JPS6366451B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to an equalization amplifier circuit that uses a switched capacitor filter to compensate for line loss and to perform waveform shaping. <Prior Art> Line loss in signal transmission is generally proportional to the square root of the frequency f, as shown in FIG. 1, and the longer the length of the line, the greater the loss at the same frequency. In FIG. 1, the parameters indicate the length of the line, l ₁ >l ₂ >l ₃ . This kind of line loss is processed by a switch capacitor filter (hereinafter referred to as SCF).
In order to perform equalization using , a configuration as shown in FIG. 2 was generally adopted. SCF1 for line loss compensation
00, a waveform shaping SCF 200 is connected in cascade between a signal input terminal 1 and an equalized waveform output terminal 2. In the SCF 100 for line loss compensation, input terminal 1 is connected to the inverting input side of operational amplifier A ₁ through capacitive element 6, and capacitive element 5 is connected to input terminal ₁ and the inverting input of operational amplifier A ₁ by analog switches S 1 and S ₂ . Both ends of the capacitive element 5 can be switched and connected to the ground side by switches S ₁ and S ₂ . A capacitive element 4 is connected between the inverting input side and the output side of the operational amplifier _A1 , and a capacitive element 7 is connected between them by analog switches _S3 and _S4 , and the switches _S3 and _S4 are switched. Thus, both ends of the capacitive element 7 can be grounded.
The non-inverting input side of the operational amplifier _A1 is grounded, and the output side is connected to the output terminal 3. SCF2 for waveform shaping
00, the output terminal 3 of the SCF 100 for line loss compensation is connected to the inverting input side of the operational amplifier _A2 through the capacitive element 10, and one end of the capacitive element 9 is connected to the terminal 3 and the inverting input side of the operational amplifier _A2 by the analog switch _S5. The other end is grounded. A capacitive element 8 is connected between the inverting input side and the output side of the operational amplifier _A2 , and both ends of the capacitive element 11 are connected between these by analog switches _S6 and _S7 or grounded. The non-inverting input side of the operational amplifier _A2 is grounded, and the output side is connected to the output terminal 2. Although FIG. 2 shows an example realized with a first-order SCF, it is also possible to realize it with a second-order or higher-order SCF. The sampled and held waveform input from terminal 1 in Fig. 2 is integrated by the line loss compensation SCF 100 by switching the analog switches S ₁ to _{S 4} alternately to the φ side and to the φ side in synchronization with the sampling clock. , is output to terminal 3. Input voltage of terminal 1
V _i , the output voltage of terminal 3 is V ₃ , the capacitance values of capacitive elements 4 to 7 are C ₄ to _{C 7} , and the sampling clock frequency is f _s , the transfer function of the SCF 100 for line loss compensation is as follows: become. V ₃ /V _i =-(C ₅ /C ₄ +C ₆ /C ₄ )-C ₆ /C ₄ Z ^-1 /(1+C
₇ /C ₄ )−Z ⁻¹ Z=exp(j2πf/f _s ) (1) Any pole, zero point, or maximum gain can be obtained by changing the capacitance values C ₅ to C ₇ . Capacity value
C ₅ to C ₇ prepare various capacities 5 to 7, respectively.
By switching and using these capacitive elements with a switch, it becomes possible to equalize various line losses as shown in FIG. The waveform shaping SCF 200 is configured as a low-pass filter, and the voltage at terminal 3 is integrated by the waveform shaping SCF 100 by switching switches S ₅ to S ₇ alternately to the φ side and φ side in synchronization with the sampling clock. , is output to terminal 2. Voltage at terminal 3 V ₃
The transfer function between the output V ₀ of terminal 2 and the capacitive element 8
.about.11 are _C8 to _C11 , and the frequency of the sampling clock is _fs , it is expressed by the following equation. V ₀ /V ₃ = −C ₁₀ /C ₈ + (C ₉ /C ₈ −C ₁₀ /C ₈ )Z ^-1 /(
1+C ₁₁ /C ₈ )−Z ^-1 Z=exp(j2πf/f _s ) (2) By selecting the capacitance values C ₉ to _{C 11} , the cutoff frequency of the low-pass filter can be changed. , you can select the cutting frequency according to the transmission speed. In order to equalize the maximum G decibel line loss for m types of transmission speeds, conventionally the capacitive elements 5 to 7 in Fig. 2 are connected in the form shown in Fig. 3.
Further, the capacitive elements 9 to 11 in FIG. 2 were realized in the form shown in FIG. 4, and the line loss characteristics of each were equalized. Considering that the maximum loss G decibel is equalized in ΔG decibel steps, the number n of frequency characteristics to be equalized for each transmission rate is expressed by the following equation. n=G/△G (3) In Figure 3, n for the first transmission speed
In order to obtain the normal line equalization characteristics, C ₁₁
This is realized by preparing a capacitive element group consisting of n capacitive elements of ~ _C1o , and switching these capacitive elements with analog switches _S11 ~ _S1o provided in pairs at both ends thereof. Further, in order to apply the present invention to m types of transmission speeds, it is sufficient to prepare m sets of the capacitive element groups. At this time, the capacitance C _T between terminals 21 and 22 is C _T = _n 〓 ^q1 _o 〓 ^r=1 k _qr C _qr (4) where k _qr is the paired analog switch S _qr
It is 1 when it is in a conductive state, and it is 0 when it is in a non-conductive state. Regarding the waveform shaping SCF 200, the cutting frequency of the low-pass filter may be changed for each transmission speed. Therefore, in Fig. 4, m capacitive elements C ₁
This is achieved by preparing C _n in advance and changing the shearing frequency by switching it with analog switches SW ₁ to SW _n provided in pairs at both ends of the capacitive element according to the transmission speed. Figures 3 and 4
Line loss compensation SCF when using the method shown in the figure
100, the waveform shaping filter 200, and the overall frequency characteristics from the input terminal 1 to the equalized waveform output terminal 2 in FIG. 2 are shown in FIG. Figure 5 shows the frequency characteristics when it is applicable to two types of transmission speeds, and the characteristics of the first transmission speed are shown as solid lines.
