JP3437344B2 - Waveform shaping circuit - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a waveform shaping circuit, and more particularly to a waveform shaping circuit for shaping a received signal waveform of a pulse signal train. This type of circuit is used in a 3R repeater or a terminal station of an optical communication system or the like for amplifying and shaping a received waveform composed of a pulse signal train.

[0002]

2. Description of the Related Art FIGS. 10 and 11 are diagrams (1) and (2) for explaining a conventional technique. Conventionally, by making the frequency characteristic of the receiving section close to the fifth-order Bessel Thomson filter characteristic (for example, f _C = 7GH _Z ) as shown in FIG. 10A, the output as shown in FIG. A signal eye pattern was realized.

[0003]

However, in recent years, especially in the trunk line optical communication system, a larger capacity, ultra-high-speed communication system is provided in order to cope with the advanced informationization of society such as moving image transmission and data transmission in the future. Is required. A frequency band characteristic corresponding to a transmission rate is required for a receiving unit of an ultrahigh-speed communication system, but it is becoming more and more difficult to realize a wideband characteristic as the signal rate increases.

Generally, when the band of the receiving section is insufficient, waveform interference occurs in the received waveform and the eye opening deteriorates. Figure 11
(A) and (B) are simulations of the deterioration of the eye opening when the frequency characteristic of the receiving unit is made insufficient to the fifth-order Bessel Thomson filter characteristic (for example, f _C = 5GH _Z ). Actually, such a technical problem is always faced, while further higher speed than that of FIG. 10 is required.

Further, the eye opening changes not only due to the shortage of the band of the receiving section, but also due to waveform deterioration due to the characteristics of the transmission line, temperature fluctuation of the transmitting / receiving section, deterioration over time, characteristic variation, and the like. An object of the present invention is to provide a waveform shaping circuit that can always obtain a good eye opening in a received waveform.

[0006]

[0007]

The above-mentioned problem is solved, for example, by referring to FIG.
It is solved by the configuration of. That is, the waveform shaping circuit of the present invention ( 1 ) is a waveform shaping circuit for shaping the signal waveform of a pulse signal train, wherein the first amplitude detection circuit 1 for detecting the amplitude of the input low-speed signal component and the input high-speed signal The second amplitude detection circuit 2 for detecting the amplitude of the component and the respective detection outputs V _P1 and V _P2 of the first and second amplitude detection circuits 1 and 2 are compared, and the ratio V
Control signal V _C such that _P2 / _VP1 becomes a predetermined value exceeding 1
And a control signal V of the comparison control circuit 3 having a peaking characteristic of the gain in the high frequency part of the required band.
_The gain frequency characteristic variable circuit 4 has a peaking characteristic variable with respect to an input signal by _C.

The above problem can be solved by, for example, the configuration shown in FIG. That is, the waveform shaping circuit of the present invention ( 3 ) is a waveform shaping circuit for shaping the signal waveform of a pulse signal train, wherein the first peak detection circuit 11 for detecting the peak level of the input signal and the high band part of the required band are provided. A gain-frequency characteristic variable circuit 4 having a gain peaking characteristic in which a peaking characteristic with respect to an input signal is variable by a control signal V _C ;
The second peak detection circuit 22 for detecting the peak level of the output signal of the gain frequency characteristic changing circuit 4 and the respective detection outputs V _P1 and V _P2 of the first and second peak detection circuits are compared, and the ratio V _P2 The comparison control circuit 3 generates the control signal V _C such that / V _P1 has a predetermined value exceeding 1.

The above problem can be solved by, for example, the configuration of FIG. That is, the waveform shaping circuit of the present invention ( 5 ) is a waveform shaping circuit that shapes the signal waveform of a pulse signal train, and the first peak detection circuit 11 that detects the peak level of the input signal and the input signal are input, A peaking circuit 21 having a gain peaking characteristic in a high frequency part of a required band.
And the second peak detection circuit 22 that detects the peak level of the output signal of the peaking circuit 21 and the respective detection outputs V _P1 and V _P2 of the first and second peak detection circuits 11 and 22, and the ratio thereof is compared. A comparison control circuit 3 for generating a control signal V _C such that V _P2 / V _P1 becomes a predetermined value exceeding 1, and a control signal for the comparison control circuit having a gain frequency cutoff characteristic in a high band portion of a required band. The frequency band variable circuit 5 is provided for controlling the gain of the output signal of the peaking circuit 21 by V _C in a frequency band limited manner.

