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US 8,035,413 B2Granted
Dynamic impedance control for input/output buffers
AssigneeMosaid Technologies Incorporated
InventorBruce Millar
Life of this patent
Estimating the term…
Abstract
A system and method of performing off chip drive (OCD) and on-die termination (ODT) are provided. A common pull-up network composed of transistors and a common pull-down network composed of transistors are employed to implement both of these functions. In drive mode, the pull-up network is configured to produce a calibrated drive impedance when an “on” output is to be generated, and the pull-up network is configured to produce a calibrated drive impedance when an “off” output is to be generated. In termination mode, the pull-up network and the pull-down network are configured to produce a calibrated pull-up resistance and pull-down resistance respectively such that together, they form a split termination.
Claims34
An apparatus comprising:
- a first combined drive and termination circuit configured to operate with a first supply voltage, the first combined drive and termination circuit comprising:
- a variable impedance pull-up network;
- a variable impedance pull-down network;
- at least one control input for setting a configuration of the pull-up network;
- and
- at least one control input for setting a configuration of the pull-down network;
- a controller that controls calibration being performed in four steps:
- 1) pull-up network calibration for drive mode when a data output is logic high;
- 2) pull-down network calibration for drive mode when a data output is logic low;
- 3) pull-up network calibration for termination mode;
- and
- 4) pull-down network calibration for termination mode;
- and
- a replica of at least part of the combined drive and termination circuit for use in performing calibration;
- the apparatus having a termination mode of operation in which the variable impedance pull-up network is configured to have a pull-up network termination impedance and the variable impedance pull-down network is configured to have a pull-down network termination impedance, the pull-up network and the pull-down network in combination functioning as a split termination;
- the apparatus having a drive mode of operation in which:
- to drive a high output, the pull-up network is configured to generate a specific impedance when switched ON;
- to drive a low output, the pull-down network is configured to generate a specific impedance when switched ON;
- each of the pull-up network and the pull-down network having a plurality of transistors sized to provide identical impedances, and
- each of the pull-up network and the pull-down network being configured to have a desired impedance by progressively varying the number of switched ON transistors.
17 more elements
An apparatus comprising:
- a first combined drive and termination circuit configured to operate with a first supply voltage, the first combined drive and termination circuit comprising:
- a variable impedance pull-up network;
- a variable impedance pull-down network;
- at least one control input for setting a configuration of the pull-up network;
- and
- at least one control input for setting a configuration of the pull-down network;
- and
- a replica of at least part of the combined drive and termination circuit for use in performing calibration;
- the pull-up network and the pull-down network being each formed entirely of P-type transistors or N-type transistors, the apparatus further comprising:
- a controller that controls calibration being performed in two steps:
- 1) pull-up network calibration for drive mode when a data output is logic high;
- and
- 2) pull-up network calibration for termination mode;
- the apparatus having a termination mode of operation in which the variable impedance pull-up network is configured to have a termination impedance and the variable impedance pull-down network is configured to have a pull-down network termination impedance, the pull-up network and the pull-down network in combination functioning as a split termination;
- the apparatus having a drive mode of operation in which:
- to drive a high output, the pull-up network is configured to generate a specific impedance when switched ON;
- and
- to drive a low output, the pull-down network is configured to generate a specific impedance when switched ON;
- each of the pull-up network and the pull-down network having a plurality of transistors sized to provide identical impedances, and
- each of the pull-up network and the pull-down network being configured to have a desired impedance by progressively varying the number of switched ON transistors.
17 more elements
An apparatus comprising:
- a first combined drive and termination circuit configured to operate with a first supply voltage, the first combined drive and termination circuit comprising:
- a variable impedance pull-up network;
- a variable impedance pull-down network;
- at least one control input for setting a configuration of the pull-up network;
- and
- at least one control input for setting a configuration of the pull-down network;
- and
- a replica of at least part of the combined drive and termination circuit for use in performing calibration;
- the pull-up network comprising a plurality of N-type mosfet transistors, and the pull-down network comprising a plurality of N-type mosfet transistors, the apparatus further comprising a controller that controls calibration being performed in two steps:
- 1) N device output impedance calibration to determine how many of the N-type transistors to enable for drive mode when a data output is logic low;
- 2) N device termination calibration to determine how many of the N-type transistors to enable for termination;
- the apparatus having a termination mode of operation in which the variable impedance pull-up network is configured to have a pull-up network termination impedance and the variable impedance pull-down network is configured to have a pull-down network termination impedance, the pull-up network and the pull-down network in combination functioning as a split termination;
- the apparatus having a drive mode of operation in which:
- to drive a high output, the pull-up network is configured to generate a specific impedance when switched ON;
- to drive a low output, the pull-down network is configured to generate a specific impedance when switched ON;
- each of the pull-up network and the pull-down network having a plurality of transistors sized to provide identical impedances, and
- each of the pull-up network and the pull-down network being configured to have a desired impedance by progressively varying the number of switched ON transistors.
14 more elements
An arrangement comprising:
- a plurality of apparatuses each comprising:
- a first combined drive and termination circuit configured to operate with a first supply voltage, the first combined drive and termination circuit comprising:
- a variable impedance pull-up network;
- a variable impedance pull-down network;
- at least one control input for setting a configuration of the pull-up network;
- and
- at least one control input for setting a configuration of the pull-down network;
- and
- interconnections that pass common calibration values using one or more thermometer codes to each combined drive and termination circuit
- each apparatus having a termination mode of operation in which the variable impedance pull-up network is configured to have a pull-up impedance and the variable impedance pull-down network is configured to have a pull-down network termination impedance, the pull-up network and the pull-down network in combination functioning as a split termination;
- each apparatus having a drive mode of operation in which:
- to drive a high output, the pull-up network is configured to generate a specific impedance when switched ON;
- to drive a low output, the pull-down network is configured to generate a specific impedance when switched ON;
- each of the pull-up network and the pull-down network having a plurality of transistors sized to provide identical impedances, and
- each of the pull-up network and the pull-down network being configured to have a desired impedance by progressively varying the number of switched ON transistors.
12 more elements
A method of providing combined drive and termination, the method comprising:
- in a termination mode of operation, configuring a variable impedance pull-up network forming part of a combined drive and termination circuit to have a pull-up network termination impedance and configuring a variable impedance pull-down network forming part of the combined drive and termination circuit to have a pull-down network termination impedance, the pull-up network and the pull-down network in combination functioning as a split termination;
- in a drive mode of operation, to drive a high output, using first pre-drivers to configure the pull-up network to generate a first drive impedance;
- in the drive mode of operation, to drive a low output, using second pre-drivers to configure the pull-down network to generate a second drive impedance;
- wherein each of the pull-up network and the pull-down network has a plurality of transistors sized to provide identical impedances, and
- configuring each of the pull-up network and the pull-down network to have a desired impedance by progressively varying the number of switched ON transistors;
- and
- performing calibration to calibrate the pull-up termination impedance, the pull-down termination impedance, the first drive impedance and the second drive impedance;
- wherein performing calibration comprises:
- calibrating the pull-up network for drive mode when a data output is logic high;
- calibrating the pull-down network for drive mode when a data output is logic low;
- calibrating the pull-up network for termination mode;
- and
- calibrating the pull-down network calibration for termination mode.
10 more elements
Dependencies are inferred from the claim text.