Sean A Chen

US Patent:

6404266, Jun 11, 2002

Filed:

Jul 25, 2000

Appl. No.:

09/624738

Inventors:

Sean S. Chen - Sunnyvale CA

Assignee:

National Semiconductor Corporation - Santa Clara CA

International Classification:

H03K 1760

US Classification:

327478, 327 53, 327563

Abstract:

A differential input stage with full-rail sensing and reduced latch-up susceptibility includes an emitter-coupled pair, a current mirror, and several series resistors. For a NPN emitter-coupled pair, a series resistor is connected between the input node and the base of each transistor of the emitter-coupled pair, and a series resistor is connected between each load resistor and its corresponding current mirror transistor. The series resistors reduce current flowing into the PN junctions when power to the overall circuit is disabled but an input signal is present at the input terminals.

US Patent:

6433516, Aug 13, 2002

Filed:

Jun 11, 2001

Appl. No.:

09/879474

Inventors:

Sean S. Chen - Sunnyvale CA

Assignee:

National Semiconductor Corporation - Santa Clara CA

International Classification:

H02J 716

US Classification:

320150

Abstract:

A temperature stabilized, constant current source capable of charging a fully discharged battery of the present invention includes a feedback control stage that provides a substantially constant battery charging current at a particular temperature. A temperature stabilized current source stage coupled to a bias resistor includes a negative temperature coefficient current source that provides a countervailing control current to a positive temperature coefficient current source that is coupled from a sensing resistor. The temperature dependencies of the positive and negative temperature coefficient current sources tend to cancel each other out so as to provide a temperature stabilized current to the sensing resistor. The bias resistor provides a bias current to the temperature stabilized current source stage in such a way that the temperature stabilized current source stage provides a charging current to a fully discharged battery.

US Patent:

6621333, Sep 16, 2003

Filed:

Dec 11, 2001

Appl. No.:

10/014728

Inventors:

Sean S. Chen - Sunnyvale CA

Assignee:

National Semiconductor Corporation - Santa Clara CA

International Classification:

H03F 102

US Classification:

330 9, 330256, 330265, 327307

Abstract:

A circuit for countering offset voltage in an amplifier induced by changes in the output load. The circuit comprises an input stage, an output stage, and first and second current compensation stages. The first current compensation stage is coupled to the output stage and produces a first compensation current that is a function of the output current. The input stage is coupled to the first current compensation stage from which it receives the first compensation current. The input stage is configured to cause a change in the voltage between its input terminals in response to the first compensation current. The second current compensation stage produces a second compensation current, which is also fed into the input stage to act jointly with the first compensation current. The first compensation current may be linearly related to the output current. The second compensation current may be exponentially related to the output current.

US Patent:

6788143, Sep 7, 2004

Filed:

Apr 29, 2002

Appl. No.:

10/136196

Inventors:

Sean S. Chen - Sunnyvale CA

Assignee:

National Semiconductor Corporation - Santa Clara CA

International Classification:

H03F 345

US Classification:

330253, 330311

Abstract:

A cascode stage is arranged to improve performance of an operational amplifier. The cascode stage includes transistors that are arranged to operate as a current mirror. Each side of the current mirror has a corresponding voltage at a corresponding node. One of the corresponding nodes corresponds to a high impedance node that is coupled to a subsequent stage of the amplifier. The voltages at the corresponding nodes are closely matched to one another such that the input referred offset in the amplifier is minimized and the power supply rejection ratio is improved (PSRR). A transistor threshold voltage and a transistor saturation voltage determine the headroom requirements of the cascode stage, such that low power supply voltage operation is possible. The biasing of the transistors in the cascode stage is simplified such that minimal biasing circuitry is required, and overall power consumption may be minimized.

US Patent:

6819164, Nov 16, 2004

Filed:

Oct 17, 2002

Appl. No.:

10/274313

Inventors:

Sean S. Chen - Sunnyvale CA

Assignee:

National Semiconductor Corporation - Santa Clara CA

International Classification:

G05F 110

US Classification:

327540, 327543, 327404, 323312, 323313, 323315

Abstract:

A circuit is arranged to enable bi-directional trimming of a reference voltage. A trim current is generated by mirroring a bias current using one or more selectable current source circuits. The selectable current source circuits may each contain transistors that are sized differently from corresponding transistors of the other selectable current source circuits. The sizing may be arranged in a binary chain such that a range of currents may be generated for the trim current while allowing for selection of the level of adjustment for the reference voltage. The current selected for the trim current depends on which of the selectable current sources is enabled. The node corresponding to the trim current is selectively coupled to a load to either increase the voltage across the load or decrease the voltage across the load, providing bi-directional trimming of the reference voltage measured across the load.

US Patent:

6914494, Jul 5, 2005

Filed:

Aug 26, 2003

Appl. No.:

10/649085

Inventors:

Sean S. Chen - Sunnyvale CA, US

Assignee:

National Semiconductor Corporation - Santa Clara CA

International Classification:

H03L007/00

US Classification:

331111, 143185, 143173

Abstract:

A low current oscillator circuit comprising a comparator for driving an output signal. A first capacitor chain is coupled to the comparator. The first capacitor chain is configured for setting a first input voltage of the comparator. A second capacitor chain is also coupled to the comparator. The second capacitor chain is configured for setting a second input voltage of the comparator, wherein the first capacitor chain and the second capacitor chain determine a first voltage level and a second voltage level of oscillation of the comparator. The first capacitor chain and the second capacitor chain are free of DC current flow.

US Patent:

7400187, Jul 15, 2008

Filed:

Oct 2, 2001

Appl. No.:

09/970297

Inventors:

Sean S. Chen - Sunnyvale CA, US

Assignee:

National Semiconductor Corporation - Santa Clara CA

International Classification:

G05F 1/10

US Classification:

327539, 323313

Abstract:

The present invention relates to a low impedance band-gap voltage reference circuit which comprises a band-gap reference circuit, a buffer circuit to reduce the impedance and related noise associated with band-gap references electronically coupled with the band-gap voltage reference circuit and a voltage pull-up device electronically coupled with both the band-gap reference circuit and the buffer circuit. The voltage pull-up device acts to reduce the supply voltage required to maintain a stable, low Z band-gap reference voltage.

US Patent:

7551624, Jun 23, 2009

Filed:

Jun 9, 2005

Appl. No.:

11/148948

Inventors:

Sean Chen - Sunnyvale CA, US
Yongdong Zhao - Pleasanton CA, US
Zesen Chen - Pleasanton CA, US

Assignee:

SBC Knowledge Ventures, L.P. - Reno NV

International Classification:

H04L 12/28

US Classification:

37039521, 370352

Abstract:

A communications system is described for enforcing a service level agreement for a specified customer on a network. The communications system includes a router to receive at least one packet containing data. A management system is in communication with the router, where the management system provides access control commands to the router for the specified customer based upon an agreed upon codec and an agreed upon packet length. A detection system is in communication with the router. The detection system extracts a codec information and a packet length information from the packet. If the codec matches the agreed upon codec and the packet length matches the agreed upon packet length, then the packet is allowed to proceed. Otherwise the packet is dropped from the network.