JPH05304426A - Semiconductor device - Google Patents

Abstract

PURPOSE:To make it possible to constitute a circuit where the range of common mode input voltage is VDD to VSS in normal power supply voltage by using a depression type MOSFET for an input transistor in a loop-back type differential amplifier circuit. CONSTITUTION:A depression type MOSFET is used for input transistors Tr11, Tr12. As a result, the Tr11, Tr12 are not turned off even when the voltage of an input 1 and an input 2 is in the vicinity of VSS. The voltage is not limited even when the voltage of the input 1 and the input 2 is in the vicinity of VDD. Therefore, the common mode input voltage of a differential amplifier circuit is possible to be made VDD to VSS.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor device which constitutes a folded cascade type differential amplifier circuit.

[0002]

2. Description of the Related Art A typical conventional differential amplifier circuit is shown in FIGS. Of the transistors used here, Tr1 and Tr2 in FIG. 4 are depletion type transistors, and the others are all enhancement type transistors.

Further, FIG. 5 shows a typical example of a conventional folded cascade type differential amplifier circuit. Here, all are configured with enhancement type transistors.

[0004]

By the way, in the conventional differential amplifier circuit, the upper limit or the lower limit of the common mode input voltage range is limited to a value below V _DD or above V _SS , respectively.

In the example of FIG. 3, the input transistors Tr1,
Since Tr2 is an enhancement type, if the voltage of input 1 and input 2 is lower than V _{TH of} Tr1 and Tr2, then Tr1,
Tr2 is almost turned off, and the function as an amplifier circuit is lost.

In the example of FIG. 4, the input transistors Tr1 and T1
Since r2 is a depletion type, the input 1, the voltage of the input 2 is operated even near V _SS, when in the vicinity of V _DD, the voltage of the voltage and V _DD of the common source terminal of the Tr1, Tr2 The difference becomes smaller than the absolute value of V _TH of Tr3, and Tr
3, Tr4 is almost turned off, and the function as an amplifier circuit is lost.

In the circuit of FIG. 4, when the back gates of Tr1 and Tr2 are connected to V _SS , when the input voltage is high,
Since V _{TH of} Tr1 and Tr2 moves to the enhancement type, it is possible to set the common mode input range to V _{DD to} V _SS . However, in this case, V _{TH of} Tr1 and Tr2 is Tr3, T
In order to be sufficiently larger than the absolute value of V _TH of r4, a large V
_DD is required and not practical.

In the example of FIG. 5, as in the example of FIG. 3, the function of the input 1 and the input 2 is lost near the voltage V _SS .

The present invention is intended to solve the above problems, and configures a differential amplifier circuit having a common-mode input voltage range of V _{DD to} V _SS at a normal power supply voltage (for example, about 3 V and 5 V). It is an object of the present invention to provide a semiconductor device having

[0010]

To achieve the above object, the present invention provides a folded cascade type differential amplifier circuit in which a depletion type MOSF is used as an input transistor.
It is characterized by using ET.

[0011]

According to the above structure, the input transistor is not turned off even when the input voltage is near V _SS , and the voltage is not limited even near V _DD . Therefore, the common mode input voltage of the differential amplifier circuit can be changed from V _DD to V _SS .

[0012]

Embodiments will be described below in detail with reference to the drawings. 1 shows a folded cascade type differential amplifier circuit according to an embodiment of the present invention, in which the input transistors Tr1 and Tr2 of the conventional circuit shown in FIG.
It is replaced with FETs Tr11 and Tr12. Other configurations are exactly the same.

As described above, in this embodiment, since the input transistors Tr11 and Tr12 are of the depletion type, Tr11 and Tr12 are not turned off even when the voltage of the input 1 and the input 2 is near V _SS . Further, even if the voltage of the input 1 and the input 2 is near V _DD , the voltage is not limited. For example, if Tr14 and Tr15 shown in FIG. 2 are used for the constant current sources 2 and 3, Tr13, Tr14,
If Tr15 is large enough for the constant current value,
Since the drain-source voltages of Tr14 and Tr15 operate sufficiently constant current up to about 0 V, the common-mode input voltage range is from V _{DD to} V _SS.
Can take enough.

In the circuit of FIG. 1, the input transistor T
When the back gates of r11 and Tr12 are connected to V _SS , when the input 1 and the input 2 are near V _DD , the absolute value of the depleted V _TH of Tr11 and Tr12 becomes small or becomes an enhancement, so that the constant current source 2 , 3 is ensured by the circuit of FIG. 1, which is more advantageous.

[0015]

As described above, according to the present invention,
By the depletion type MOSFET used for input,
The common mode input voltage of the differential amplifier circuit can be from V _DD to V _SS .

Further, by connecting the back gate of the depletion type MOSFET to V _SS in the case of the Nch transistor and connecting it to V _DD in the case of the Pch transistor, the operating voltage of the constant current circuit of the load can be secured. The operation of the circuit can be stabilized.

[Brief description of drawings]

FIG. 1 is a circuit configuration diagram of an embodiment of the present invention.

FIG. 2 is a diagram showing a specific circuit of the constant current source of FIG.

FIG. 3 is a configuration diagram of a conventional representative differential amplifier circuit.

FIG. 4 is a configuration diagram of a conventional differential amplifier circuit using a depletion type as an input transistor.

FIG. 5 is a configuration diagram of a conventional typical folded cascade type differential amplifier circuit.

[Explanation of symbols]

Tr5 to Tr8 ... MOSFET, Tr11, Tr12 ... Depletion type MOSFET.

Claims (3)

[Claims] 1. A depletion type MOSF is used as an input transistor in a folded cascade type differential amplifier circuit.
A semiconductor device using ET. 2. The semiconductor device according to claim 1, wherein when the depletion type MOSFET is an Nch transistor, its back gate is connected to V _SS . 3. The semiconductor device according to claim 1, wherein when the depletion type MOSFET is a Pch transistor, its back gate is connected to V _DD .