[0010]

First, the principle of operation will be described with reference to FIG.
Generally, the amplitude of the high-speed signal component of the input pulse signal train is deteriorated due to the characteristics of the transmission line and the receiving unit {Fig. 1
(A)}. FIG. 1C shows an eye pattern of the input signal in this case, and if the eye opening becomes small as shown in the figure, an identification error is likely to occur in the identification unit in the subsequent stage.

Under such circumstances, the gain frequency characteristic circuit section 10
1 has a peaking characteristic in the high-frequency part of the required band as shown in FIG. 1D, and performs waveform shaping so that the amplitude of the high-speed signal component becomes larger than the amplitude of the input low-speed signal component due to the peaking characteristic. {Fig. 1 (b)}. Figure 1 (e)
Shows the eye pattern of the output signal in this case.As a result of adding overshoot and undershoot to the waveform of the high-speed signal component, an appropriate margin is generated in the eye opening, and an identification error occurs in the identification section in the subsequent stage. It gets harder.

By the way, the above configuration is suitable when the characteristics of the transmission line, the receiving section, etc. are fixed (constant), but in reality, these characteristics often vary. In such a case, it is necessary to adaptively change the peaking characteristic of the gain frequency characteristic circuit section 10. In this respect, in the waveform shaping circuit of the present invention ( 1 ) in FIG. 2, the first amplitude detection circuit 1 detects the amplitude of the input low-speed signal component, and the second amplitude detection circuit 2 detects the input high-speed signal. Detect the amplitude of the component.
The comparison control circuit 3 compares the detection outputs V _P1 and V _P2 of the first and second amplitude detection circuits 1 and 2, and a control signal V that makes the ratio V _P2 / V _P1 exceed a predetermined value. Generate _C. The variable gain frequency characteristic circuit 4 has a gain peaking characteristic in the high frequency part of the required band, and changes the peaking characteristic with respect to the input signal by the control signal V _C of the comparison control circuit 3.

Therefore, even if the characteristics of the transmission line, the receiving section, etc. are arbitrarily changed, a desired margin can always be obtained in the eye opening of the output signal, and similarly to the above, the identification section in the subsequent stage is less likely to make an identification error. . Preferably, in the present invention (2),
The first amplitude detection circuit 1 is composed of a peak detection circuit 11 that detects the peak level of the input signal, and the second amplitude detection circuit 2 is a peaking circuit 2 that emphasizes the high-speed signal component of the input.
1 and a peak detection circuit 22 for detecting the peak level of its output signal.

Now, the input signal waveform a has the bit "11110".
If the pattern is “101”, waveform interference (amplitude deterioration) is mainly caused by the bit “101” due to insufficient bandwidth.
This is a part of the high speed signal component of "0". Therefore, the peak detection circuit 11 in this case substantially detects the peak level V _P1 of the input low-speed signal component. On the other hand, when the input signal a is sufficiently peaked by the peaking circuit 21 which emphasizes the high speed signal component, the output signal b becomes as shown in the figure. Therefore, the peak detection circuit 22 in this case detects the peak level V _P2 of the peaked high-speed signal component. However, since the peaking contribution of the peaking circuit 21 is known (constant), the peak detection output V _P2 of the peak detection circuit 22 eventually reflects the amplitude V _P2 'of the high-speed signal component of the input signal a before peaking. Can be Therefore, a simple peak detection circuit 1
With the configuration employing 1 and 22, the eye opening of the output signal can be adaptively controlled as desired.

