JPS628605A - Operational amplifier circuit - Google Patents

Abstract

PURPOSE:To improve a power noise rejection ratio even at a high frequency by connecting a frequency compensating circuit between an output terminal connected to a drain of a MISFET of the output stage and a differential pair output. CONSTITUTION:An input signal inputted to a differential input stage and converted from a differential signal into a single signal is amplified by a common gate transistor (TR) M7, amplified inversely by a TR M10 and outputted to an output terminal 3. TRs M6, M8 act like a load and a constant current source of a TR M7 respectively. A frequency compensation circuit comprising a TR MR and a capacitor Cc is connected between the output terminal 3 and an output terminal of the differential stage comprising TRs M1, M2, but not connected between the gate and drain of a TR M9 being a load of the output stage even when the frequency compensation circuit is a low impedance at a high frequency, the TR M9 is not in the form of diode connection and then ease of invasion of power noise through the TR M9 is avoided.

Description

[Detailed description of the invention] (Industrial application field) The present invention relates to an operational amplifier circuit.

(Prior art and its problems) Conventionally, an operational amplifier circuit as shown in FIG. 2 (1988 Institute of Electronics and Communication Engineers General Conference Proceedings 532 Ishigaki et al. 1 Prototype of broadband switched capacitor circuit) is known. 8 in Figure 2, 1 is the input terminal on the + side, 2 is the input terminal on one side, 3 is the output terminal, 4 is the power supply line on the + side, 5 is the power supply line on the one side, 6゜7 is the bias terminal , M1-M5, Ml
1 to M14, MR is a MISFET) transistor, and Cc is a capacitance. In this operational amplifier circuit 2, a signal is amplified and converted from a differential to a single signal by a differential input pair of transistors M1 and M2 (MOSFET) whose source is connected to transistor M5 (MOSFET) which is a constant current source. M
O8F'BT) transistor Mll shifts the signal, MOSFET) transistor M14 inverts and amplifies it, and MO8FET transistor M13 also inverts and amplifies it, and outputs the combined signal to output terminal 3. In addition, a frequency compensation circuit in which a MO8FET transistor MR and a capacitor Cc are connected in series, which functions as a resistor, is connected to the output terminal 3 and the MOSFET transistor MR.
ET) It is connected between the output terminals of the differential pair of transistors M1 and M2 to perform frequency compensation.

In the conventional operational amplifier circuit shown in FIG.
OSFET) A capacitor and a resistor are connected in series between the drain and gate of the transistor M13, and it has a low impedance for high-frequency signals, so it is a MOSFET.
Since the drain and gate of the transistor M13 are connected with low impedance, the MOSFET transistor M13 can be regarded as diode-connected. Therefore, tLI!
@Among voltage noise components, high frequency components are MOSFET)
It passes through the transistor M13 and appears at the output terminal 3, which has the disadvantage that the power supply noise rejection ratio deteriorates at high frequencies.

To eliminate this drawback, MO8FET transistor M13
Considering the operational amplifier circuit shown in Fig. 3 in which the gate of MO8PE'l') is connected to the bias point 8 without connecting the output terminals of the differential pair of transistors M1 and M2, MO8F
] Since the 18T transistor M13 no longer has the function of inverting and amplifying the signal, the gain is reduced compared to the circuit of FIG. 2 by the amount that the MO8PET transistor M13 does not operate as an active element, and the gain of the output stage is equal to that of the MO8PET transistor M13.
Only due to FET transistor M14, 1/2
A shortcoming occurs in that the gain of the output stage is reduced compared to the operational amplifier circuit shown in FIG.

(Objective of the Present Invention) In view of the above points, one object of the present invention is to provide an operational amplifier circuit that has a good power supply noise rejection ratio even at high frequencies and has a high gain.

(Structure of the Invention) The operational amplifier circuit of the present invention includes a MISFET differential pair whose sources are commonly connected to a first constant current source, and the MISFET differential pair whose sources are commonly connected to a first constant current source.
The output of the T differential pair is a first MISFET with a grounded gate whose source (=connected), a second MI8FET connected to the first MI8FET and serving as a second constant current source, and a second MISFET connected to the first MI8FET, which is a second constant current source; A third MISFET with a first load ζ connected to the MISFET, an M4 MI8FET whose gate is connected to the drain of the first MI8FET, and a second load connected to the fourth MISFBT. Fifth
and a frequency compensation circuit connected between the output terminal connected to the drain of the fourth MISFET and the output of the differential pair.

(Example) Next, the present invention will be explained with reference to the drawings.

An embodiment of the present invention is shown in the gi diagram. 9~ in Figure 1
12 is a bias terminal, and M6 to MIO are MOSFET transistors. The input signal inputted to the differential input stage and converted from differential to single signal is amplified by transistor M7 with gate grounded, and further amplified by transistor M1.
The signal is inverted and amplified at O and output to output terminal 3. Transistors M6 and M8 operate as a load B and a constant current source for transistor M7, respectively. Transistor MR and capacitance C
As in FIG. 2, the one-frequency compensation circuit consisting of C is connected between the output terminal 3 and the output terminal of the differential stage of transistors Ml and M2, but the transistor M9, which is the load of the output stage, Since the transistor M9 is not connected between the gate and drain of the transistor M9, even if the frequency compensation circuit becomes low impedance at high frequencies, the transistor M9 will not be in a diode-connected form, and power supply noise will easily enter through the transistor M9. That's not the case. Therefore, the power supply and noise rejection ratios do not deteriorate at high frequencies, and a good power supply noise rejection ratio can be obtained.

In addition, in FIG. 3, the signal from the differential pair is input to the output stage via the source follower, inverted and amplified by the transistor M14, and outputted, but in the embodiment shown in FIG. The signal is amplified by the gate-grounded transistor M7, and is inverted and amplified again by the output stage transistor Ml□, so the gain is higher than in the case of Fig. 3 by the amplifier in transistor M7. Therefore, it is possible to increase the cost by several tens of times. Therefore, like the operational amplifier in Figure 3,
Compared to the operational amplifier of FIG. 2, the embodiment of FIG. 1 does not have a reduced gain, but rather an increased gain.

(Effects of the Invention) As described above, the operational amplifier of the present invention has the advantage that the power supply noise rejection ratio is good even at high frequencies, and the gain is sufficiently high (3).

[Brief explanation of drawings]

FIG. 1 is a circuit diagram of an embodiment of the present invention, and FIGS. 2, 2, and 3 are circuit diagrams of an example 2 and another example of a conventional operational amplifier, respectively. 1.2...Input terminal, 3...Output terminal, 4.5...Power line, 6-12...
・Bias terminal, M1 to M14. MR・・・・・・MO
8FET transistor, Cc... Capacity. Cow's second and third child

Claims (1)

[Claims] MISFE whose sources are commonly connected to the first constant current source
T differential pair, a first MISFET with a grounded gate whose source is connected to the output of the MISFET differential pair, and a second MISFET connected to the first MISFET and serving as a second constant current source. , a third MISFET serving as a first load connected to the first MISFET, and a fourth MISFET having a gate connected to the drain of the first MISFET.
a fifth MISFET connected to the fourth MISFET and serving as a second load; and an output terminal connected to the drain of the fourth MISFET and an output of the differential pair. An operational amplifier circuit comprising a frequency compensation circuit.