The characteristics of the second transmission speed are shown by dotted lines, where A is SCF100 for line loss compensation and B is SCF20 for waveform shaping.
0 and C are overall frequency characteristics. The total number of capacitive elements N _T to equalize the losses of n different line lengths for m different transmission speeds using the method shown in Figures 3 and 4 is N _T = α・m・n+βm (4) Where, α is the number of capacitive elements other than the integral capacitive element of SCF100 for line loss compensation, and β is for waveform shaping.
This is the number of capacitive elements other than the integral capacitive element of the SCF 200. As is clear from Equation (4), in the conventional circuits shown in Figures 3 and 4, as the number of meters of applied transmission speed increases, the number of capacitive elements must be increased in proportion to the number of meters, so it is necessary to convert this into an LSI. In some cases, there was a disadvantage that the area occupied by the chip increased. Also the third
As shown in Figure 4, since the same number of analog switches as the number of capacitive elements are added, the stray capacitance increases, deteriorating the characteristics, and making highly accurate equalization difficult. Ta. <Objective of the Invention> The present invention eliminates these drawbacks and provides an equalization amplifier circuit which is highly accurate and occupies a small chip area when implemented in LSI. <Embodiment> FIG. 6 shows an embodiment of the present invention, in which the line loss compensation SCF 100 and the waveform shaping SCF 200 are connected between the signal input terminal 1 and the equalized waveform output terminal 2, as in the case of FIG. 2. connected in cascade. Capacitive elements C ₅₁ to _{C 5o} are selectively connected as capacitive element 5 by an analog switch, and similarly capacitive elements 6, 7, 9, 10,
Each capacitive element 11 is selectively connected by an analog switch. SCF100 for line compensation, SCF200 for waveform shaping
The transfer functions are expressed by the above equations (1) and (2), respectively, where the capacitance values of the capacitive element groups 5-7 and 9-11 are Ci (i=5-7, 9-11). Also, at this time, Ci is expressed by the following formula. C _i = 〓 ^q k _iq C _iq (i=5~7, 9~11) (5) In this example, the capacitance value C _iq (i=5 ~
7. q=1 to n, k, l,...) are determined as shown below. In the following explanation, for m types of transmission speeds, the maximum loss to be equalized is G decibels,
Although the equalization step is assumed to be ΔG decibels, it can be similarly applied to the case where the maximum loss to be equalized and the equalization step change depending on the transmission speed. Further, the transmission speed to be equalized up to the highest frequency range is called the first transmission speed, and the transmission speed to be equalized up to the mth high frequency range is called the m-th transmission speed. (1) First, n capacitive elements (n=G/ΔG) are prepared in order to equalize the first transmission rate in ΔG steps. (2) Next, capacitive elements for the capacitive elements 5 to 7 are prepared for the portion where the frequency characteristic of the second transmission rate cannot be equalized with the frequency characteristic of the first transmission rate. The maximum frequency to be equalized at the second transmission rate is
1/P ₂ of the maximum frequency to be equalized at the transmission speed of
Assuming that, the line loss is generally proportional to the square root of the frequency, so the frequency characteristic that equalizes the first transmission speed can equalize up to 1/√ ₂ of the maximum line loss G at the second transmission speed. . Therefore, the unequalized loss range G/√ ₂ at the second transmission rate
A capacitive element for equalizing up to G is prepared. Assuming that the number of new capacitive elements to be prepared is _N2 , it is expressed by the following equation. (3) Similarly, for the 3rd to mth transmission speeds, the unequaled portions of the frequency characteristics up to the (q-1)th (q = 3 to m) are equalized in steps of △G decibels or less. Prepare a capacitive element so that it can be used. As for the SCF200 for waveform shaping, it is only necessary to change the cutting frequency of the low-pass filter for each transmission speed, so as shown in Figure 6, capacitive element groups 9 to 1 are used.
m capacitive elements C _ir (i=9~
11, r=1~m) is prepared, and the capacitive element C _ir
Analog switches provided in pairs at both ends of
By switching S _ir (i=9 to 11, r=1 to m), m types of cutting frequencies are obtained. SCF for line loss compensation when using this example
(Fig. 6 100), SCF for waveform shaping (Fig. 6 200)
and equalized waveform output terminal 2 from input terminal 1 in FIG.
The overall frequency characteristics up to this point are shown in Fig. 7. FIG. 7 shows an example in which the system can be applied to two types of transmission speeds, where A is the SCF for line loss compensation, B is the SCF for waveform shaping, and C is the overall frequency characteristic. The maximum frequency to be equalized at the q-th transmission rate is 1/ of the maximum frequency to be equalized at the first transmission rate.
Pr, and the numbers of capacitive elements other than the integral capacitive elements of the SCF 100 for line loss compensation and the SCF 200 for waveform shaping are respectively α and β, then for m types of transmission speeds, the line The total number N _T of capacitive elements other than the integral capacitive element for equalizing loss is expressed by the following equation. <Effects> In this embodiment, the number of capacitive elements required for the SCF 100 for line loss compensation does not need to increase in proportion to the number of meters of transmission speed to which it is applied, so the number of capacitive elements is smaller than that of the conventional method. It can function as an equalizing amplifier for multiple transmission rates with a small number of analog switches. As an example, Table 1 shows the number of sets of capacitive elements and analog switches required when applicable to two and three types of transmission speeds.