In the waveform shaping circuit of the present invention ( 3 ) in FIG. 3, the first peak detection circuit 11 detects the peak level of the input signal a. The variable gain frequency characteristic circuit 4 has a peaking characteristic of gain in the high frequency part of the required band, and
A peaking characteristic for the input signal a is variably controlled by a control signal V _C described later. Second peak detection circuit 22
Detects the peak level of the output signal b of the variable gain frequency characteristic circuit 4. The comparison control circuit 3 then outputs the level detection outputs V _P1 and V _P of the first and second peak detection circuits 11 and 22, respectively.
_P2 is compared, and the control signal V _C is generated so that the ratio V _P2 / V _P1 becomes a predetermined value exceeding 1.

According to the present invention ( 3 ), since the variable gain frequency characteristic circuit 4 also has the function of the peaking circuit 21 of FIG. 2, the peaking circuit 21 can be omitted and the overall circuit configuration becomes simple. Further, since the second peak detection circuit 22 directly detects the peak level V _P2 of the output signal b after peaking, the comparison control circuit 3 has the peak detection level V _P2.
P2 can be directly used for control judgment.

Further, preferably, the gain frequency characteristic variable circuit 4 of FIGS. 2 and 3 is constituted by a peaking variable circuit 41 capable of varying the gain in the high band portion of the required band. In the waveform shaping circuit of the present invention ( 5 ) in FIG. 4, the first peak detection circuit 11 detects the peak level of the input signal a. The peaking circuit 21 preferably sufficiently peaks the gain of a predetermined high frequency part of the input signal a in the required band. The second peak detection circuit 22 detects the peak level of the output signal b of the peaking circuit 21. The comparison control circuit 3 includes the first and second
Peak detection outputs V _P1 of the peak detection circuits 11 and 22 of
V _P2 is compared, and a control signal V _C is generated so that the ratio V _P2 / V _P1 becomes a predetermined value exceeding 1. Then, the frequency band variable circuit 5 capable of varying the frequency cutoff characteristic in the high frequency band controls the gain of the output signal b of the peaking circuit 21 by the control signal V _C of the comparison control circuit 3 to limit the frequency band. Therefore, the eye opening of the output signal can be adaptively controlled with a simple configuration.

[0018]

Embodiments of the present invention will be described in detail below with reference to the accompanying drawings. The same reference numerals denote the same or corresponding parts throughout the drawings. FIG. 2 is a circuit diagram of the waveform shaping circuit of the first embodiment, in which 1 is an amplitude detection circuit for detecting the amplitude of an input low speed signal component, 2 is an amplitude detection circuit for detecting the amplitude of an input high speed signal component, Reference numeral 3 is a comparison control circuit, and 4 is a gain frequency characteristic variable circuit.

The gain frequency characteristic variable circuit 4 of one example comprises a peaking variable circuit 41 capable of peaking control of the gain in the high frequency part of the required band by the control signal V _C.
FIG. 5 shows a circuit diagram of the peaking variable circuit of the embodiment. This circuit has a differential amplification circuit type suitable for being integrated into an IC, and basically, the emitters of the transistors Q ₁ and Q ₂ (that is, the negative feedback resistor R It is an emitter peaking variable circuit of a type in which a variable capacitance C _be is inserted in parallel with ( _E ).

Further, the transistor Q₁, Q₂Each collect
The base of the transistor Q is a transistor Q ₃, Q_FourEach of them
Code connected, thus transistor Q₁, Q₂
The impedance seen from the collector to the load side is sufficient
small. Therefore, the transistor Q₁, Q₂The base of
Each junction capacitance C existing between collectors_bcDue to the mirror
The effect of the capacitance is also greatly reduced, so this emitter grounding
The amplifier circuit has a sufficient wide band characteristic.

On the other hand, each variable capacitance C _be is a diffusion capacitance existing between the base and the emitter of each of the transistors Q ₅ and Q ₆ , and the capacitance value C _be has an emitter operating current I _EQ of each of the transistors Q ₅ and Q _6. Increases in proportion to. In the grounded-emitter amplification operation of the transistors Q ₁ and Q ₂ , there is a relation of R _E << 1 / jωC _be in the intermediate frequency region of the required band, and the normalized gain of the amplification circuit at that time is set to 0 dB, for example. In the high band of the required band, R _E > 1 / jωC _be , and the gain of the amplifier circuit is peaked to the + side. The strength of peaking is proportional to the capacitance value C _be, and the capacitance value C _be
Can be variably controlled by applying a control voltage V _C to the variable current type constant current source VI.

