Reference voltage generating circuit and power supply device using the same

• US 7,982,531 B2
• Filed: 03/20/2007
• Issued: 07/19/2011
• Est. Priority Date: 03/31/2006
• Status: Expired due to Fees

• Current Assignee: RICOH Electronic Devices Co., Ltd. (Nisshinbo Holdings Incorporated)
• Original Assignee: Ricoh Company Limited
• Inventors: Nakanishi, Hiroaki, Yoshida, Masaaki
• Primary Examiner(s): Donovan; Lincoln
• Assistant Examiner(s): ENGLUND, TERRY LEE
• Application Number:
  US11/915,440
• Publication Number:
  US 20090146731A1
• Time in Patent Office: 1,582 Days
• Field of Search: None
• US Class Current: 327/543
• CPC Class Codes: H01L 27/0883 Combination of depletion and enhancement field effect transistors

Abstract

A reference voltage generating circuit for generating a reference voltage includes MOSFETs connected to each other. At least one of the MOSFETs includes a control gate and a floating gate that is made hole-rich or discharged by ultraviolet irradiation, and the reference voltage generating circuit is configured to output the difference between threshold voltages of a pair of the MOSFETs as the reference voltage.

Claims

1. A reference voltage generating circuit for generating a reference voltage, comprising:

at least a pair of MOSFETs connected to each other;

wherein

only one of the pair of MOSFETs includes a control gate and a floating gate;

holes are injected into the floating gate of the one of the pair of MOSFETs; and

the reference voltage generating circuit is configured to output a difference between threshold voltages of the pair of MOSFETs as the reference voltage,

wherein the pair of MOSFETs are P-channel MOSFETs each having a depletion-mode threshold voltage as an initial threshold voltage.

2. A power supply device, comprising:

the reference voltage generating circuit as claimed in claim 1; and

a detection circuit configured to detect a change in a power supply voltage by comparing the power supply voltage with the reference voltage supplied from the reference voltage generating circuit.

3. A power supply device, comprising:

a reference voltage generating circuit for generating a reference voltage, said reference voltage generating circuit comprising;

at least a pair of MOSFETs connected to each other, wherein

only one of the pair of MOSFETs includes a control gate and a floating gate,

holes are injected into the floating gate of the one of the pair of MOSFETs, and

the reference voltage generating circuit is configured to output a difference between threshold voltages of the pair of MOSFETs as the reference voltage; and

a detection circuit configured to detect a change in a power supply voltage by comparing the power supply voltage with the reference voltage supplied from the reference voltage generating circuit.