JPH0983270A - Band split amplifier circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain the band split amplifier circuit by which low distortion amplification is conducted by maximizing the effect of amplification of signals at each split band. SOLUTION: A low frequency component passing through a low pass filter 17 is subtracted from an input signal to cancel distortion. Furthermore, a high frequency component passing through a high pass filter 23 is subtracted from the input signal to cancel distortion. Moreover, 1st and 2nd preamplifiers 16, 22 are used to match an output impedance of a photo diode 12 and an input impedance of each filter. After low and high frequency signals are individually amplified by the amplifiers 21, 26 and the resulting signals are combined by a coupling circuit, which provides an output. A steep cut-off characteristic is obtained by feeding back negatively an output of each filter, the frequency bands are split almost completely and low distortion amplification is attained. Furthermore, the frequency characteristic within the pass band of each filter is made flat by impedance matching and low distortion is enhanced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a band division amplifier circuit that divides an input signal into two frequency bands, individually amplifies them, and then adds them together. In particular, an electric signal output from a light receiving element such as a photodiode. The present invention relates to a band division amplification circuit that amplifies a.

[0002]

2. Description of the Related Art In the field of optical communication, in order to improve transmission efficiency, an optical signal is usually intensity-modulated and transmitted by a modulation signal obtained by frequency-multiplexing a plurality of information signals. The receiving station receives the transmitted optical signal by a light receiving element such as a photodiode and converts the optical signal into an electric signal, and then amplifies the signal with an amplifier. In general, in an amplifier that amplifies an electric signal, the greater the number of signals frequency-multiplexed with the input signal, the more distortion the output signal has. Therefore, the receiving station divides the electric signal output from the light receiving element into two frequency bands, a high frequency band and a low frequency band, amplifies each frequency band, and then adds them together.
Such an amplifier circuit that amplifies the input signal by dividing it into a plurality of frequency bands will be referred to as a band division amplifier circuit.

FIG. 3 shows the configuration of a band division amplifier circuit that has been conventionally used in an optical signal receiving station. Optical signal 101 transmitted through an optical fiber
Is received by the photodiode 102 and converted into a current signal 103 corresponding to the intensity of light. The current signal 103 output from the photodiode 102 is branched into two and input to the low-pass filter 104 and the high-pass filter 105, respectively. The low pass filter 104 passes a frequency component of the current signal 103 lower than a preset separation frequency. On the other hand, the high-pass filter 105 passes a frequency component higher than the separation frequency in the current signal 103.

The output signal of the low-pass filter 104 is amplified by the first preamplifier 106 and the first amplifier 107, respectively. The output signal of the high-pass filter 105 is amplified by the second preamplifier 108 and the second amplifier 109, respectively. The output signal of the first amplifier 107 and the output signal of the second amplifier 109 are input to the combining circuit 111 that adds them up. In this way, the frequency band is divided into two with the separation frequency as a boundary, and each band is amplified by an individual amplifier, so that the distortion generated in the amplifier can be reduced.

JP-A-57-171809 discloses a band division amplifier circuit in which an audio signal is frequency-divided into a high band and a low band, and power amplification of the audio signal is performed by an amplifier circuit of a system suitable for each band. Is disclosed.
In this circuit, a low frequency band in which energy consumption is concentrated is amplified by a high efficiency and low distortion PWM (pulse width modulation) type amplifier. In addition, in the high frequency band, although the efficiency is low, the acoustic characteristics such as the distortion rate are excellent.
It is amplified with a class B or class B amplifier. By dividing the audio signal into two frequency bands and individually amplifying them by an amplifier circuit of a system suitable for each band, it is possible to perform power amplification with high efficiency and low distortion.