[0022] In such a configuration, the transistors Q _1, Q ₂ of the input signal V _in level balanced to each base, V _in / are respectively input from the collectors of the transistors Q _3, Q ₄ levels balanced is The output signals V _out / and V _out are taken out respectively. FIG. 6 shows a circuit diagram of a peaking variable circuit according to another embodiment. This circuit is basically a collector / peaking variable circuit of a type in which a variable inductive component is connected in series to each load resistance R _L of the transistors Q ₁ and Q ₂ which form a broadband emitter grounded amplifier circuit.

[0023] That is, the diode D ₁ to the base circuit (i.e., the resistance component R) when the impedance of the transistor circuit Q ₃ inserted viewed from the emitter of the Q _3, transition frequencies of h _fe = 1 of the transistor Q ₃ f _T
It is known that an inductive component having a size of R / 2πf _T defined by the relationship with is visible. Therefore, due to this inductive component, peaking characteristics can be obtained in the high range of the grounded-emitter amplifier circuit.

In this case, the resistance value R of the diode D ₁ is variable depending on the current flowing therethrough, so that if the current of the variable current type constant current source VI ₁ is controlled by the control voltage V _C , the strength of peaking is controlled. it can. The same applies to the circuit of the transistor Q ₄ . By the way, if the control voltage V _C is fixed (constant) in each of the peaking variable circuits of FIGS. 5 and 6, the peaking circuit 21 of FIG. 2 is obtained.

Further, this peaking circuit may be used in the gain frequency characteristic circuit section 10 of FIG. 8 and 9 show operations (1) and (2) of the waveform shaping circuit of the embodiment. Figure 8
FIG. 8A shows a case where the peaking characteristic is set relatively low (weak), and the corresponding eye pattern of the output signal of FIG. 8B shows a slight (appropriate) input high-speed signal component. Large amounts of overshoot and undershoot have been obtained.

FIG. 9A shows a case where the peaking characteristic is set relatively high (strongly), and the eye pattern of the output signal of FIG. 9B corresponding to this shows that the high-speed signal component of the input. Excessive overshoot and undershoot are seen. Of course, the amplitude of the high-speed signal component of the input may be significantly deteriorated, so the overshoot and undershoot in this case are not excessive but appropriate.

Therefore, in the configuration of FIG. 1, the peaking characteristic is appropriately set within the range of FIG. 8A to FIG. An eye pattern is obtained. On the other hand, when there is a change in the characteristics of the transmission line, the peaking variable circuit 41 has the configuration shown in FIG.
Adaptively controls the peaking characteristics of.

That is, in FIG. 2, the peak detection circuit 11
Detects the peak level of the low-speed signal component of the input. Although not shown, the peak detection circuit 11 can be configured by a known circuit including a diode and a capacitor. A configuration in which a capacitor is connected to the emitter of a transistor is often used on the IC chip. Now, assuming that the input signal waveform a is a pattern of bit "11110101", waveform interference (amplitude deterioration) due to insufficient bandwidth or the like is mainly in the high speed signal pattern portion of bit "1010". Therefore, the peak detection circuit 11 in this case substantially detects the peak level V _P1 of the input low-speed signal component.

On the other hand, the peak level V _P2 'of the input high speed signal component cannot be detected as it is due to the influence of the low speed signal component. Therefore, the peaking circuit 21 temporarily emphasizes the high-speed signal component of the input signal a to obtain its output signal b. In this way, the peak level V _P2 of the high speed signal component can be effectively detected by the peak detection circuit 22 which is the same as the peak detection circuit 11. Moreover, the peaking circuit 2
Since the peaking amplification factor by 1 is known, the peak detection circuit 22 or the comparison control circuit 3 detects the detected peak level V
The peak level V _P2 'of the high-speed signal component before peaking can be generated based on _P2 .

