Miscellaneous active electrical nonlinear devices – circuits – and – Signal converting – shaping – or generating – Current driver
Reexamination Certificate
2000-04-04
2002-03-05
Cunningham, Terry D. (Department: 2816)
Miscellaneous active electrical nonlinear devices, circuits, and
Signal converting, shaping, or generating
Current driver
C327S108000, C327S390000, C326S080000, C326S087000
Reexamination Certificate
active
06353345
ABSTRACT:
BACKGROUND OF THE INVENTION
FIELD OF THE INVENTION
The invention relates to half bridge driver integrated circuits. More particularly, this invention relates to the preparation of a high voltage half bridge integrated circuit with level shifting input control where all complementary metal oxide semiconductor (CMOS) components have been replaced with N- and P-channel double diffused metal oxide semiconductor (DMOS) components.
A high voltage, half bridge integrated circuit (IC) with level shifting input control serves a very important function that is used ubiquitously in many areas of power and control electronics. Presently this function is integrated using full mask silicon on insulator (SOI) technology that requires numerous masking steps to implement.
A half bridge driver integrated circuit (IC), such as the one shown in FIG.
1
and identified by the numeral
1
, typically comprises two, i.e., high and low, power metal oxide silicon (MOS) field effect transistor (FET) or insulated gate bipolar transistor (IGBT) switches
11
,
12
. The half bridge driver IC
1
further comprises a circuit
2
used for generating two square wave signals to control the timing of conduction time to power switches
11
,
12
. This circuit
2
is called a “non-overlap” circuit since signals from circuit
2
conducted to power switches
11
,
12
are controlled so that the switches
11
,
12
do not “overlap,” that is they are not switching on at the same time. The dead time between the two signals avoids any cross conduction of the two power switches
11
,
12
and prevents the simultaneous switching on of both these power switches
11
,
12
.
The half bridge driver IC
1
further comprises two high voltage level shifter MOSFET transistors
5
a
,
5
b
, each of these level shifter transistors being connected with a distinct current source
4
a
,
4
b
. Each of the distinct current sources receives separate Ion and Ioff voltage pulses from a circuit
3
, called the pulse generator circuit, which is used to generate short voltage pulses. The pulse generator circuit
3
generates two short pulses to control the on time switch of the current sources
4
a
,
4
b
. Short pulses instead of long ones are used in order to reduce the level shifting power dissipation. Pulses from the pulse generator circuit
3
are sent to the two current sources
4
a
,
4
b
, which are switched on or off according to the input pulse.
Current passage is allowed from each current source
4
a
,
4
b
through respective transistors
5
a
,
5
b
, which may have ranges of up to a few hundred Volts and are used to communicate between the ground reference level and high voltage reference level, e.g., 500 Volt. These transistors
5
a
,
5
b
may sustain a high voltage across their drain and source. Other devices such as regular CMOS or DMOS are not able to handle such high voltage.
A pulse filter circuit
6
receives short current pulses initiated by the current sources and passed by the level shifter transistors. In its turn the pulse filter circuit
6
generates two voltage levels to activate a latch or flip flop
7
which, according to its received input signals, sends an on or off output signal to switch the high power switch
11
on and off even in the presence of a large common mode current arising from dv/dt coupling. A high side driver
8
is positioned between the latch
7
and the power switch
11
to drive the top power switch
11
.
Moreover, a voltage step up circuit
13
is positioned to receive and to translate the square wave signal from the non-overlap circuit
2
to the low side driver circuit
9
, which will drive the low power switch
12
. The high side and low side drivers
8
,
9
provide sufficient driving power capabilities for the half bridge power switches
11
,
12
, which may be integrated in the half bridge driver IC
1
, to turn on or off the half bridge power switches
11
,
12
, which provide the high voltage square wave to its load as may be specified.
The half bridge driver IC
1
further comprises a bootstrap diode
16
that is connected on one side to a bootstrap capacitor
10
, which in turn is connected to the pulse filter
6
, the latch
7
, the high driver
8
, and in between the high transistor
11
and the low transistor
12
. On the second side, the bootstrap diode
16
is connected to the low supply generator
14
for supplying voltage to the non-overlap circuit
2
, the pulse generator circuit
3
, and the step-up circuit
13
.
It is important to note that in the present state of the art, low voltage circuits such as the non-overlap circuit
2
, the pulse generator circuit
3
, and the current sources
4
use a low threshold complementary MOS (CMOS) with a typical 1 Volt threshold. Other circuits and components, such as the pulse filter
6
, the latch
7
, the high side driver
8
, and the low side driver
9
use a double diffused MOS (DMOS) rather than CMOS. DMOS components allow for higher supply of voltage, i.e., 12 Volt, to sufficiently drive the half bridge power switches
11
,
12
.
Different types of IC components, such as DMOS and CMOS, require more masking steps in the IC manufacturing process making the manufacturing of such a circuit much more expensive than the manufacture of a circuit having components of only one type since the manufacturer's cost is somewhat proportional to the number of masking steps. Furthermore, the non-overlap circuit
2
and the pulse generator circuit
3
are implemented with the low supply generator
14
supplying voltage, e.g., 5 Volt, whereas circuits such as the pulse filter
6
, the latch
7
, the low side driver
9
and the high side driver
8
are implemented with higher supply voltages, e.g., 12 Volt. A supply generator
14
is required to provide low supply, i.e., 5 Volt, from a higher supply, e.g., 12 Volt. Furthermore, The voltage step up circuit
13
is required to translate signals from the non-overlap circuit
2
to the low side driver circuit
9
. Those voltage supply differences make the design and the manufacture of such a circuit complicated, require larger area consumption by the IC, and make the circuit expensive to manufacture.
Finally, an additional problem exists in the pulse filter
6
, which is shown in detail in FIG.
2
. High threshold voltage P-channel DMOS transistors
20
a
,
20
b
are used in the manufacture of the pulse filter
6
. Typically, the DM
0
S FET has a threshold voltage of 3.5 Volt for an N-channel and −5 Volt for a P-channel. In order to turn one of the two P-channel DMOS transistors
20
a
,
20
b
on, at least the threshold voltage drop of the transistor
20
is required to be applied across one of the two resistors
21
a
,
21
b
connected to the gate of the DMOS transistor. When the voltage drop across resistors
21
a
,
21
b
is insufficient to turn on the DMOS transistor, the DMOS will not conduct. Therefore a voltage cannot be created across resistor
22
to turn on one of the inputs to the latch
7
. Consequently the latch
7
will not provide the correct output and therefore will not work in the right state. Furthermore, low resistance is desired of both resistors
21
a
,
21
b
of the pulse filter
6
to maintain low voltage drop across them in the presence of a large common mode level shifting current arising from dv/dt coupling. On the other hand, high resistance is desired in order to utilize the low differential level shifting current to save power dissipation.
It would be advantageous to have a circuit having sufficient margin of output voltage swing and low differential current input. That circuit is less expensive to manufacture than those presently available and takes minimum footprint area.
SUMMARY OF THE INVENTION
The present invention introduces a low cost half bridge driver IC that overcomes the drawbacks of the prior art. In particular this invention introduces a half bridge driver IC, which is fabricated in the process technology with a minimum or reduced number of masking steps to implement all the blocks and without the use of the low threshold voltage CMOS. The invent
Wong Stephen L.
Yushan Li
Cunningham Terry D.
Nguyen Long
Philips Electronics North America Corporation
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