JPH0468805A - amplifier circuit - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an amplifier circuit, and particularly to a transimpedance amplifier circuit.

[Conventional technology]

Transimpedance amplifier circuits with excellent frequency characteristics are often used to amplify the output power of various sensors.

FIG. 4 shows a conventional example of a pin photodiode receiver using this transimpedance amplifier circuit. In the same figure, reference numeral 51 is a pin photodiode, 52 is a transistor which is an active element for amplification, 53 is a load element which is a transistor whose gate and source are short-circuited, and 54, 58, 59 are terminals for power supply. 55 is a source follower transistor, 56 is a level shift element, 57 is a transistor whose gate and source are short-circuited, 60 is an output terminal, and 61 is a feedback resistor.

The feature of this conventional circuit is that the level-shifted output signal is applied to the amplifying active element 52 as an opposite phase feedback signal via a feedback resistor 61.

This feedback signal lowers the input impedance and p
High-speed operation is possible even when using a sensor with high output impedance such as an in-photodiode.

[Problem to be solved by the invention]

However, such conventional transimpedance amplifier circuits use a level shift circuit that has a delay property in signal propagation, so there is a problem that the feedback signal is delayed in the case of a high-speed signal. As a result, the frequency characteristics rise as shown in FIG. 5(a), the output signal overshoots as shown in FIG. 5(b), etc., which adversely affect the receiver characteristics.

[Means to solve the problem]

In order to solve the above problem, in the amplifier circuit of the present invention, a feedback circuit constituted by a series circuit of a resistor and a capacitor is connected between the output terminal of the load element and the input terminal of the active element for amplification. .

[Effect]

With the configuration of the present invention, since the feedback circuit is provided between the output terminal of the load element and the input terminal of the active element for amplification, the feedback signal without delay due to the level shift circuit is transmitted to the output terminal of the load element. is applied directly to the active element for amplification. At this time, since a capacitor is provided in the feedback circuit, it does not affect the DC bias of the input signal source.

〔Example〕

Hereinafter, one embodiment of the present invention will be described with reference to FIG. 1 of the accompanying drawings.

FIG. 1 shows a pin photodiode receiver using a transimpedance amplifier circuit, which is an embodiment of the present invention. All transistors used in this example are field effect transistors. input signal source pin
The anode of the photodiode 11 is connected to the gate of a transistor 12 which is an active element for amplification, and the drain of the transistor 12 is connected to the transistor 1 which is a load element.
Connected to 3 sources. In addition, the transistor 12
The source of the transistor 13 is connected to a power supply terminal 14 to which an intermediate voltage power supply V is applied.
The drain of is the power supply terminal 1 to which the high voltage power supply vDD is applied.
9 is connected. The gate of the transistor 13 is connected to the source follower transistor 15 and the level shift element 16.
and a transistor 17, and the source of the transistor 17 is connected to a power supply terminal 20 to which a low voltage power supply V 1 is applied. An output terminal 21 and a feedback resistor 22 are connected to the drain, and the other end of the feedback resistor 22 is connected to the gate of the transistor 14 .

Furthermore, the gate of transistor 12 and the gate of transistor 13
A feedback circuit 23 is connected between the sources of , and this feedback circuit 23 is composed of a capacitor 24 and a resistor 25 .

Next, the operation of this embodiment will be explained.

The pin photodiode 11 converts light into an electrical signal, and this electrical signal is applied to the gate of the transistor 12. In the transistor 12, the drain current changes according to this input signal, and as this drain current flows through the load transistor 13, a voltage that is an amplified input signal is generated at the drain of the transistor 12. This signal voltage is applied to the gate of source follower transistor 15, level-shifted by source follower transistor 15 and level shift element 16, and appears at output terminal 21.

This embodiment differs from the conventional example in that two types of feedback signals passing through different feedback paths are applied to the transistor 12 described above. The first feedback signal is an opposite phase signal applied via the feedback resistor 22. The second feedback signal is
This is a signal applied from the source of the transistor 13 via the feedback path 23.

In the conventional example, the output signal was applied to the transistor 12 via the feedback resistor 22, but this feedback signal was delayed due to the influence of the level shift circuit 18.

This delay in the feedback signal caused the frequency characteristics to rise and the output signal to overshoot as shown in FIGS. 5(a) and 5(b).

Therefore, in this embodiment, in addition to the conventional feedback path, a second feedback path is provided between the gate of the transistor 12 and the source of the transistor 13 by a feedback circuit 23. According to this second feedback path, a signal in phase with the output signal is applied to the transistor 12 without passing through the level shift circuit 18 having a delay property. Therefore, even for high-speed signals, an appropriate amount of feedback determined by the resistor 25 is performed, and FIGS. 2(a) and 2(b)
) It is possible to construct an amplifier circuit that exhibits good characteristics as shown in FIG.

As an application example of this embodiment, FIG. 3 shows a circuit having a gate grounding circuit in the middle. In addition to this application example,
The present invention is also applicable to a circuit having a configuration including a plurality of amplifiers.

In this embodiment, a field effect transistor is used for each transistor, but the same effect can be obtained even if a bipolar transistor is used.

Further, the resistance value of the resistor 25 is 0 of the resistance value of the feedback resistor 22.
, 5 to 2.0 times.

The reason for this is that if the value of the feedback resistor 22 is too large, the effect of the present invention will be significantly reduced, while if it is too small, the amount of feedback will become too large, leading to band deterioration of frequency characteristics.

〔Effect of the invention〕

As explained in detail above, according to the amplifier circuit of the present invention, it is possible to secure an appropriate amount of feedback for high-speed signals and high-frequency signals without raising the frequency characteristics or overshooting the output signal. , a transimpedance amplifier circuit with good characteristics can be constructed.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram of a transimpedance amplifier circuit according to an embodiment of the present invention, FIG. 2 is a waveform diagram of the transimpedance amplifier circuit of FIG. 1, and FIG. 3 is a transimpedance amplifier circuit of an application example of the present invention. 4 is a circuit diagram of a conventional transimpedance amplifier circuit,
FIG. 5 is a waveform diagram of the transimpedance amplifier circuit of FIG. 4. 11...pin photodiode, 12.13.17
...Transistor, 14.19.20...Power supply terminal, 15...Source follower transistor, 16...
Level shift element, 18... Level shift circuit, 2
1... Output terminal, 22... Feedback resistor, 23... Feedback circuit, 24... Capacitor, 25... Resistor. Figure 1

Claims (1)

[Claims] An active element for amplification whose current is controlled by an input signal, a load element connected in series to this active element for amplification and for taking out the output current as a voltage, and a voltage obtained by this load element. In a transimpedance amplifier circuit comprising a level shift means for level shifting a signal voltage, and a feedback resistor connected between an output terminal of the level shift means and an input terminal of the amplification active element, the output terminal of the load element and an input terminal of the active element for amplification, a feedback circuit constituted by a series circuit of a resistor and a capacitor is connected between the input terminal and the input terminal of the active element for amplification.