JPH03216006A - Amplifier - 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 device used as a preamplifier device for optical communications.

[Conventional technology]

Conventionally, in optical communication, an optical signal is received by a photodiode (not shown) as shown in FIG.
A signal voltage V is obtained from the output terminal 3 by amplifying the signal. The amplifier 2 is a so-called single-ended transimpedance type amplifier in which a feedback out resistor Rr is externally attached or integrated. This amplifier 2, as shown in more detail in FIG.
It is equipped with an amplifier circuit 21 that constitutes an amplification stage for amplifying a signal, and a buffer circuit 22 that constitutes an output buffer stage together with an output impedance R connected to the output terminal 3 after the amplifier circuit 21. be. A conventional example (A) is known in which a feedback resistor R is connected between the input terminal 1 and the output terminal of the amplifier circuit 21.

Further, as another detailed example of the amplifier 2, as shown in FIG. 6, although it has almost the same configuration as the circuit shown in FIG. A conventional example (B) in which a connection is made between the two is also known.

Among the above conventional examples, an amplifier having the configuration of the conventional example (A) is, for example, the FMM321, which is a product of Fujitsu Limited.
It is known as CP, and its circuit configuration is as shown in FIG.

The circuit shown in FIG. 7 includes an amplification stage consisting of FETQ1 and resistor R1, a level shift stage consisting of FETQ14 and FETQ12, and FETQ13 and FETQ1.
The output buffer stage consisting of 5 and 5 are driven by the same power supply vs8. Also, 12' of FETQ Q
13 The drain side is grounded. A load resistor R1 is connected between the drain of FETQ11 and ground.

The diodes D and D connected to the sources of FETQ and Q are for level shifting.
1 12 and has a function of determining a predetermined bias point. In addition, FET Q Q has gate conflict between source and source 14'
15 is short-circuited and functions as a constant current load. According to the circuit having such a configuration, an input signal can be amplified by an amplification factor (A) and an inverted output signal V can be obtained.

When the above-mentioned conventional amplifier device is used as a preamplifier for an optical receiver, the total input capacitance including the photodiode capacitance etc. is C. Assuming that the load impedance is In RL and that the amplifier band is sufficiently wide,
The transimpedance and band are shown in Table 1 below.

\ \ \ \ \ \ \ [Problem to be solved by the invention] However, the above-mentioned prior art (A). In the amplifier of (B), the output impedance R. is normally designed to be 50Ω. Therefore, when the load impedance RL changes, first of all, the transimpedance changes greatly in the conventional technology (A) amplifier, and the band changes greatly in the conventional technology (B) amplifier.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide an amplifier device that can suppress changes in transimpedance and band even when load impedance changes, and can therefore achieve substantially stable characteristics regardless of the load.

[Means to solve the problem]

The amplifier device according to the present invention includes: an amplifier circuit that constitutes an amplification stage that amplifies an input signal arriving from an input terminal; a buffer circuit that is connected to the subsequent stage of this amplifier circuit and constitutes an output buffer stage that performs impedance conversion; a first feedback resistor connected between the output terminal of the circuit and the input terminal;
The present invention is characterized by comprising a second feedback resistor connected between the output terminal of the buffer circuit and the input terminal.

[Effect]

According to the amplifier having the above configuration, the values of the first and second feedback resistors are R and R, and the transformer f'l
The f'2 waveband and band are expressed as follows.

Transimpedance; AIXA2XRtlXR
X (R / (R + R )) / [R, lXf'
2 L O L (1+
A XA XR / (Ro+RL)}+12
L R r 2 X < t + A t )]
・・・・・・(1) Band; L/2πX
[R X { 1 + A XA2 Xfl
l R /(R + R)}+Rr2X(1+A1)
]L OL / (R,,XRf2XCin) −
------- (2) Comparing the above formula with the formula in Table 1, the transimpedance formula is close to the formula of the conventional example (B), and the band formula is similar to the numerator of the formula of the conventional example (B). It can be seen that a term that is not affected by the load impedance RL is added, and the fluctuations in both cases are reduced with respect to changes in the load impedance RL.

? Examples] Below, Figures 1 to 3 and Figures 8 and 9 of the attached drawings are shown.
An amplifier device according to an embodiment of the present invention will be described with reference to the drawings.