[0006]

In order to divide an electric signal to be amplified into a high frequency band and a low frequency band,
Usually, a low-pass filter and a high-pass filter in which capacitors and coils are combined in multiple stages are used. At this time, if there is a mismatch between the output impedance of the signal input to the filter and the input impedance of the filter, peaks and valleys will occur in the frequency characteristics in the pass band of the filter, resulting in flatness. No longer. In addition, if there is an impedance mismatch, reflection occurs at the input stage of the filter and the passage loss increases. In particular, a light receiving element such as a photodiode is likely to cause impedance mismatch with the filter because of its high output impedance. Therefore, there is a problem that the amplitude characteristic and the noise characteristic at the output of the filter are deteriorated, and the characteristics of the band amplification circuit as a whole are deteriorated.

Further, in a filter constituted by combining a capacitor and a coil, the maximum frequency that can be amplified is limited by the wiring length. Since the optical signal often includes a high frequency component of several gigahertz, it is necessary to reduce the order of the filter. As a result, the amount of attenuation outside the pass band of the filter cannot be secured sufficiently, and the high frequency component leaks into the low frequency side amplifier and the low frequency component leaks into the high frequency side amplifier. There is a problem of reducing the amplified effect.

Therefore, an object of the present invention is to provide a band division amplification circuit capable of maximizing the effect of dividing and amplifying a band and performing amplification with low distortion.

[0009]

According to a first aspect of the present invention, first subtracting means for subtracting a first feedback signal from an input signal having a predetermined frequency bandwidth, and an output of the first subtracting means. Low-pass filtering means for passing a frequency component lower than a predetermined separation frequency in the signal, second subtracting means for subtracting the second feedback signal from the input signal, and output of the second subtracting means High-pass filtering means for passing a frequency component higher than the separation frequency in the signal, first feedback signal branching means for taking out a part of the output signal of the low-pass filtering means as a second feedback signal, and high-pass filtering means. The second feedback signal branching means for extracting a part of the output signal of the filtering means as the first feedback signal, the first amplifying means for amplifying the output signal of the low-pass filtering means, and the high-pass filtering means. Second amplification means for amplifying the output signal, and first amplification means And it is provided in the band-splitting amplifier circuit and a signal combining means adding the output signal of the output signal and the second amplifying means.

That is, according to the first aspect of the invention, since a part of the frequency component lower than the separation frequency passed through the low-pass filtering means is subtracted from the input signal by the second subtractor, the high-pass filtering means In the previous stage, low frequency components are removed to some extent. As a result, the cutoff characteristic of the output signal of the high-pass filtering means becomes steeper than the cutoff characteristic of the high-pass filtering means itself. Further, since the first subtractor subtracts a part of the frequency component higher than the separation frequency that has passed through the high-pass filtering means from the input signal, the cut-off characteristic of the output signal of the low-pass filtering means is also filtered. It becomes steeper than the cutoff characteristic of itself. By constructing the feedback loop, this action is gradually strengthened, so that when the stable state is reached, the outside of the pass band can be almost completely attenuated. As a result, the frequency components of the signals input to the respective amplifiers are completely separated, and low distortion amplification can be performed.

According to the second aspect of the present invention, the first subtraction means for subtracting the first feedback signal from the input signal having the predetermined frequency bandwidth and the output signal of the first subtraction means are predetermined. Low-pass filtering means for passing a frequency component lower than the separation frequency, the low-pass filtering means, and
Of the second subtraction means, a first impedance matching means that is provided between the subtraction means of the first impedance matching means for matching impedance between them, a second subtraction means that subtracts the second feedback signal from the input signal, and A high-pass filtering means for passing a frequency component higher than the separation frequency in the output signal, and a second high-pass filtering means provided between the high-pass filtering means and the second subtracting means for matching impedance between them. Impedance matching means, first feedback signal branching means for extracting a part of the output signal of the low-pass filtering means as a second feedback signal, and part of the output signal of the high-pass filtering means for the first feedback signal The second feedback signal branching means, the first amplifying means for amplifying the output signal of the low-pass filtering means, the second amplifying means for amplifying the output signal of the high-pass filtering means, and the first The output signal of the amplification means and the second amplification means And a signal combining means sums the force signal is provided to a band splitting amplifier.

