One stage word line decoder/driver with speed-up Darlington drive and adjustable pull down

• US 5,255,240 A
• Filed: 06/13/1991
• Issued: 10/19/1993
• Est. Priority Date: 06/13/1991
• Status: Expired due to Fees

• Current Assignee: International Business Machines Corporation
• Original Assignee: International Business Machines Corporation
• Inventors: Wong, Robert C.
• Primary Examiner(s): Callahan, Timothy P.
• Application Number:
  US07/714,442
• Time in Patent Office: 859 Days
• Field of Search: 365/230.06, 365/189, 365/189.06, 365/174, 307/270, 307/315, 307/443
• US Class Current: 365/230.06
• CPC Class Codes: G11C 8/08 Word line control circuits, e.g. drivers, boosters, pull-up circuits, pull-down circuits, precharging circuits, for word lines
• CPC Class Codes: G11C 8/10 Decoders
• CPC Class Codes: H03K 19/0133 by bootstrapping, i.e. by positive feed-back
• CPC Class Codes: H03K 19/0136 by means of a pull-up or down element

Abstract

A word line decoder/driver has a Darlington circuit connected in parallel with word line driver transistors to provide rapid switching thereof. The Darlington circuit receives an input from decoder transistors through a capacitance, such as a diffusion capacitance, which establishes a time constant longer than the nominal access cycle time of the memory. Thus, during the nominal cycle time of the memory, the word line driver transistors merely supplement the pull-up of the word lines, the speed of which is limited only by the switching speed of the Darlington circuit. Therefore, the pull-up of the input to the word line driver transistors is made non-critical and the circuit can be simplified to reduce element count while achieving substantial reduction in power consumption. While the fast collector pull down of the deselected word line is controlled by an adjustable clamp, word line pull-up is maintained well below 1 nsec and chip access time is below 2 nsec and voltage margins are increased. By converting input voltage levels to lower values with respect to the power supply voltage, large voltage swings can be achieved with a single stage circuit within a 3.6 volt power supply.

Claims

1. A word line driver circuit for a memory means, said word line driver circuit having at least one word line driver transistor including

a Darlington circuit connected in parallel with said at least one word line driver transistor;

an input to said Darlington circuit being connected to an input of said word line driver transistor through a bootstrap capacitor.

2. A circuit as recited in claim 1, wherein said bootstrap capacitor is provided with a conductance means;

the combination of said capacitor and said conductance forming a time constant producing means.

3. A circuit as recited in claim 2, wherein said time constant producing means includes a diffusion capacitance.

4. A circuit as recited in claim 3, wherein a time constant produced by said time constant producing means is in excess of an access cycle time of said memory means.

5. A word line driver circuit for a memory means, said word line driver circuit having at least one word line driver transistor including

a Darlington circuit connected in parallel with said at least one word line driver transistor;

an input to said Darlington circuit being connected to an input of said word line driver transistor through a bootstrap capacitor having a capacitance which is variable with a conductance through said bootstrap capacitor.

6. A circuit as recited in claim 5, wherein said bootstrap capacitor is provided with a conductance means;

the combination of said capacitor and said conductance forming a time constant producing means.

7. A circuit as recited in claim 6, wherein said time constant producing means is a diffusion capacitance.

8. A circuit as recited in claim 7, wherein a time constant produced by said time constant producing means is in excess of an access cycle time of said memory means.

9. A circuit as recited in claim 5, wherein said capacitance is a diffusion capacitance.

10. A word line decoder/driver circuit for a memory device including a half current switch, said half current switch including an adjustable clamp means for clamping a down-level voltage of a drain line of said memory device.

11. A circuit as recited in claim 10, wherein said adjustable clamp means includes means for providing temperature compensation of said half current switch.

12. A circuit as recited in claim 11, wherein said half current switch includes a transistor and wherein said means for providing temperature compensation of said half current switch comprises a feedback circuit connected to conduct current away from a base of said transistor of said half current switch.