Systems and methods for impedance stabilization

• US 9,325,253 B2
• Filed: 05/13/2013
• Issued: 04/26/2016
• Est. Priority Date: 06/28/2007
• Status: Active Grant

• Current Assignee: Apple Inc.
• Original Assignee: Apple Inc.
• Inventors: Land, Brian, Hotelling, Steve P., Pabon, Gus, Lyon, Benjamin B.
• Primary Examiner(s): Lee, Jr., Kenneth B
• Application Number:
  US13/893,239
• Publication Number:
  US 20130250640A1
• Time in Patent Office: 1,079 Days
• Field of Search: None
• US Class Current: 1/1
• CPC Class Codes: G06F 3/04166 Details of scanning methods, e.g. sampling time, grouping of sub areas or time sharing with display driving Synchronisation with the driving of the display or the backlighting unit to avoid interferences generated internally G06F3/04184
• CPC Class Codes: G06F 3/04182 Filtering of noise external to the device and not generated by digitiser components
• CPC Class Codes: G06F 3/044 by capacitive means
• CPC Class Codes: H02M 7/06 using discharge tubes without control electrode or semiconductor devices without control electrode

Abstract

An AC-to-DC adapter may be provided in order to increase the sensitivity of a touch-sensitive surface. Such an AC-to-DC adapter may include a rectifying circuit to rectify incoming AC signals. The rectifying circuit may take the form of a diode bridge network that includes four diode branches. Stabilization circuits may be provided in parallel with each diode branch in order to decrease the impedance of the diode bridge network during particular periods of operation. The stabilization circuits may be configured such that the impedance of the diode bridge network is substantially constant during all periods of operation. As a result, the impedance of the AC-to-DC adapter may be relatively constant during all periods of operation. In turn, the sensitivity of a touch-sensitive surface of a device being powered by such an AC-to-DC adapter may increase.

Claims

1. An AC-to-DC power adapter comprising:

an input and output;

a diode network for rectifying the input;

an impedance stabilization circuit comprising a resistor and a capacitor coupled in series;

wherein the impedance stabilization circuit is coupled to a diode of the diode network in a parallel configuration;

a transformer having a first winding coupled to the diode network and a second winding coupled to the output; and

a capacitor coupled to the first winding at one end and the second winding at another end.

2. A method comprising:

detecting that an AC-to-DC adapter is not being utilized to power a device, wherein the device includes a touch-sensitive sensor having an output; and

scaling the output upwards to compensate for a reduced sensitivity in the touch-sensitive sensor, wherein the reduced sensitivity occurs as a result of the device not being powered by the AC-to-DC adapter.

3. The method of claim 2, wherein a local system ground of the device is not coupled to the housing of the device.

4. The method of claim 2, further comprising:

detecting that the AC-to-DC adapter is reconnected with the device; and

terminating the scaling.