FIG. 1 shows an amplifier device according to an embodiment of the present invention. An input signal arriving from the input terminal 1 is inverted and amplified by an amplification factor (A1) by an amplification circuit 101 that constitutes an amplification stage, and is sent to a buffer circuit 102 that constitutes an output buffer stage.

The buffer circuit 102 performs impedance conversion, amplifies the signal with an amplification factor (A2), and outputs the signal from the output terminal 3 via the output impedance Ro. In addition, the amplifier circuit 101
A feedback resistor R, ■ is connected between the output terminal and input terminal 1. Furthermore, a feedback resistor R'2 is connected between the input terminal 1 and the output terminal 3. As a result, it is possible to realize the transimpedance according to equation (1) and the band according to equation (2), and it is possible to reduce fluctuations in response to changes in load impedance compared to the conventional method.

FIG. 2 shows a circuit diagram embodying the amplifier device of FIG. 1 using FETs. In this circuit, FETQ. The input signal is inverted and amplified by Q12. The level shift diode D 1 has the function of lowering the signal output to the 1 source of FET Q3 to a predetermined potential. The signal flowing through the level shift diode D1 is applied to FETQ, which serves as a constant current load. The signal from the drain of FETQ4 is applied to the gate of FETQ5, where impedance conversion is performed to reduce the output impedance.
An output signal is sent to the output terminal 3 from the connection point with the drain. Further, the drain of the FETQl is connected to the FETQ2, which is a constant current load whose gate and source are short-circuited.

The source of FETQ is grounded and FETQ, Q3,
12 The drain of Q5 is given voltage vDD from the power supply, and F
A voltage vs846 is applied to the sources of ETQ and Q from the power supply. Feedback resistor Rr1 connects input terminal 1 and FE
The feedback resistor R,2 is connected between the input terminal 1 and the output terminal to form a transimpedance type amplifier.

In this example, the threshold voltages of FETQt~Q6 are all -1v, and each FE
The gate width of T is 150μm, 75μm, 50μm, 5
04 m, 150 um, and 150 μm. Feedback resistance Rf
The resistance value of l is 7KΩ, and the resistance value of feedback resistor Rf2 is 4KΩ.
And so. For comparison, a conventional example (A
), and a conventional example (B) in which only the feedback resistor Rf2 is connected, the characteristic curve was obtained by calculating the transimpedance and the band.The characteristic white line of this example is shown in Fig. 3. The characteristic curve of example (A) is placed in the 8th section of the conventional example (
The characteristic curves of B) are shown in FIG. Two examples are shown in which the capacitance of the photodiode is 0.65 pF and the load impedance is 50Ω and 500Ω. To summarize this calculation result, from this calculation result, the load impedance can be changed from 50Ω to 5Ω.
00Ω, the value of the transimpedance in the conventional technology (A) changes greatly by 1.58 times, and in the conventional technology (B) the band changes by 1.53 times, but in this example, the value of the transimpedance changes significantly. is 1.28 times, and the bandwidth is 1.
We were able to keep the change to only 26 times.

〔Effect of the invention〕

As described in detail above, according to the present invention, by using two feedback resistors to couple between the input and output terminals and between the input and output terminals of the amplifier circuit, fluctuations in transimpedance and band can be reduced to load impedance. It is possible to realize almost stable characteristics, which can widen the selection range of load impedance.

[Brief explanation of drawings]

FIG. 1 is a block diagram of an embodiment of the present invention, FIG. 2 is a circuit diagram of an amplifier according to an embodiment constructed using FETs, and FIG.
The figure shows the frequency response characteristics of the circuit in figure 2,
7 to 7 are block diagrams of conventional amplifier devices, and FIG.
9 and 9 are diagrams showing frequency response characteristics of conventional circuits, 1...input terminal, 3...output terminal,
101...Amplification circuit, 102...Buffer circuit, R
o...Output impedance, R, R...Feedback resistance, Q-06...Ff'l f'2
1ET, Dl - Level shift diode.

Claims (1)

[Scope of Claims] An amplifier circuit constituting an amplification stage that amplifies an input signal arriving from an input terminal; a buffer circuit constituting an output buffer stage that is connected to a subsequent stage of this amplification circuit and performs impedance conversion; and the amplification circuit. A first feedback resistor connected between the output terminal of the buffer circuit and the input terminal, and a second feedback resistor connected between the output terminal of the buffer circuit and the input terminal. An amplification device for