JPH07240664A - Analog filter - Google Patents

Abstract

(57) [Abstract] [Object] With regard to an analog filter, it is an object of the present invention to provide an analog filter having high versatility and capable of supporting various forms of analog signal processing. [Structure] The phase of the output voltage Vout of the second voltage / current conversion rate variable integrating means is inverted and added to the input voltage Vin,
A first voltage gain varying means 200 for amplifying and outputting with a variable voltage gain, and an output voltage of the first voltage gain varying means with a variable voltage / current conversion rate after being converted into a current,
The first voltage / current conversion rate is inverted by inverting the phases of the first voltage / current conversion rate variable integration means 300 for integration and output and the output voltage Vout of the second voltage / current conversion rate variable integration means. Second voltage gain varying means 600 for adding with the output of the variable integrating means and amplifying with a variable voltage gain to output.
And a second voltage / current conversion rate variable type integration means 700 for converting the output voltage of the second voltage gain variable means into a current with a variable voltage / current conversion rate, and integrating and outputting the current. .

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an analog filter which is essential for signal processing such as waveform equalization. In both the fields of communication and information equipment, the speed of signals to be processed has been increasing, and there are still some areas where digital processing is not sufficient. Therefore, it is no exaggeration to say that how well signal processing can be performed in analog is the decisive factor in device performance. The present invention provides a highly versatile analog filter that can handle various forms of analog signal processing.

[0002]

2. Description of the Related Art Conventional analog filters are either passive filters using discrete components or CMOS.
Switched-capacitor (SC) filters, which apply technology, were the mainstream. The former is suitable for speeding up, but since it has a coil and the like, it requires a mounting space, is expensive, and is almost impossible for variable adjustment. The latter can be integrated into an IC and is widely used, but generally has a low processing speed,
Also, because a high-speed sampling clock is required,
(To prevent noise) Consideration should be given to the separation technology from other analog circuits.

Further, as shown in FIG. 12, there is a BIQUAD circuit which is composed of an integrator 17 having a loss, an anti-phase integrator 18, and an anti-phase amplifier 19 and realizes a biquadratic transfer function. In particular BIQUA using voltage / current conversion means
The D circuit is BIQUAD using a switched capacitor.
It is much faster than circuits and is widely used in the field of magnetic recording, but it is only for specific applications.

[0004]

As described above, the conventional analog filter using the BIQUAD circuit is only for a specific purpose.

Therefore, an object of the present invention is to provide a versatile analog filter which can deal with various forms of analog signal processing.

[0006]

The above problems can be solved by the circuit configuration shown in FIG. That is, in FIG. 1, (claim 1) is an analog filter using a BIQUAD circuit, wherein the BIQUAD circuit is fed back from a voltage fed back from an output of a second voltage / current conversion factor variable type integrating means described later. The first voltage gain varying means 200 which inverts the phase of Vout, adds it to the input voltage Vin, amplifies the added value with a variable voltage gain, and outputs it.
A first voltage / current conversion rate variable integrating means 300 for converting the output voltage of the first voltage gain variable means into a current with a variable voltage / current conversion rate, and integrating and outputting the current; The phase of the voltage Vout fed back from the output of the second voltage / current conversion rate variable integrating means is inverted and added to the output of the first voltage / current conversion rate variable integrating means, and the added value can be changed. The second voltage gain variable means 600 for amplifying and outputting by the voltage gain, and the second voltage gain varying means for converting the output voltage of the second voltage gain variable means into a current by the variable voltage / current conversion rate, and then integrating and outputting. The second voltage / current conversion rate variable type integration means 700.

(Claim 2) The first voltage / current conversion rate variable type integrating means and the second voltage / current conversion rate variable type integrating means are replaced by integrating means each comprising a capacitor, a resistor and an operational amplifier. It has a different configuration.

(Claim 3) In the analog filter according to claim 1, the input voltage to the first voltage gain varying means is branched and input, and amplified by a variable voltage gain K to obtain a positive and negative voltage. A third voltage gain varying means 400 for outputting a signal and a switch means 500 for selectively outputting one of the outputs of the third voltage gain varying means according to a switching signal from the outside are provided, and are selected by the switch means. Further, the output of the third voltage gain varying means is added to the output of the second voltage / current conversion rate varying integrating means.