Then, the comparison control circuit 3 outputs the peak detection outputs V _P1 and V _P2 (= V _P2 ') of the peak detection circuits 11 and 22.
And the control signal V _C is generated so that the ratio V _P2 / V _P1 becomes a predetermined value exceeding 1. Such comparison control circuit 3, although not shown, for example, V a differential amplifier for detecting the difference between _P1 and V _P2, the difference by comparing the output with a predetermined threshold value of the differential amplifier ( It is composed of an operational amplifier that generates a control signal V _C so that the ratio V _P2 / V _P1 ) becomes constant, and a level shift circuit for converting the signal level if necessary. Thus, the output signal of the peaking variable circuit 41 can always obtain a desired eye pattern.

FIG. 3 is a circuit diagram of the waveform shaping circuit of the second embodiment. In the second embodiment, the peak detection circuit 22 is configured to detect the peak level V _P2 of the output signal b after peaking. Therefore, the peaking circuit 21 of FIG. 2 can be deleted, and the circuit becomes simple. Further, the comparison control circuit 3 can use the detected peak level V _P2 of the peak detection circuit 22 as it is for the control calculation.

FIG. 4 is a circuit diagram of the waveform shaping circuit of the third embodiment. In the third embodiment, a fixed peaking circuit 21 is provided instead of the peaking variable circuit 41 shown in FIG. Therefore, the input signal a is unconditionally peaked to a predetermined characteristic (preferably an excessive characteristic), and the intermediate signal b
Becomes Further, the intermediate signal b is used in the frequency band variable circuit 5
Is input to, where the frequency band is limited. This frequency band limitation is performed according to the control voltage V _C of the comparison control circuit 3 so that the ratio V _P2 / V _{P1 of} V _P1 and V _P2 becomes a predetermined value exceeding 1.

FIG. 7 shows a circuit diagram of the frequency band variable circuit of the embodiment. This circuit basically has a variable capacitance C _{be in} the collectors (that is, in parallel with the load impedance) of the transistors Q ₁ and Q ₂ which form the broadband grounded-emitter amplifier circuit.
It is a variable frequency band circuit of the type that inserts. Similarly to the above, cascode-connected transistors Q ₃ and Q
Due to the presence of ₄ , this amplifier circuit has a wide band. Further, if the capacitance value C _be is changed by the control voltage V _C , the cutoff frequency in the high frequency band can be controlled.

Although the peak detecting circuits 11 and 22 having a simple structure are used as the amplitude detecting circuit in the above embodiment, the present invention is not limited to this. For example, the input signal may be separated into a high-speed signal component and a low-speed signal component by a bandpass filter, and the respective amplitudes may be detected. Further, since the peaking circuit 21 of FIG. 2 has nothing to do with the main signal line, it does not need to have a wide band by itself. Therefore, for example, a differentiating circuit that emphasizes only the high-speed signal component of the input may be used.

The gain frequency characteristic varying circuit 4 can be realized by various configurations other than the peaking varying circuit 41 of the embodiment. For example, a high-order active filter circuit having gain and peaking characteristics may be used. Although the peak value at the bit 1 level is detected in the above embodiment, the peak value at the bit 0 level or the peak value of the difference (distance) between bits 1 and 0 may be detected. Furthermore, the transmission signal is a unipolar signal system,
It does not matter whether the bipolar signal system is used.

Further, in the above-mentioned embodiment, the case of the baseband signal communication by the optical or electric signal is described, but the present invention is not limited to this. It is obvious that the waveform shaping circuit of the present invention can also be applied to waveform shaping of a demodulated baseband signal obtained by detecting / demodulating an RF wave. Although a plurality of preferred embodiments of the present invention have been described above, it goes without saying that various changes in configuration and control can be made without departing from the spirit of the present invention.

[0037]

As described above, since the waveform shaping circuit of the present invention has the above-mentioned structure, a good eye opening can always be obtained in the received waveform.

[Brief description of drawings]

FIG. 1 is a diagram illustrating the principle of the present invention.

FIG. 2 is a circuit diagram of a waveform shaping circuit according to a first embodiment.

