JP2002064359A - Compositing method for electronic filter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a compositing method for an electronic filter, with which the electronic filter of less distortion can be provided even when a transconductance amplifier has considerably distorted input voltage/output current characteristics. SOLUTION: The transmission function of the electronic filter is temporarily provided with a one-side terminated ladder filter composed of a coil, a capacitor and a resistor and afterwards, the coil and the resistor are equivalently converted while using the transconductance amplifier. Thus, the electronic filter is composited by transconductance amplifiers 31a-31g and capacitors 32a-32g respectively having the adverse distortion characteristics of about 30 dB.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a low-voltage and high-performance electronic filter used for a front end of a communication and recording system.

[0002]

2. Description of the Related Art Attempts to synthesize an electronic filter on an LSI have been actively studied since the realization of the LSI.
There are various techniques for synthesizing an electronic filter on an LSI, such as a technique using an operational amplifier and a technique using a switched capacitor circuit.

In recent years, with an increase in the speed of communication and recording systems, attempts have been made to realize an electronic filter on an LSI using a voltage-current conversion circuit called a transconductance amplifier. The reason for this is that the transconductance amplifier can relatively easily reduce the power consumption and widen the bandwidth, and is suitable for high-speed signal processing.

In general, there are roughly two methods for implementing an electronic filter (analog filter) on an LSI. First, as shown in FIGS. 6A and 6B, the transfer function of the electronic filter is decomposed into fractional polynomials of second order or less, and each of the fractional polynomials is realized by a transconductance amplifier. Are connected in series, and is a method called a direct synthesis method. The other is a method in which a transfer function of an electronic filter is once realized in a circuit form called a ladder filter including a coil, a capacitance, and a resistance, and then the coil and the resistance are equivalently converted using a transconductance amplifier.

FIG. 7A shows a general equivalent conversion method from the coil L to the transconductance amplifier circuit.
(B) shows a general equivalent conversion method from the resistor R to the transconductance amplifier circuit. 6
1, 62 and 64 are transconductance amplifiers, 6
Reference numeral 3 denotes a capacity. If a transconductance amplifier is used, an equivalent circuit of a coil and a resistor can be easily realized. Therefore, if a passive filter circuit is first synthesized using a coil, a capacitance, and a resistance, and the coil and the resistance are realized by an equivalent circuit using a transconductance amplifier circuit, an electronic filter can be synthesized without using a coil.
Capacitance, resistance and transconductance amplifier can be easily set to L
Since it can be integrated on SI, an electronic filter realized by an equivalent circuit using a transconductance amplifier is:
It is easily realized on an LSI.

What is key in the method of synthesizing the electronic filter is the characteristics of the transconductance amplifier. Transistor elements used in transconductance amplifiers inherently exhibit strong nonlinearity in input voltage vs. output current characteristics, so transconductance amplifiers designed using such transistors sufficiently eliminate the nonlinearity and provide input voltage vs. output current characteristics. Had to be linearized. FIG.
(B) shows a circuit example of the linearized transconductance amplifier. 51 is a first input terminal, and 52 is a second input terminal.
Input terminals, 53a to 53d are NMOS transistors, 5
4a to 54b are PMOS transistors, 55 is a current bias voltage input terminal, 56 is a first output terminal, and 57 is a second output terminal.

[0007]

As described above, the transconductance amplifier used so far has been devised in various circuits in order to make the distortion characteristics as good as possible. As a result, the transconductance amplifier became complicated, resulting in passing through a plurality of transistors from the signal input terminal to the signal output terminal. 5B, two transistors 53a and 53c are provided on the path from the first input terminal 51 to the first output terminal 56, and the two transistors 53a and 53c are connected from the second input terminal 52 to the second output terminal 57. Two transistors 53b and 53d on the path to
Respectively intervene. In general, the longer the time it takes to pass through a transconductance amplifier, the lower the bandwidth of an electronic filter synthesized using the transconductance amplifier. Therefore, when trying to suppress the distortion, the band of the electronic filter is reduced. Further, in the transconductance amplifier aiming at low distortion, which is composed by stacking a plurality of transistors in the vertical direction, there is a problem that it is difficult to reduce the voltage of the power supply.