(Claim 4) The BI according to claim 1
Two analog filters each composed of a QUAD circuit, the third voltage gain varying means according to the third aspect, and a switch means are arranged in parallel for differential operation.

[0010]

In FIG. 1, the input voltage to the first voltage gain varying means is Vin, the gains of the first, second and third voltage gain varying means are G ₁ , G ₂ , K, 1st and 3rd, respectively. The conversion rates of the second voltage / current conversion rate variable type integrating means are respectively set to gm.
₁ , gm ₂ , C is the capacity for integration of the first and second variable voltage / current conversion rate variable integration means, and Vout is the output voltage of the second voltage / current conversion rate variable integration means. The output of the voltage-to-current conversion rate variable integrating means of

[0011]

[Equation 1]

[0012] When summarized by Vin and Vout respectively,

[0013]

[Equation 2]

[0014] Therefore, the transfer function T (S) is

[0015]

[Equation 3]

Is required. Here, S = jω, ω = 2
πf and f are frequencies. When K of the numerator polynomial in the above equation is +, it is a band stop type, when it is −, it is a high-frequency emphasis type, and when K = 0, it is a low-pass type, and each is determined by the switching state of the switch means. As a result, various forms of analog signal processing can be accommodated.

Further, the voltage / current conversion rate and the voltage gain are arbitrarily changed by using the first and second voltage / current conversion rate variable type integration means and the first, second and third voltage gain variable means. As a result, the transfer function of the filter can be freely created, and a wider adjustment range than before can be secured.

[0018]

2 is a block diagram of a BIQUAD circuit according to an embodiment of the present invention. In the figure, 2-1, 2-2, 4-1, 4-2
, 6-1 and 6-2 are voltage amplifiers, 3-1, 3-2, 7-1 and 7-2 are voltage / current converters, 1 and 8 are buffers, 5-1 and 5-2 are switches. Yes, one BIQUAD circuit 9 is composed of a circuit composed of the voltage amplifiers 2-1, 6-1 and the voltage / current converters 3-1, 7-1 and the capacitor C, and the voltage amplifiers 2-2, 6- 2
Another BIQUAD circuit 10 is composed of a circuit composed of the voltage / current converters 3-2 and 7-2 and the capacitor C. The two BIQUAD circuits 9 and 10 are operated differentially.

First, the transfer function of the BIQUAD circuit is obtained. The + input voltage of the voltage amplifier 2-1 is Vin, the output voltage of the voltage / current converter 7-1 is Vout, the gain of the voltage amplifier 2-1 is G _a , and the conductance of the voltage / current converter 3-1 is g.
m _a , the gain of the voltage amplifier 6-1 is G _b , the voltage / current converter
The conductance of the 7-1 and the gm _b,

[0020]

[Equation 4]

[0021] Summing up with Vin and Vout respectively,

[0022]

[Equation 5]

Therefore, the transfer function T (S) is calculated from the equation (2).

[0024]

[Equation 6]

Is required. Where S = jω,
ω = 2πf, f is the frequency. From the equation (3), the parameters ω _o (resonance angular frequency) and Q (selectivity) of the active filter are respectively given by the following equations.

[0026]

[Equation 7]

In equation (3), when the sign of K in the numerator polynomial is +, it is a band stop type, when it is −, it is a high-frequency emphasis type, and K =
When it is 0, it becomes a low pass type, and switches 5-1 and 5- respectively.
Determined by the switching state of 2. The frequency characteristics of T (jω) for the band rejection type and the high-frequency emphasis type are shown in FIGS. 3 (a) and 3 (b), respectively. In the figure, ω _n , ω
_b is the resonance angular frequency, Q _b represents the selectivity in the case of high-tone-emphasized.

First, in order to obtain the required Q value, the ratio of gm and the ratio of G are determined, and then the absolute value of ω _o is adjusted, whereby the transfer function can be manipulated arbitrarily. BIQU
There are two types of AD circuits (1) and (2) shown in Fig. 4. Here, the S / N (signal / noise ratio) of each type is considered.
Consider. Assuming that in each type of circuit, the value of the capacitor can be ignored in the passband,
The voltage / current converter can be thought of as a high gain A voltage amplifier, and each type of BIQUAD circuit can be represented by the model shown in FIG.