[Table] Here, the maximum frequency to be equalized at the second transmission rate is 1/2 of the first transmission rate, and the maximum frequency to be equalized at the third transmission rate is 1/3 of the third transmission rate. , the parameters in equations (4) and (6) are G=40dB,
ΔG=2 dB, n=20, α=3, and β=3. In the case of the example in Table 1, it is possible to reduce the number of capacitive elements by about 20 to 40% by using this embodiment, and similarly when the parameters Pr, G, △G, α, β are different, According to this embodiment, the number of capacitive elements and analog switches can be reduced. As explained above, according to the present invention, it is possible to construct an SCF equalization amplifier circuit that can be applied to multiple transmission speeds with a smaller number of capacitive elements and fewer analog switches than in the past, and when integrated, the occupied area is reduced. This has the advantage of being able to reduce Furthermore, since the number of analog switch wirings can be reduced in the present invention, there is an advantage that accuracy deterioration due to stray capacitance is small and highly accurate equalization can be performed.

[Brief explanation of drawings]

Figure 1 is a frequency characteristic curve diagram of line loss, Figure 2 is a circuit diagram showing a general configuration example of an equalization amplifier circuit using SCF, and Figures 3 and 4 are for multiple transmission speeds. FIG. 5 is a diagram showing an example of frequency characteristics when the configurations of FIGS. 3 and 4 are used, and FIG. 7 is a circuit diagram showing an embodiment of the present invention, and FIG. 7 is a diagram showing an example of frequency characteristics of the circuit of FIG. 6. 100: SCF for line loss compensation, 200: SCF for waveform shaping, 1: Signal input terminal, 2: Equalized waveform output terminal, 3: SCF output terminal for line loss compensation, 4 to 1
1: Capacitive element, A ₁ , A ₂ : Operational amplifier, S ₁ to _{S 7} :
Analog switch, C _ij (i=5~7, 9~11, j
=1~n): Capacity, S _ij (i=5~7, 9~11, j
=1~n): Analog switch.

Claims (1)

[Claims] 1 An AGC equalizer for PCM signals that adaptively compensates for the line loss and distortion of the signal transmission line is
In order to compensate for the f loss characteristic (loss at frequency f is proportional to √), we have multiple discrete gain characteristics that approximate the √ characteristic, and these characteristics are combined with a switch capacitor consisting of a semiconductor switch, a capacitor, and an operational amplifier. A loss equalizer consists of a circuit and realizes the plurality of discrete characteristics by switching the capacitors used, and a waveform shaping device consists of a switch capacitor circuit and removes high frequency components that interfere with equalization. In order to be able to apply the equalization amplifier circuit to multiple transmission systems, which is realized by both the low-pass filter and the low-pass filter, the system with the highest transmission speed among the multiple transmission systems to be equalized is Frequency range 0~ _f1
(Hz), the first capacitor group for equalizing the equalization loss range 0 to G (dB) with a constant gain step △G (dB) at frequency f ₁ , and the second highest transmission rate. The loss range that cannot be equalized by the first capacitor group for the frequency range 0 to f ₂ (Hz) of the system, that is, the loss G/√ ₁ to G (dB) at frequency f ₂
a second group of capacitors that equalizes with a constant gain step △G (dB) at frequency f ₂ and the following frequency range 0 to f _i (Hz) of the system with the i-th highest transmission rate.
The loss range that cannot be equalized in the i-1st capacitor group, that is, the loss G/√ _i-1 at frequency f _i
~G (dB) at a constant gain step △ at frequency f _i
A loss equalizer consisting of an i-th capacitor group that equalizes by G (dB), and a cut-off frequency of f ₁ ′,
f ₂ ′...f _i ′ (Hz) (f _k ′ is the cutoff frequency for the system with the kth highest transmission rate) for waveform shaping with i types of capacitor groups so that it can be switched in i ways Equalization amplifier circuit consisting of a low-pass filter.