On the other hand, due to the recent remarkable improvement in signal processing speed of magnetic recording devices represented by hard disk drives, the bandwidth of these electronic filters has been approaching the limit at present and has been adapted to the bandwidth of the electronic filters. There is a need for a new electronic filter synthesis method.

[0009]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a method of synthesizing an electronic filter capable of realizing an electronic filter with less distortion even when the transconductance amplifier has greatly distorted input voltage-output current characteristics. It is in. In other words, the inventor of the present application views the viewpoint of the synthesis method from a different angle from the conventional one, and when the distortion characteristics of the transconductance amplifier are extremely poor, which electronic filter synthesis method has the best distortion characteristics. The present invention has been studied to determine whether or not it will bring about, and a method for synthesizing an electronic filter according to the present invention is conceived.

More specifically, the invention of claim 1 is:
In a method for synthesizing an electronic filter using a transconductance amplifier that converts an input voltage to an output current at a desired conversion rate, a step of realizing a transfer function of the electronic filter with a one-sided terminal ladder-type filter including a coil, a capacitor, and a resistor. The coil and the resistor of the one-sided terminal ladder type filter,
Equivalent using a transconductance amplifier having a characteristic that the ratio of the signal intensity of the 0th-order main signal is 100 times or less as compared with the signal intensity of the root mean square due to the second and higher harmonics included in the output current. And a converting step.

According to a second aspect of the present invention, there is provided a method for synthesizing an electronic filter using a transconductance amplifier for converting an input voltage to an output current at a desired conversion rate, wherein the transfer function of the electronic filter is a one-sided circuit comprising a coil, a capacitor, and a resistor. A transconductance amplifier having a configuration in which the step of realizing the terminal ladder type filter and the coil and the resistance of the one-sided terminal ladder filter each include only a single transistor on a path from a signal input terminal to a signal output terminal. And a step of performing equivalent conversion by using the following.

According to a third aspect of the present invention, in the electronic filter synthesizing method according to any one of the first and second aspects of the present invention, all the transconductance amplifiers used in the electronic filter have the same input voltage to output current characteristics. It is what it was.

[0013]

According to the method of synthesizing an electronic filter according to the present invention, the transfer function of the electronic filter is once realized by a one-sided terminal ladder filter composed of a coil, a capacitor and a resistor, and then the coil and the resistor are transconducted. Equivalent conversion is performed using an amplifier.

FIG. 1A shows an example of a one-sided terminal ladder type filter used in the method of synthesizing an electronic filter according to the present invention, and FIG. 1B shows a double-sided terminal ladder type filter as a comparative example. . In the figure, L represents a coil, C represents a capacitance, and R represents a resistance. That is, the one-sided terminal ladder type filter used in the present invention is a filter in which only the output end is resistance-terminated.

FIG. 2A shows the frequency characteristics of each voltage node of the one-sided terminal ladder filter, and FIG. 2B shows the frequency characteristics of each voltage node of the two-sided terminal ladder filter. As shown in FIG. 2A, the one-sided terminal ladder filter has a feature that all voltage nodes have substantially the same frequency characteristics. Therefore, if a one-sided terminal ladder type filter is employed in the synthesis of the electronic filter, the input / output gains of all the transconductance amplifiers can be made close to one.

At this time, even if the output current characteristic of the transconductance amplifier is distorted, the equivalent resistance using the transconductance amplifier connected to the output voltage terminal is similarly distorted. Is done. As a result, good distortion characteristics can be obtained even when a transconductance amplifier having large distortion is used.