That is, according to the second aspect of the invention, the impedance matching means is arranged between the subtracting means and the filtering means. Therefore, peaks and valleys are less likely to occur in the pass characteristic of each filtering means, and the reflection at the input part of the filtering means is reduced, so that amplification can be performed with high efficiency and low distortion.

According to the third aspect of the invention, the signal level of the first feedback signal extracted by the first feedback signal branching means is equal to the signal level in the frequency component lower than the separation frequency of the input signal, The signal level of the second feedback signal extracted by the feedback signal branching means is equal to the signal level of the frequency component higher than the separation frequency of the input signal.

That is, according to the third aspect of the invention, the signal level fed back to the subtracting means is set equal to the level of the input signal. As a result, the frequency component outside the pass band of the filtering means can be canceled out from the input signal and almost completely removed.

According to the fourth aspect of the invention, the signal output from the photoelectric converter for converting the optical signal into the analog electric signal according to the intensity is used as the input signal of the band division amplifier circuit.

That is, in the invention described in claim 4, the current signal output from the photoelectric converter such as a photodiode is used as the input signal of the band division amplifier circuit. In particular, since the output impedance of the photodiode is high, it is necessary to make impedance matching with the filter. Further, the optical signal is often modulated at a high frequency of about several gigahertz. If the output of the filtering means is fed back to the subtracting means, a steep cutoff characteristic can be obtained even if the order of the filtering means composed of a capacitor and a coil is reduced. Since the order of the filtering means is reduced and the maximum frequency is less likely to be restricted by the wiring length, the frequency band in which amplification is possible can be widened.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows an outline of the configuration of a band division amplifier circuit according to an embodiment of the present invention. Here, the output signal from the photodiode that receives the optical signal is amplified by the band division amplifier circuit. Optical signal 11 sent from the transmitting station through the optical fiber
Is incident on the photodiode 12. The photodiode 12 outputs a current signal 13 having a magnitude corresponding to the intensity of the received light. The current signal 13 is output to the first subtractor 14
Are input to the second subtractor 15, respectively. The output signal of the subtractor 14 is amplified by the first preamplifier 16 that performs inverting amplification, and then input to the low-pass filter 17. The low-pass filter 17 is a circuit that passes a frequency component lower than a preset separation frequency.

The signal that has passed through the low-pass filter 17 is input to the first branch circuit 18. First branch circuit 18
Is a circuit that divides the output signal of the low-pass filter by two resistors (not shown). First flowing through one resistor
The feedback signal 19 of is input to the second subtractor 15. The second subtractor 15 subtracts the first feedback signal 19 from the current signal 13 from the photodiode 12. The current flowing through the other resistor of the first branch circuit 18 is input to the low frequency signal amplifier 21.

The output signal of the second subtractor 15 is amplified by the second preamplifier 22 which performs inverting amplification, and then input to the high-pass filter 23. The high-pass filter 23 passes a frequency component higher than the separation frequency. The signal that has passed through the high-pass filter 23 is input to the second branch circuit 24 and split. The second branch after being divided by the second branch circuit 24
The feedback signal 25 of is input to the first subtractor 14. The first subtractor 14 outputs a signal obtained by subtracting the second feedback signal 25 from the current signal 13.
The output current flowing through the other resistor of the second branch circuit 24 is input to the high frequency signal amplifier 26.

Both the high-frequency signal amplifier 26 and the low-frequency signal amplifier 21 are inverting amplifier circuits. The signals whose phases are once inverted by the preamplifiers 16 and 22 are returned to their original phases by the low frequency signal amplifier 21 and the high frequency signal amplifier 26. The output signal 27 of the low frequency signal amplifier 21 and the output signal 28 of the high frequency signal amplifier 26 are
Both are input to the coupling circuit 29. The coupling circuit 27 is
It is an adder circuit that takes the sum of these output signals 27 and 28.
The output signal 31 of the coupling circuit 29 is input to a circuit in the subsequent stage (not shown) as an output signal of the band division amplification circuit.