FIG. 3 is a circuit diagram of a waveform shaping circuit according to a second embodiment.

FIG. 4 is a circuit diagram of a waveform shaping circuit according to a third embodiment.

FIG. 5 is a circuit diagram of a peaking variable circuit according to an embodiment.

FIG. 6 is a circuit diagram of a peaking variable circuit according to another embodiment.

FIG. 7 is a circuit diagram of a frequency band variable circuit according to an embodiment.

FIG. 8 is a diagram (1) for explaining the operation of the waveform shaping circuit according to the embodiment.

FIG. 9 is a diagram (2) explaining the operation of the waveform shaping circuit according to the embodiment.

FIG. 10 is a diagram (1) illustrating a conventional technique.

FIG. 11 is a diagram (2) illustrating a conventional technique.

[Explanation of symbols]

1, 2 amplitude detection circuit 3 Comparison control circuit 4 Gain frequency characteristic variable circuit 5 Frequency band variable circuit 10 Gain frequency characteristic circuit

Front page continuation (72) Inventor Hiroshi Miyamoto 1-6, Uchisaiwaicho, Chiyoda-ku, Tokyo Inside Nippon Telegraph and Telephone Corporation (56) Reference JP-A-7-7345 (JP, A) JP-A-7-193546 (JP, A) JP-A-7-15476 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) H04L 25/03 H04B 10/00

Claims (5)

(57) [Claims] 1. A waveform shaping circuit for shaping a signal waveform of a pulse signal train, comprising: a first amplitude detection circuit for detecting an amplitude of an input low speed signal component; and a second amplitude detection circuit for detecting an amplitude of an input high speed signal component. Comparison for comparing the detection outputs V _P1 and V _P2 of the amplitude detection circuit and the first and second amplitude detection circuits and generating a control signal such that the ratio V _P2 / V _P1 becomes a predetermined value exceeding 1. A waveform characterized by comprising a control circuit and a gain-frequency characteristic variable circuit having a gain peaking characteristic in a high-frequency part of a required band and having a peaking characteristic variable with respect to an input signal by a control signal of the comparison control circuit. Shaping circuit. 2. A first amplitude detection circuit is composed of a peak detection circuit for detecting a peak level of an input signal, and a second amplitude detection circuit is a peaking circuit for emphasizing an input high-speed signal component and its output signal. waveform shaping circuit according to claim 1, characterized in that is constituted by a peak detection circuit for detecting a peak level of. 3. A waveform shaping circuit for shaping a signal waveform of a pulse signal train, comprising: a first peak detection circuit for detecting a peak level of an input signal; and a peaking characteristic of gain in a high frequency part of a required band, A gain frequency characteristic variable circuit in which a peaking characteristic with respect to an input signal is made variable by a control signal, a second peak detection circuit for detecting a peak level of an output signal of the gain frequency characteristic variable circuit, and first and second peak detection And a comparison control circuit for comparing the respective detection outputs V _P1 and V _P2 of the circuit and generating the control signal such that the ratio V _P2 / V _P1 becomes a predetermined value exceeding 1. circuit. 4. A any one of claims 1 to 3 gains the gain frequency characteristic variable circuit in the high frequency band of the required bandwidth, characterized by being configured by a variable peaking variable circuit serial
Waveform shaping circuit of the mounting. 5. A waveform shaping circuit for shaping a signal waveform of a pulse signal train, comprising: a first peak detection circuit for detecting a peak level of an input signal; and an input signal as an input, with a gain in a high frequency part of a required band. A peaking circuit having a peaking characteristic, a second peak detection circuit for detecting the peak level of the output signal of the peaking circuit, and the respective detection outputs V _P1 and V _P2 of the first and second peak detection circuits are compared, A comparison control circuit that generates a control signal such that the ratio V _P2 / V _P1 becomes a predetermined value exceeding 1, and a frequency cutoff characteristic of the gain in the high frequency part of the required band, and peaking by the control signal of the comparison control circuit. A waveform shaping circuit, comprising: a frequency band variable circuit that performs frequency band limitation control of a gain for an output signal of the circuit.