Here, the principle of reducing distortion will be described with reference to FIG. Let the voltage-current conversion characteristic of the transconductance amplifier be I = g (v). Since the first transconductance amplifier 10 converts the input voltage Vin into the output current I1, the relationship is I1 = g (Vin). Then, since the second transconductance amplifier 20 outputs I1, the relationship with the voltage value Vout is Vout.
= G ^-1 (I1). Therefore, the relationship between the input and output voltages is Vout = g ^-1 (g (Vin)) = Vin, and it can be seen that no distortion occurs in the input and output voltages. This relationship is established when the input / output characteristics of the two transconductance amplifiers 10 and 20 are equal including the frequency characteristics. In other words, when the electronic filter is synthesized, if all nodes can have similar frequency characteristics, no distortion occurs in the input / output voltage even if the input voltage-output current characteristic is distorted. I understand.

In the conventional method of synthesizing an electronic filter, either a direct synthesis method or a conversion method from a double-ended ladder type filter has been generally used. This is because the frequency characteristics are less likely to be affected by manufacturing variations in the two-sided terminal ladder type filter than in the one-sided terminal ladder type filter because the element sensitivity is lower. That is, the one-sided terminal ladder filter was not of any interest. However, the one-sided terminal ladder filter has the characteristic that the frequency characteristics at all voltage nodes are almost equal as shown in FIG. 2A as described above. On the other hand, as shown in FIG. 2B, the frequency characteristics of each node of the double-sided terminal ladder filter are unlikely to be equal to each other. The same can be said for a case where an electronic filter is synthesized by a direct synthesis method.

The present invention is the first filter synthesis method focusing on the above characteristics of a one-sided terminal ladder filter. Further, even if there is an example in which an electronic filter is synthesized from a one-sided terminal ladder type filter, it is not used for the purpose of reducing distortion characteristics. That is, until now, there is no example in which a low-distortion electronic filter is synthesized from a one-sided terminal ladder-type filter using a transconductance amplifier having extremely poor distortion characteristics. In short, the feature of the method for synthesizing an electronic filter in the present invention is that the distortion characteristics of the electronic filter itself are better than the distortion characteristics of the transconductance amplifier used.

FIG. 4 shows an example of an electronic filter obtained by the synthesizing method according to the present invention. 31a-31
g denotes a transconductance amplifier, and 32a to 32g denote capacitances.

According to the present invention, there is no need to pay attention to the distortion characteristics of the transconductance amplifier used for synthesizing the electronic filter as in the prior art. Therefore, it is possible to use a transconductance amplifier having a very simple configuration, and as a result, it is possible to realize an electronic filter having a wider band than before.

FIG. 5A shows an example of a transconductance amplifier used in the method for synthesizing an electronic filter according to the present invention. 41 is a first input terminal, 42 is a second input terminal,
43a-43b are NMOS transistors, 44a-44
b is a PMOS transistor, 45 is a first output terminal, 46
Denotes a second output terminal, and 47 denotes a current bias voltage input terminal.

The transconductance amplifier shown in FIG. 5A has a configuration in which only one transistor exists between the input and output terminals. Therefore, the time that the signal passes through the transconductance amplifier is minimal. According to the filter theory when synthesizing an electronic filter, the shorter the time it takes to pass through the inside of the transconductance amplifier, the more it is possible to realize an electronic filter having a wider band. Therefore, an electronic filter synthesized using a transconductance amplifier as shown in FIG. 5A has a wider band than a conventional electronic filter. However, since such a transconductance amplifier has very poor input / output distortion characteristics (about 30 dB), the distortion characteristics cannot be improved by a conventional filter synthesis method. Therefore, a filter using this transconductance amplifier is realized. I never did. However, if the method for synthesizing an electronic filter according to the present invention is used, the distortion characteristics can be improved, so that a transconductance amplifier as shown in FIG. 5A can be used, and as a result, a transconductance amplifier having a wider band than before can be realized. It is possible to

The fact that a transconductance amplifier having a wider band than the conventional one can be realized means that it is possible to synthesize an electronic filter having the highest power efficiency from another point of view. If used, an electronic filter with the lowest power consumption can be realized when electronic filters having similar bands are combined. However, the transconductance amplifier used in the electronic filter synthesis method according to the present invention is shown in FIG.
However, the present invention is not limited to the configuration shown in FIG. 1, but any transconductance amplifier having a very bad distortion characteristic can be employed.