The first and second subtractors 14 and 15 are provided with a current signal from the photodiode 12 and branch circuits 18 and 2, respectively.
The feedback signals 19 and 25 from 4 are merged via resistors, respectively. Since the phases of the feedback signals 19 and 25 are inverted by the preamplifiers 16 and 22,
Subtraction can be done by simply joining. Further, the low-pass filter 17 and the high-pass filter 23 are general filter circuits in which capacitors and coils are combined, and the order of each is one stage. First,
The second preamplifiers 16 and 22, the low-frequency signal amplifier 21, and the high-frequency signal amplifier 26 are inverting amplifier circuits each composed of an operational amplifier and a resistor. The coupling circuit 29 has a configuration in which a signal line through which an output signal 27 of the low frequency signal amplifier 21 and an output signal 28 of the high frequency signal amplifier 26 flow is connected to each other via a resistor.

The signal levels of the first and second feedback signals 19 and 25 output from the first and second branch circuits 18 and 24 are equal to the signal level of the current signal 13.
That is, the amplification gain of the first preamplifier 16 is set to "GL".
Then, the signal level of the first feedback signal 19 is 1 / “GL” of the output signal of the low-pass filter 17. Similarly, when the amplification gain of the second preamplifier 22 is “GH”, the signal level of the second feedback signal 25 is set to 1 / “GH” of the output signal of the high-pass filter 23. ing. By subtracting the first feedback signal 19 having such a signal level from the current signal 13 by the second subtractor 15, frequency components lower than the separation frequency included in the current signal 13 are canceled. Similarly, the first subtractor 14 subtracts the second feedback signal 25 from the current signal 13 to almost completely cancel the frequency components higher than the separation frequency. Therefore, a steep cutoff characteristic can be obtained without increasing the orders of the low-pass filter 17 and the high-pass filter 23.

The low-pass filter 17 and the high-pass filter 23
Has a function of removing frequency components outside the pass band, and a function of stabilizing the operation of dividing the frequency band at an early stage when the circuit is activated. In addition, the first,
The second preamplifier 16, 22 acts as an impedance matcher. Since these preamplifiers 16 and 22 are composed of operational amplifiers, their output impedance is low. Filter 1 composed of capacitor and coil
Since the input impedances of 7 and 23 are relatively low, impedance matching can be achieved by arranging the preamplifiers 16 and 22 in front of the filters 17 and 23. By matching the impedance, it is possible to prevent the occurrence of peaks or troughs in the frequency characteristics within the pass band of the low-pass filter 17 and the high-pass filter 23. Further, since the reflection at the input end of the filter is unlikely to occur, the pass loss in the pass band can be reduced.

Here, the separation frequency is set to a value that minimizes the distortion generated in the amplifier for each band in consideration of the frequency component contained in the optical signal. Here, the frequency band of the signal included in the optical signal is 1 GHz,
The separation frequency is set to 500 MHz, which is just half the band.

FIG. 2 shows an example of the frequency spectrum of the signal of each part of the band division amplifier circuit shown in FIG. In the figure, the horizontal axis represents frequency and the vertical axis represents power. The frequency spectrum of the current signal 13 output from the photodiode 12 (a in the figure) is substantially evenly dispersed in the frequency band 41 of about 1 GHz. Second
The frequency spectrum of the second feedback signal 25 obtained from the branch circuit 24 of FIG. 2 (b in the figure) has only frequency components higher than the separation frequency shown by the arrow 42. First subtractor 1
The frequency spectrum of the output signal of No. 4 (FIG. 7C) is the rest of the current signal 13 after subtracting the second feedback signal 25, that is, only the frequency component lower than the separation frequency 42.

