Semiconductor circuit and constant voltage regulator employing same

• US 8,525,580 B2
• Filed: 06/30/2011
• Issued: 09/03/2013
• Est. Priority Date: 07/15/2010
• Status: Active Grant

• Current Assignee: Nisshinbo Micro Devices Incorporated
• Original Assignee: Ricoh Company Limited
• Inventors: Morino, Koichi, Ito, Masatoshi, Kashima, Yuki, Sakai, Shimpei
• Primary Examiner(s): Hiltunen, Thomas J
• Application Number:
  US13/173,024
• Publication Number:
  US 20120013396A1
• Time in Patent Office: 796 Days
• Field of Search: None
• US Class Current: 327/540
• CPC Class Codes: G05F 3/24 wherein the transistors are of the field-effect type only G05F3/205, G05F3/26, G05F3/30 take precedence

Abstract

A semiconductor circuit includes a voltage regulator and a buffer transistor. The voltage regulator converts an input voltage input to an input terminal thereof into an output voltage output to an output terminal thereof. The buffer transistor is an n-channel depletion-mode metal-oxide semiconductor field effect transistor, disposed between the power supply terminal and the voltage regulator with a gate terminal thereof connected to the power supply terminal, a drain terminal thereof connected to the power supply terminal, and a source terminal thereof connected to the input terminal of the voltage regulator.

Claims

1. A semiconductor circuit for use in connection with a power supply terminal, the circuit comprising:

a voltage regulator to convert an input voltage input to an input terminal thereof into an output voltage output to an output terminal thereof; and

a buffer transistor, being an n-channel depletion-mode metal-oxide semiconductor field effect transistor, disposed between the power supply terminal and the voltage regulator with a gate terminal thereof connected to the power supply terminal, a drain terminal thereof connected to the power supply terminal, and a source terminal thereof connected to the input terminal of the voltage regulator, a voltage at the gate terminal being higher than a voltage at the source terminal.

2. The semiconductor circuit according to claim 1, further comprising a resistor disposed between the power supply terminal and the drain terminal of the buffer transistor.

3. The semiconductor circuit according to claim 1, further comprising:

a resistor disposed between the power supply terminal and the gate terminal of the buffer transistor; and

a capacitor disposed between a ground and the gate terminal of the buffer transistor.

4. The semiconductor circuit according to claim 1, wherein the voltage regulator is implemented in an integrated circuit containing one or more circuit components integrated into a single integrated unit, at least one of the circuit components supplied with the output voltage regulated through the voltage regulator.

5. The semiconductor circuit according to claim 1, wherein the voltage regulator includes a driver transistor connected between the input and output terminals thereof, the source terminal of the buffer transistor being connected solely to a conductive terminal of the driver transistor.

6. The semiconductor circuit according to claim 5, further comprising a resistor disposed between the power supply terminal and the drain terminal of the buffer transistor.

7. The semiconductor circuit according to claim 5, further comprising:

a resistor disposed between the power supply terminal and the gate terminal of the buffer transistor; and

a capacitor disposed between a ground and the gate terminal of the buffer transistor.

8. The semiconductor circuit according to claim 5, wherein the voltage regulator is implemented in an integrated circuit containing one or more circuit components integrated into a single integrated unit, at least one of the circuit components being supplied with the output voltage regulated through the voltage regulator.

9. The semiconductor circuit according to claim 8, wherein the driver transistor of the voltage regulator is an n-channel field effect transistor.

12. The semiconductor circuit according to claim 1, wherein the voltage at the gate terminal of the buffer transistor is equal to a voltage at the drain terminal of the buffer transistor.

13. The semiconductor circuit according to claim 1, wherein the voltage regulator includes a differential amplifier having a positive power supply input terminal connected to the drain terminal of the buffer transistor.

14. The semiconductor circuit according to claim 1, wherein the voltage regulator includes a reference voltage generator having an input terminal thereof connected to the drain terminal of the buffer transistor.

15. The semiconductor circuit according to claim 1, wherein the voltage regulator comprises:

a reference voltage generator outputting a reference voltage and having an input terminal thereof connected to the drain terminal of the buffer transistor; and

a differential amplifier having a positive power supply input terminal connected to the drain terminal of the buffer transistor, wherein the reference voltage output by the reference voltage generator s supplied to an inverting terminal of the differential amplifier.

10. A voltage regulator for use in connection with a power supply terminal, the voltage regulator comprising:

an input terminal to receive an input voltage supplied from the power supply terminal;

an output terminal to output an output voltage to load circuitry;

a driver transistor connected between the input and output terminals to convert the input voltage into the output voltage; and

a buffer transistor, being an n-channel depletion-mode metal-oxide semiconductor field effect transistor, disposed between the power supply terminal and the voltage regulator with a gate terminal thereof connected to the power supply terminal, a drain terminal thereof connected to the power supply terminal, and a source terminal thereof connected to the input terminal of the voltage regulator, a voltage at the gate terminal being higher than a voltage at the source terminal.

11. The voltage regulator according to claim 10, wherein the source terminal of the buffer transistor is connected solely to a conductive terminal of the driver transistor.