Power-up circuit for analog circuit

Details Power-up circuit for analog circuit Power-up circuit for analog circuit

2000-05-19

2001-07-10

Berhane, Adolf Deneke (Department: 2838)

Electricity: power supply or regulation systems

Self-regulating

Using a three or more terminal semiconductive device as the...

C323S315000, C323S901000

Reexamination Certificate

active

06259240

ABSTRACT:

FIELD OF THE INVENTION
The invention relates to a start-up circuit for enabling a circuit from a power-down mode.
BACKGROUND OF THE INVENTION
To reduce power consumption, circuit portions may be powered down when not in use, and powered up when they are again needed. Start-up circuitry is used to power-up desired circuit portions when needed. This mechanism increases battery life which is particularly desirable for portable electronic devices.
Previous start-up circuits include circuits having an NMOS transistor source tied to a node to be powered up and a drain tied to a power supply, such that the transistor is turned on if the source drops below a threshold which is established below the transistor gate voltage. The transistor is turned off if the source voltage becomes greater than the gate voltage plus the threshold voltage.
Other start-up circuits include those which provide current to a the node to be powered up and then detect when the circuit has powered up and thereafter cease supply of current to the node.
Circuits, for example mixed-signal circuits comprising analog-to-digital and digital-to-analog conversion functions, often require a reference voltage for operation. Voltage reference circuitry establishes the reference voltage when activated by an enabling signal. When high speed operation of a device is desirable it is advantageous to establish the reference voltage within a short duration of receiving the enabling signal. Start-up circuits have been used in conjunction with voltage reference circuits to improve response time.
FIG. 1
depicts a known start-up circuit
100
used in conjunction with a voltage reference circuit
102
. Start-up circuit
100
is shown by dotted lines. Voltage reference circuit
102
has two possible equilibrium points, one of which corresponds to zero voltage and zero current, and a second, non-zero equilibrium point, which corresponds to a useful reference voltage. Therefore, voltage reference circuit
102
must be designed to choose only the non-zero equilibrium point to establish the reference voltage. Start-up circuit
100
is provided to allow voltage reference circuit
102
to utilize only the desired equilibrium point. If voltage reference circuit
102
is at the undesired equilibrium point, the voltage is zero and therefore, I
1
and I
2
are zero. Consequently, transistor
104
provides current in transistor
106
which then moves voltage reference circuit
102
to the non-zero equilibrium point. Transistor
104
's source voltage increases as the desired equilibrium point is approached. This causes the current through transistor
104
to decrease. When voltage reference circuit
102
reaches the non-zero equilibrium point, the current through transistor
106
will be substantially the same as the current through transistor
108
. Transistor
110
and resistor
112
set the gate bias voltage for transistor
104
. Voltage reference circuit
102
is on within a gate bias voltage window. Therefore, the gate bias voltage must be high enough to turn voltage reference circuit
102
on but must not exceed the upper limit of the voltage window.
At startup, no current flows in bandgap circuit
204
. Node
214
is pulled down by the kick-start circuit and node
212
is pulled up by the kick-start circuit. This causes current to flow in transistor
208
and by reflection in transistor
206
which holds node
212
above ground and this reflects current into the other branch to hold node
214
below the power supply and keep bandgap circuit
204
on. When current flows in the transistors of bankgap rteference circuit
204
, kick-start circuit
202
is turned off. This occurs because transistor
205
mirrors the current in transistor
206
which drives the gate node of transistor
209
high and so pulls down node
211
. Driving node
211
low turns off the current mirrors in kick-start circuit
202
, so it stops sourcing and sinking current to the bandgap reference circuit
204
. Resistor
210
ensures that current flows in kick-start circuit
202
when band gap reference circuit
204
is powered down.
SUMMARY OF THE INVENTION
A start-up circuit is disclosed for providing current to an analog circuit wherein the analog circuit contains an operational amplifier. The start-up circuit makes use of normal operation of the analog circuit to perform a power-up function. A node being powered up is at substantially all times controlled by the operational amplifier, minimizing performance variation resulting from process and temperature variations.


REFERENCES:
patent: 4839535 (1989-06-01), Miller
patent: 5452195 (1995-09-01), Lehr et al.
patent: 5666046 (1997-09-01), Mietus
patent: 5668467 (1997-09-01), Pease
patent: 5751142 (1998-05-01), Dosho et al.
patent: 6133719 (2000-10-01), Maulik

Affiliated with

Also associated with

Rating

Power-up circuit for analog circuit does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Power-up circuit for analog circuit, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Power-up circuit for analog circuit will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-2563884