The signal waveform (FIG. 2D) after the output signal of the first subtractor 14 is amplified by the first preamplifier 16 is shown in FIG.
The power of each frequency spectrum component is increased as compared with c. The dotted line 43 indicates the first subtractor 14 and the low-pass filter 17
It shows the filtering characteristics when these are combined. Of the first feedback signal (e in the figure) obtained from the first branch circuit 18,
The signal level matches the signal level of the current signal 13 (a in the figure). The output signal of the low-frequency signal amplifier 21 (f in the figure) is amplified by the remaining current signal branched by the first branch circuit 18, and its signal level is increased.

Output signal of the second subtracter 15 (g in FIG. 3)
Is obtained by subtracting the first feedback signal (e in the figure) from the current signal 13 (a in the figure). That is, there are only frequency components higher than the separation frequency. The output signal of the second preamplifier 22 (FIG. 2H) has the power of each frequency component increased as compared with FIG. 2G. Dotted line 44 in the figure
Represents the filtering characteristic when the second subtractor 15 and the high-pass filter 23 are combined. The second feedback signal obtained by the shunt in the second branch circuit 24 has the waveform shown in FIG. The signal amplified by the high-frequency signal amplifier 26 (i in the figure) is combined with the output signal of the low-frequency signal amplifier 21 (f in the figure) by the coupling circuit 29, so that the frequency spectrum of the output signal (the same figure) Similarly to the current signal 13 from the photodiode 12, j) is evenly spread within the frequency band of 1 GHz.

By subtracting a feedback signal, which is a signal having an opposite phase of the frequency band to be removed by the filter, from the input signal by the subtractor, the cutoff characteristic of the filter itself is not steep. Good. For example, it is assumed that the attenuation characteristic near the separation frequency of the signal component that has passed through the low-pass filter is -3 dB (decibels) / oct (octave). When the remaining signal component obtained by subtracting this from the input signal is attenuated by -3 dB / oct by the high-pass filter, overall,
It becomes -6db. When this is fed back to the first subtractor,
High frequency components are removed with a characteristic of -6 dB / oct.
This signal is further -3 dB / oct by the low pass filter.
The attenuation characteristic of the first feedback signal is -9d.
increase to b / oct. Since the feedback loop is configured in this way, the cutoff characteristics gradually become steeper,
When the stable state is reached, it is possible to completely attenuate the outside of the pass band at the boundary of the separation frequency. Therefore, since it is not necessary to make the cutoff characteristics of the low-pass filter 17 and the high-pass filter 23 themselves steep, the order of the filter can be reduced and the maximum frequency is less likely to be limited by the wiring length.

In the embodiment described above, the output current of the photodiode is branched, but the current may be supplied from the input terminal and the output terminal of the photodiode to each subtractor. When performing non-inverting amplification with the preamplifier, the subtractor may be composed of an operational amplifier. At this time, the current signal from the photodiode is applied to the non-inverting input,
A feedback signal will be input to the inverting input. Further, when an operational amplifier is used as the subtractor, impedance matching can be achieved by this operational amplifier, so that it is not necessary to dispose a preamplifier. Further, in the embodiment, each signal is amplified as a current signal, but may be filtered or amplified as a voltage signal.

[0030]

As described above, according to the first aspect of the present invention, the low frequency signal and the high frequency signal can be almost completely separated centering on the separation frequency, and amplification with low distortion can be performed. Further, even if the order of the filtering means is small, a steep cutoff characteristic can be obtained, so that the maximum frequency is less likely to be restricted by the wiring length of the filtering means, and the amplifiable frequency band can be widened. it can.

According to the second aspect of the invention, since the impedance matching means is arranged between the subtracting means and the filtering means, peaks and valleys are less likely to occur in the pass characteristics of each filtering means, and the filtering means is provided. The amount of reflection at the input part of is reduced, and amplification can be performed with high efficiency and low distortion.