[0025]

As described above, according to the present invention,
An electronic filter is provided by replacing a coil and a resistance of a one-sided terminal ladder filter composed of a coil, a capacitance and a resistance with an equivalent circuit using a transconductance amplifier.
At this time, since the frequency characteristics of all the voltage nodes of the converted electronic filter are almost the same, the transconductance amplifier connected to the output voltage terminal was used even if the output current characteristics of the transconductance amplifier were distorted. Since the equivalent resistance is similarly distorted, the distortion characteristic is canceled and a voltage is output. As a result, good distortion characteristics can be obtained even when a transconductance amplifier having large distortion is used.

According to the present invention, an electronic filter can be synthesized using a transconductance amplifier having a very simple structure in which at most one transistor exists between input and output terminals. It is possible to synthesize a broadband electronic filter.

[Brief description of the drawings]

FIG. 1A is a circuit diagram illustrating an example of a one-sided terminal ladder type filter used in a method of synthesizing an electronic filter according to the present invention, and FIG.

2A is a diagram illustrating frequency characteristics of each voltage node of a one-sided terminal ladder filter, and FIG. 2B is a diagram illustrating frequency characteristics of each voltage node of a two-sided terminal ladder filter.

FIG. 3 is a block diagram for explaining the principle of distortion reduction according to the present invention.

FIG. 4 is a block diagram illustrating an example of an electronic filter obtained by a synthesis method according to the present invention.

FIG. 5A shows an example of a transconductance amplifier used in the method for synthesizing an electronic filter according to the present invention;
FIG. 2B is a circuit diagram illustrating an example of a transconductance amplifier used in a conventional method of synthesizing an electronic filter.

FIGS. 6A and 6B are conceptual diagrams for explaining a method of synthesizing an electronic filter based on a conventional direct synthesis method.

7A is a conceptual diagram illustrating a general equivalent conversion method from a coil to a transconductance amplifier circuit, and FIG. 7B is a conceptual diagram illustrating a general equivalent conversion method from a resistor to a transconductance amplifier circuit.

[Explanation of symbols]

 10, 20 transconductance amplifier 31a to 31g transconductance amplifier 32a to 32g capacitance 41 first input terminal 42 second input terminal 43a to 43b NMOS transistor 44a to 44b PMOS transistor 45 first output terminal 46 second output terminal 47 current bias voltage Input terminal 51 First input terminal 52 Second input terminal 53a to 53d NMOS transistor 54a to 54b PMOS transistor 55 Current bias voltage input terminal 56 First output terminal 57 Second output terminal 61, 62, 64 Transconductance amplifier 63 Capacity C capacity L coil R resistance

 ──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Hirokuni Fujiyama 1006 Kadoma Kadoma, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. F term (reference) 5J098 AA03 AA14 AB03 AD12 CA02 CB01 CB08

Claims (3)

[Claims] 1. A method for synthesizing an electronic filter using a transconductance amplifier for converting an input voltage into an output current at a desired conversion rate, wherein a transfer function of the electronic filter is a one-sided terminal ladder comprising a coil, a capacitor, and a resistor. A filter realized by a filter, and a coil and a resistor of the one-sided terminal ladder type filter each having a zero-order main signal of a zero-order main signal compared with a signal intensity of a root-mean-square value of a second-order or higher total harmonic included in the output current. Performing equivalent conversion using a transconductance amplifier having a characteristic that a signal intensity ratio is 100 times or less. 2. A method for synthesizing an electronic filter using a transconductance amplifier for converting an input voltage to an output current at a desired conversion rate, wherein a transfer function of the electronic filter is a one-sided terminal ladder comprising a coil, a capacitor, and a resistor. A step of realizing the filter, the coil and the resistance of the one-sided terminal ladder filter, using a transconductance amplifier having a configuration in which only a single transistor is interposed on the path from the signal input terminal to the signal output terminal. Performing an equivalent conversion. 3. The method for synthesizing an electronic filter according to claim 1, wherein all of the transconductance amplifiers used in the electronic filter have the same input voltage to output current characteristics. A method for synthesizing an electronic filter.