In FIG. 5, for the type (1), the S / N at the output Vout is calculated, assuming that noises n _a and n _b are mixed in the input part of each voltage / current converter.

[0030]

[Equation 8]

Therefore, when Va and Vb are erased and Vout is summarized,

[0032]

[Equation 9]

It becomes Since A ≧ 1, Vout is given by the following equation.

[0034]

[Equation 10]

Therefore, S at the output of type (1)
/ N is given by the following equation.

[0036]

[Equation 11]

The BIQUAD circuit of the type (2) can be obtained in the same manner, and the following equation holds.

[0038]

[Equation 12]

Thus, if Va and Vb are erased and Vout is summarized,

[0040]

[Equation 13]

It becomes Since A ≧ 1, Vout is given by the following equation.

[0042]

[Numerical equation 14]

Therefore, S at the output of type (2)
/ N is given by the following equation.

[0044]

[Equation 15]

As can be seen by comparing equations (11) and (17), in the case of type (2), the noise component n _b mixed in the input of the latter stage is the voltage gain component of the voltage / current converter. It is just suppressed. From this, it can be said that the type (2) is superior to the type (1) in the noise characteristic of the BIQUAD circuit. The above results were used in the embodiment of the present invention shown in FIG.

FIG. 6 shows the voltage / current converter 3-1 (3-2) of FIG.
It is a block diagram of the Example of the BIQUAD circuit when using operational amplifiers 11 and 12 instead of 7-1 (7-2), respectively. In this case, the variable parameter becomes only the gain of the voltage amplifier _{2,6 (G a, G b)} , the circuit also molecules of T (S) S
2 is an all-pole type with 0, and the speed is inferior to the case of FIG. 2 because an operational amplifier is used.
The be replaced with switched capacitor using the CMOS, the same effect can be expected as to vary the gm _a, gm _b in FIG.

FIG. 7 is a circuit diagram of the entire analog filter of the embodiment of the present invention. As shown in the figure, by connecting a plurality of BIQUAD circuits shown in FIG. 2 in cascade, the cutoff characteristic of the filter can be made sharp, and the number can be arbitrarily selected according to the application. Further, it is possible to save energy by turning off the power supply to the unused BIQUAD circuit.

FIG. 8 is a block diagram of the K value setting circuit in the embodiment. The K value setting circuit includes an analog differential amplifier 14 for determining a reference value of K, a circuit 15 including two differential amplifiers for determining a variable portion of K, and one of the two differential amplifiers. And a switch circuit 16 for selecting.

The voltage gain G1 of the differential amplifier 14 at the preceding stage is defined as the internal resistance of the diode D as a load is _reref.

[0050]

[Equation 16]

The gain G2 of the differential amplifier of the circuit 15 in the subsequent stage is
If the internal resistance of the emitter-coupled transistor is r _evar ,

[0052]

[Numerical formula 17]

It becomes From equations (18) and (19), the total gain G, that is | K |

[0054]

[Equation 18]

It becomes Where k is Boltzmann's constant, T
Is absolute temperature, q is electron charge, I _Kref is reference current, I
_Kvar is a variable current. The sign of K can be selected by switching SW.

FIG. 9 is a block diagram of the voltage gain variable circuit in the embodiment. The circuit configuration of FIG. 9 is basically the same as the circuit configuration of FIG. 8 described above, but the switch circuit 16 of FIG. 8 does not exist in FIG. Similarly to the above, the gain G of the circuit of FIG. 9 is given by the following equation.

[0057]

[Formula 19]

Here, I _Gref is a reference current and I _Gvar is a variable current. 10 and 11 are configuration diagrams of the variable voltage / current conversion circuit according to the embodiment. Although FIG. 10 shows the case of a bipolar transistor, the circuit arrangement of FIG even a circuit configuration basically the same as in FIG. 9 described above, the conductance gm of the voltage / current conversion circuit, the current flowing through the I _{RE F} terminal 2I
_{If the} current flowing through the _Iref and _IVAR terminals is 3I _Ivar ,

[0059]

[Equation 20]

Is calculated. As described above, the transfer function of equation (3) can be freely manipulated. In addition, FIG. 11 shows a CMOS
The case of a transistor is shown, but since there is only one control current terminal, gm cannot be varied linearly with respect to the control current I _{VARA (B)} . However, as in the present invention, the non-linearity of gm can be compensated by using it together with a variable gain voltage amplifier. (I _{VARA (B)} is fixed and only G is a variable parameter.)

