual enable signal (ENABLE) is applied to a second input of NOR gate 6 whose output is applied to a first input of NOR gate 4.
• An external enable signal (EN) is applied to a second input of NOR gate 4.
• the external enable signal EN is assumed to be in a low logic state initially.
• the clock signal CK goes low at the input of inverter 2
• a logical high is applied to a first input of NOR gate 6. Since a NOR gate exhibits a high output only if both inputs are low, the output of NOR gate 6 ,will be low. Since the external enable signal EN is also low, a logical high will be produced at the output of NOR gate 4 to enable logic circuit 8.
• FIG. 2 is a logic diagram of the inventive enabling circuitry.
• the clock signal CK is still applied to an input of inverter 2 the output of which (CK) is applied to logic circuit 8.
• the external enable signal EN is still applied to a first input of NOR gate 4 the output of which represents the actual logic circuit enable signal (ENABLE) on line 12.
• the significant differences are that the clock signal CK is applied directly to a first input of AB gate.
• the second input of gate 16 is coupled via line 14 to the output of NOR gate
• FIG. 1 the output of NOR gate 6 takes the form A B if signals A and B are supplied to the first and second inputs thereof. Therefore, the actual output of NOR gate 6 in FIG. 1 is CK ENABLE.
• the output of gate 16 in FIGURE 2 takes the form AB " if A is applied to the non-inverting input and. B is applied to the inverting input. Thus, the actual output of AB gate 16 is CK ENABLE. Since the outputs of NOR gate 6 in FIG.
• FIG. 3 illustrates the details of AB " gate 16 of FIG. 2. It includes PNP transistor 18, Schottky transistors 20 and 22, diode 24, Schottky diodes 26 and 28 and resistors 30, 32 and 34. The base of transistor 18 and the cathode of diode 26 are directly coupled to the clock signal CK. The collector of transistor 18 and the cathode of diode 24 are coupled to ground. The emitter of
• O transistor 18 is coupled to a source of supply voltage V ⁇ C via resistor 30 and to the base of transistor 20.
• the collector of transistor 20 is coupled to the source of supply voltage V QQ via resistor 32, and the emitter of transistor 20 is coupled to the collector of transistor 22, to the anode of diode 26, and to the second input of NOR gate 4.
• the emitter of transistor 22 is coupled to the anode of diode 24.
• the base of transistor 22 is coupled to the source of supply voltage V QQ via resistor 34 and to the anode of diode 28.
• Schottky diode 26 provides a discharge path for the parasitic capacitance associated with the base-emitter junction of transistor 20 when the clock signal CK is low.
• the AB function (CK ENABLE) actually appears at node 36. That is, when the clock signal (CK) is high, transistor 18 remains off and transistor 20 is turned on. Current then flows from V QQ through resistor 32 into node 36. If ENABLE is low, current flows from V cc through resistor 34 and through diode 28. Base drive is not supplied to transistor 22 maintaining it off. Since transistor 22 is off, it sinks no current from node 36 and therefore the voltage at node 36 rises to a logical high level. All other combinations of CK and ENABLE will result in a logical zero at node 36. That is, it has already been shown that when the clock signal CK is high, current flows into node 36.
• transistors and/or diodes could be add ⁇ d to increase the number of asserted or inverted inputs to the gate to expand its functionality.

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• Physics & Mathematics (AREA)
• Engineering & Computer Science (AREA)
• Computer Hardware Design (AREA)
• Computing Systems (AREA)
• General Engineering & Computer Science (AREA)
• Mathematical Physics (AREA)
• Logic Circuits (AREA)

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Citations (6)

• 1981
  • 1981-06-19 US US06/275,530 patent/US4398103A/en not_active Expired - Fee Related
• 1982
  • 1982-05-06 JP JP57501822A patent/JPS58500965A/ja active Granted
  • 1982-05-06 WO PCT/US1982/000598 patent/WO1982004510A1/en not_active Application Discontinuation
  • 1982-05-06 EP EP19820901819 patent/EP0082851A4/de not_active Ceased

Patent Citations (6)

Non-Patent Citations (2)

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