POWER ON DETECTION CIRCUIT

• US 20080218223A1
• Filed: 02/26/2008
• Published: 09/11/2008
• Est. Priority Date: 03/05/2007
• Status: Active Grant

• Current Assignee: North Star Innovations Inc. (Wi-LAN Inc.)
• Original Assignee: Freescale Semiconductor, Inc. (NXP Semiconductors NV)
• Inventors: Kimura, Hiroyuki
• Granted Patent: US 7,612,588 B2
• Time in Patent Office: Days
• US Class Current: 327/142
• CPC Class Codes: H03K 17/223 in field-effect transistor switches
• CPC Class Codes: H03K 5/19 Monitoring patterns of pulse trains indicating amplitude G01R19/00; indicating frequency G01R23/00; measuring characteristics of individual pulses G01R29/02

Abstract

A power on detection circuit for accurately detecting an input voltage with a simple circuit structure and reduced current consumption includes a voltage conversion circuit, which converts input voltage into current, and a latch circuit, which holds the power on detection signal. The voltage conversion circuit supplies output current to a current source and a capacitor via a connection node. The current source generates a flow of current that is proportional to the absolute temperature. When the output current of the voltage conversion circuit becomes greater than the current of the current source, the capacitor is charged and the voltage at the connection node is pulled up. A latching circuit is activated in accordance with the voltage at the connection node to output a power on detection signal.

Claims

1. A power on detection circuit comprising:

a converting means for converting input voltage into converted current that is proportional to an absolute temperature and outputting the converted current;

a first connection node supplied with the converted current from the converting means;

a first current source supplied with the converted current from the first connection node, wherein the first current source generates a flow of first current that is proportional to the absolute temperature and outputs the first current at a value that is the same as the value of the converted current when the input voltage becomes equal to a target voltage;

a first filter connected to the first connection node; and

a latching means for outputting and holding a power on detection signal corresponding to a potential at the first connection node that is generated by the first filter when the value of the first current exceeds the value of the converted current.

2. The power on detection circuit according to claim 1, wherein when the value of the first current exceeds the value of the converted current, the latching means outputs a feedback signal and pulls up the potential at the first connection node in accordance with the feedback signal.

3. The power on detection circuit according to claim 1, wherein:

the latching means outputs and provides the converting means with a feedback signal when the value of the first current exceeds the value of the converted current; and

the converting means stops the output of the converted current in accordance with the feedback signal.

4. The power on detection circuit according to claim 1, wherein the latching means outputs a feedback signal when the value of the first current exceeds the value of the converted current, the power on detection circuit further comprising:

a switch means provided with the feedback signal and arranged between the first connection node and the first current source, wherein the switch means stops the supply of the converted current to the first current source in accordance with the feedback signal.

5. The power on detection circuit according to claim 1, wherein the latching means includes a resetting means for setting the potential at the first connection node to a common potential in accordance with a reset signal and stopping the output of the power on detection signal.

6. The power on detection circuit according to claim 1, further comprising:

a current comparator connected to the first connection node and including a second current source suppliable with current having a second current value, a third current source for generating a flow of current having a third current value that is smaller than the second current value, and a switch element; and

a second filter for receiving output current of the current comparator via a second connection node, wherein;

the potential at the first connection node drives the switch element of the current comparator and supplies the third current source with synthesized current supplied from the first connection node and the second current source; and

the latching means holds the power on detection signal generated by the second filter and output in correspondence with a potential at the second connection node when the synthesized current exceeds the third current value.

7. The power on detection circuit according to claim 6, wherein the latching means includes a resetting means for setting the potential at the second connection node to a common potential in accordance with a reset signal and stopping the output of the power on detection signal.

8. A power on detection circuit, comprising:

a voltage converter circuit for converting an input voltage into a converted current that is proportional to an absolute temperature;

a first node connected to the converter circuit and receiving the converted current;

a first current source connected to the first node and receiving the converted current, wherein the first current source generates a first current that is proportional to the absolute temperature, and wherein the first current is equal to the converted current when the input voltage equals a target voltage;

a first filter connected to the first node; and

a latch circuit connected to the first filter for outputting a power on detection signal corresponding to a potential at the first node that is generated by the first filter when the value of the first current exceeds the value of the converted current.

9. The power on detection circuit of claim 8, wherein the latch circuit includes a reset circuit for setting the potential at the first connection node to a common potential in accordance with a reset signal and inhibiting the output of the power on detection signal.