Further, according to the third aspect of the present invention, since the signal level fed back to the subtracting means is made equal to the level of the input signal, the frequency components outside the pass band are canceled out from the input signal and are almost completely removed. be able to.

According to the fourth aspect of the invention, the current signal output from the photoelectric converter such as a photodiode is used as the input signal of the band division amplifier circuit. In particular, since the output impedance of the photodiode is high, the frequency characteristics in the pass band can be made flat by performing impedance matching with the filter. In addition, an optical signal is often modulated at a high frequency of about several gigahertz, but a steep cutoff characteristic can be obtained by a filtering means of a small order, so that the maximum frequency is limited by the wiring length of the filtering means. It becomes difficult to receive, and the frequency band which can be amplified can be widened.

[Brief description of drawings]

FIG. 1 is a block diagram showing an outline of a configuration of a band division amplifier circuit according to an embodiment of the present invention.

FIG. 2 is a waveform diagram showing an example of a frequency spectrum of a signal of each part of the band division amplification circuit shown in FIG.

FIG. 3 is a block diagram showing a configuration of a band division amplifier circuit which has been conventionally used.

[Explanation of symbols]

 11 Optical Signal 12 Photodiode 14, 15 Subtractor 16, 22 Preamplifier 17 Low-pass Filter 18, 24 Branch Circuit 21 Low-frequency Signal Amplifier 23 High-pass Filter 26 High-frequency Signal Amplifier 29 Coupling Circuit 42 Separation Frequency

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI technical display location H04B 10/14 10/04 10/06

Claims (4)

[Claims] 1. A first subtraction means for subtracting a first feedback signal from an input signal having a predetermined frequency bandwidth, and an output signal of the first subtraction means having a frequency lower than a predetermined separation frequency. Low-pass filtering means for passing a frequency component, second subtracting means for subtracting a second feedback signal from the input signal, and a frequency component higher than the separation frequency in the output signal of the second subtracting means A high-pass filtering means, a first feedback signal branching means for extracting a part of the output signal of the low-pass filtering means as the second feedback signal, and an output signal of the high-pass filtering means. Second feedback signal branching means for extracting a part as the first feedback signal, first amplifying means for amplifying an output signal of the low-pass filtering means, and amplifying an output signal of the high-pass filtering means. Of the second amplifying means and the first amplifying means Force signal and band dividing amplifier circuit, characterized by comprising a signal combining means for adding the output signal of the second amplifying means. 2. A first subtracting means for subtracting a first feedback signal from an input signal having a predetermined frequency bandwidth, and an output signal of the first subtracting means which is lower than a predetermined separation frequency. Low-pass filtering means for passing a frequency component, first impedance matching means provided between the low-pass filtering means and the first subtracting means for matching impedance between them, and Second subtracting means for subtracting the second feedback signal from the input signal; high-pass filtering means for passing a frequency component higher than the separation frequency in the output signal of the second subtracting means; Second impedance matching means provided between the filtering means and the second subtracting means for matching impedance between them, and a part of the output signal of the low-pass filtering means for the second feedback. Take out as a signal A first feedback signal branching means, a second feedback signal branching means for extracting a part of the output signal of the high-pass filtering means as the first feedback signal, and an output signal of the low-pass filtering means. A first amplifying means for amplifying, a second amplifying means for amplifying an output signal of the high-pass filtering means, and a signal for adding an output signal of the first amplifying means and an output signal of the second amplifying means. A band division amplification circuit comprising: a coupling means. 3. A signal level of the first feedback signal taken out by the first feedback signal branching means is equal to a signal level in a frequency component of the input signal lower than the separation frequency, and the second feedback is provided. The band division amplification according to claim 1 or 2, wherein the signal level of the second feedback signal taken out by the signal branching means is equal to the signal level in a frequency component higher than the separation frequency of the input signal. circuit. 4. The band division amplifier circuit according to claim 1, wherein the input signal is an output signal of a photoelectric converter for converting an optical signal into an analog electric signal according to its intensity. .