Comparing and amplifying detector circuit

Details Comparing and amplifying detector circuit Comparing and amplifying detector circuit

1999-09-16

2001-11-13

Cunningham, Terry D. (Department: 2816)

Miscellaneous active electrical nonlinear devices, circuits, and

Specific signal discriminating without subsequent control

By amplitude

C327S053000, C327S066000, C327S070000, C327S512000, C330S257000

Reexamination Certificate

active

06316971

ABSTRACT:

FIELD OF THE INVENTION
This invention relates to a comparing detector circuit and, more particularly, to a comparing and amplifying detector circuit for performing voltage comparison and amplification and detection of temperature. The invention further relates to a comparing and amplifying detector circuit ideal for use in a power MOSFET having an internal protection function.
BACKGROUND OF THE INVENTION
A comparator of the kind disclosed in, e.g., the specification of Japanese Patent Kokai (Laid-Open) Publication JP-A-5-14073 has been proposed as a comparing and amplifying detector circuit in the prior art. The comparator, which uses a differential amplifier, employs depletion-type MOS transistors as amplifying elements and is adapted in such a manner that a digital signal is obtained even for an input voltage in the low-level range.
FIG. 10
is a diagram showing a circuitry of the comparator disclosed in this publication. A constant current, which is obtained by a depression-type transistor
201
whose drain is connected to a power supply and whose gate and source are tied together, is input as a reference current to the input side of enhancement-type transistors
202
,
207
that construct a current mirror circuit. An output current of the current mirror circuit is supplied as a driving current to transistors
204
,
206
forming a differential pair and having sources that are tied together, gates to which input terminals
10
,
11
are respectively connected and drains that are respectively connected to load elements (depletion-type transistors whose drains are connected to the power supply and each of whose gate and source are tied together)
203
,
205
. A drain of the transistor
206
is connected to the input of an inverter comprising a depletion-type transistor
208
and an enhancement-type transistor
209
, namely to a gate of the transistor
209
. A signal applied to this inverter is inverted and amplified thereby and output at an output terminal
12
.
A circuit of the kind shown in
FIG. 12
is known as a comparator used in electrical equipment in automobiles. The comparator has a power supply
1
, a control IC
13
arranged on control ground
16
; a battery
222
, a low-side PID (intelligent power device)
220
and a load
221
arranged on power ground
18
: interface resistors
211
,
212
,
214
,
215
,
217
and
218
; transistors
213
,
216
; and a voltage regulator diode
219
.
In the operation of the circuit shown in
FIG. 12
, the output voltage of the control IC
13
is potentially divided by the resistors
211
,
212
and the resulting voltage is applied to the base of the NPN transistor
213
. By turning the transistor
213
on and off, the PNP transistor
216
is turned on and off, the voltage of the battery
222
is clamped by the voltage regulator diode
219
and a signal is applied to an input of the low-side IPD
220
.
The specification of Japanese Patent Kokai (Laid-Open) Publication JP-A-6-244414 discloses an arrangement serving as a temperature detector circuit in which, as shown in FIG.
13
(A), a constant current obtained by a depletion-type transistor
223
flows into a diode group of serially connected diodes
224
, and a potential at a connection node between the depletion-type transistor
223
and the diode group
224
is input to a gate of an enhancement-type transistor
226
and is compared with a threshold voltage VT of the transistor
226
, whereby temperature is detected utilizing the temperature dependence illustrated in FIG.
13
B.
SUMMARY OF THE DISCLOSURE
In the course of eager investigations toward the present invention, the following problems have been encountered.
The circuits according to the prior art set forth above have certain problems, described below.
The comparator depicted in
FIG. 10
requires that threshold voltage VT of the transistor
209
be changed in conformity with the input voltages used. In the case of a semiconductor integrated circuit, therefore, an additional process for changing the threshold voltage VT of transistor
209
is necessary and the device has very little versatility.
The reason for this is as follows:
Since the depletion-type transistors
203
,
205
are both constant-current sources, the following inequality:
(current of transistors
203
,
205
)<(current of transistor
207
)<(sum of currents of transistors
203
and
205
)
is a condition for allowing a gate voltage of the transistor
209
to be changed with respect to inputs
10
,
11
. Consequently, as shown in
FIG. 11
, the depletion-type transistor
206
limits the current of the transistor
205
within the range:
(voltage of input
10
)≦(voltage of input
11
), and therefore the drain voltage of the transistor
207
becomes:
(voltage of input
10
)−(threshold voltage VT of transistor
206
), and the gate voltage of the transistor
209
becomes approximately the voltage of power supply
1
.
Further, the depletion-type transistor
204
limits the current of the transistor
203
within the range:
(voltage of input
10
)≧(voltage of input
11
), and therefore the drain voltage of the transistor
204
becomes:
(voltage of input
11
)−(threshold voltage VT of transistor
204
), and the gate voltage of the transistor
209
becomes a voltage that is approximately the drain voltage of transistor
207
.
Thus, the gate voltage of the transistor
209
ranges from the voltage of the power supply
1
to [(voltage of input
11
)−(threshold voltage VT of transistor
204
)].
In the circuit shown in
FIG. 12
, a resistance-containing transistor constituted by the resistors
211
,
212
and transistor
213
and a resistance-containing transistor constituted by the resistors
214
,
215
and transistor
216
are required between the control IC
13
and low-side IPD
220
. This makes it difficult to miniaturize the device.
The reason for this is as follows:
The output voltage of the ordinary control IC
13
is
VOH≧VDD×
0.7
VOL≦
0.3×
VDD
where VOH represents the high level of the output voltage and VOL the low level of the output voltage. Further, VDD is the voltage of the power supply
1
, e.g., 5±0.5 V. When a fluctuating voltage
17
(e.g., ±1.5 V) between grounds is taken into account, the high and low levels of the control IC
13
cannot be discriminated from the low-side IPD
220
.
A problem which arises with the circuit shown in FIG.
13
(A) is a wide range of variation in detected temperature. The reason for this is as follows:
Let the temperature dependence of the forward voltage drop (VF) of diode group
224
be, e.g., 2 mV/° C.×5 stages=10 mV/° C., and let variation of the threshold voltage VT of transistor
226
be ±300 mV. Under these conditions, the range of variation in detected temperature will be ±300 mV÷10 mV/° C.=±30° C.
The present invention has been devised in view of the foregoing problems, and an object is to provide a comparator circuit that is capable of operating irrespective of the input voltages.
Another object of the present invention is to provide a comparing detector circuit that does not require resistor-containing transistors, thus making it possible to miniature devices having the circuit.
A further object of the present invention is to provide a detector circuit in which detection variance is reduced and precision improved.
According to a first aspect of the present invention, the foregoing objects are attained by providing a voltage comparator circuit comprising: a first pair of transistors to which first and second input signal voltages are input for functioning as a buffer; a second pair of transistors constructing a current mirror circuit in which an input node and an output node are connected to the first pair of transistors via first and second resistors, respectively; and an output transistor to which potential at the output node of the current mirror circuit is applied as an input.
According to a first variant to the first aspect, there is provided a voltage comparator circuit comprising: first a

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