[0061]

As described above, according to the present invention, various forms of analog signal processing can be dealt with by switching the output of the third voltage gain varying means by the switch means. Also, the first and second voltages /
The transfer function of the filter can be freely created by arbitrarily changing the voltage / current conversion rate and the voltage gain using the current conversion rate variable type integration means and the first, second and third voltage gain variable means. Therefore, it is possible to secure a wider adjustment range than ever before. At the same time, relative variations in the capacitance value of the capacitors can be corrected by the above means.

[Brief description of drawings]

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

FIG. 2 is a block diagram of a BIQUAD circuit according to an embodiment of the present invention,

FIG. 3 is a frequency characteristic diagram of T (jω) in the embodiment,

FIG. 4 is a diagram showing two types of BIQUAD circuits of an example;

5 is a diagram showing a passband model of each type of the BIQUAD circuit of FIG. 4;

FIG. 6 is a block diagram of a BIQUAD circuit according to another embodiment of the present invention,

FIG. 7 is a circuit configuration diagram of an entire analog filter according to an embodiment of the present invention,

FIG. 8 is a configuration diagram of a K value setting circuit in the embodiment,

FIG. 9 is a configuration diagram of a voltage gain variable circuit in the embodiment,

FIG. 10 is a configuration diagram (1) of a variable voltage / current conversion circuit according to an embodiment,

FIG. 11 is a configuration diagram (2) of a variable voltage / current converter circuit according to an embodiment,

FIG. 12 is a configuration diagram of a BIQUAD circuit of a conventional example.

[Explanation of symbols]

 200 is the first voltage gain varying means, 300 is the first voltage / current conversion rate varying type integrating means, 400 is the third voltage gain varying means, 500 is switching means, 600 is second voltage gain varying means, Reference numeral 700 denotes a second voltage / current conversion rate variable type integrating means.

Claims (4)

[Claims] 1. An analog filter using a BIQUAD circuit, wherein the BIQUAD circuit has a phase of a voltage (Vout) fed back from an output of a second voltage / current conversion factor variable type integrating means described later. Is inverted and added to the input voltage (Vin), and the added value is amplified by a variable voltage gain and output.
00), and a first voltage / current conversion rate variable type integration means (300) for converting the output voltage of the first voltage gain variable means into a current with a variable voltage / current conversion rate, and integrating and outputting the current. And inverting the phase of the voltage (Vout) fed back from the output of the second variable voltage / current conversion rate variable integrating means, and adding it to the output of the first voltage / current conversion rate variable integrating means, Second voltage gain varying means (600) for amplifying and outputting the added value with a variable voltage gain, and converting the output voltage of the second voltage gain varying means into a current with a variable voltage / current conversion rate. An analog filter characterized by comprising a second voltage / current conversion rate variable type integrating means (700) which is integrated and then output. 2. The first voltage / current conversion rate variable type integration means and the second voltage / current conversion rate variable type integration means,
The analog filter according to claim 1, wherein the analog filter is an integrating means including a capacitor, a resistor, and an operational amplifier. 3. The analog filter according to claim 1, wherein the input voltage to the first voltage gain varying means is branched and input, and the positive and negative signals are amplified by a variable voltage gain (K). Third voltage gain varying means (400) for outputting
And a switch means (50 for selectively outputting one of the outputs of the third voltage gain varying means by a switching signal from the outside).
0) is provided, and the output of the third voltage gain varying means selected by the switching means is added to the output of the second voltage / current conversion rate varying integrating means. The analog filter according to claim 1. 4. An analog filter composed of the BIQUAD circuit according to claim 1, the third voltage gain varying means according to claim 3 and a switch means is arranged in parallel for differential operation. An analog filter characterized by having a configuration.