JPH08274581A - Analog filter - Google Patents

Abstract

PURPOSE: To obtain target frequency characteristic even when manufacturing dispersion exists in a resistor in an analog filter formed with the resistor and a capacitor on a semiconductor substrate. CONSTITUTION: A reference voltage generation circuit 26 which generates a constant output voltage as a reference voltage Vb in spite of the manufacturing dispersion of the resistor, and a voltage conversion circuit 25 in which an output voltage (comparison voltage) Vc is varied due to the manufacturing dispersion of the resistor 17 are provided. The reference voltage Vb is compared with the comparison voltage Vc by a comparator 19, and the manufacturing dispersion of the resistor 17 (in other words, the resistors 6, 7 which comprise the analog filter) is detected. When the resistance value of the resistor 17 is larger than a reference value, the output of the comparator 19 goes to an 'L' level, and transistors 11-14 are turned on. Consequently, since the resistors 11-14 are connected in parallel with the resistors 6, 7, a total resistance value which comprises the analog filter is reduced, and the frequency characteristic of the analog filter is corrected, then, the target frequency characteristic is obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improved analog filter formed on a semiconductor substrate.

[0002]

2. Description of the Related Art In recent years, due to advances in semiconductor integrated circuit technology, analog filters that were conventionally external circuits have become
With the aim of reducing the number of external parts and reducing the cost, the semiconductor device is constructed on a semiconductor substrate, and the importance of its integration technology has increased.

A conventional analog filter formed on a semiconductor substrate will be described below by taking an analog low pass filter as an example.

FIG. 3 is a block diagram of a conventional analog low pass filter formed on a semiconductor substrate. In the analog low-pass filter shown in the figure, 1 and 2 are resistors made of polysilicon or a diffusion layer, 3 and 4 are capacitors made of an oxide film and polysilicon, 5 is an operational amplifier, and IN is an input terminal. , OUT are output terminals. The two resistors 1 and 2 are connected in series between the input terminal IN and the operational amplifier 5, and the capacitance 3 is connected to the input of the operational amplifier 5 and G.
The other capacitance 4 is connected between ND (ground) and the output of the operational amplifier 5 and the connection line between the two resistors 1 and 2.

[0005]

However, in the above-mentioned conventional structure, when the values of the resistors 1 and 2 vary due to manufacturing variations, the product CR of the resistance value and the capacitance value CR.
As a result, when the product CR of the resistance value and the capacitance value becomes larger than the target value as shown by the broken line in the frequency characteristic of FIG. 4, the target frequency shown by the solid line in FIG. There is a problem that the band is narrowed by shifting to the left side of the characteristic, while the band is narrowed when it is smaller than the target value, the band is widened by shifting to the right side of the target frequency characteristic.

The present invention is intended to solve the above problems, and an object of the present invention is to provide an analog filter having a resistor and a capacitor whose frequency characteristic is substantially the target frequency even if the resistance value of the resistor varies due to manufacturing variations. It is to provide an analog filter whose characteristics are fixed.

[0007]

In order to achieve the above object, according to the present invention, a frequency characteristic correction circuit for correcting the frequency characteristic when the frequency characteristic fluctuates due to manufacturing variations of resistors is provided. .

That is, the analog filter according to claim 1 is an analog filter which is formed on a semiconductor substrate and is composed of a resistor and a capacitor, and a variation detecting circuit for detecting a variation in manufacturing of the resistor, and the variation. And a frequency characteristic correction circuit that corrects the frequency characteristic according to the manufacturing variation detected by the detection circuit.

According to a second aspect of the present invention, in the analog filter according to the first aspect, the variation detection circuit corresponds to a voltage conversion circuit for converting the production variation of the resistor into a voltage and the resistor having no production variation. It is characterized by comprising a reference voltage generation circuit for generating a reference voltage, and a comparison circuit for comparing the voltage converted by the voltage conversion circuit with the reference voltage generated by the reference voltage generation circuit.

Further, in the invention described in claim 3, in the analog filter described in claim 2, the voltage conversion means is connected between the constant current source connected to the ground and the constant current source and the power source. And a resistor for converting manufacturing variation of the resistor into a voltage between the resistor and a constant current source. The reference voltage generating circuit includes two resistors connected in series between a power source and a ground. And a voltage divided by the two resistors as a reference voltage is generated, and the comparison circuit uses a voltage between the resistance of the voltage conversion means and the constant current source as a comparison voltage, It is characterized by comprising a comparator for comparing the comparison voltage with the reference voltage of the reference voltage generating circuit.

In addition, the invention according to claim 4 is the analog filter according to claim 1, claim 2 or claim 3, wherein the frequency characteristic correction circuit adjusts the resistance value of the resistor. The resistance value adjusting circuit adjusts the resistance value of the resistor according to the manufacturing variation detected by the variation detecting circuit to correct the frequency characteristic.

According to a fifth aspect of the present invention, in the analog filter according to the fourth aspect, the resistance value adjusting circuit comprises a transistor arranged in parallel with the resistor, and the transistor is detected by the variation detecting circuit. It is characterized in that the ON / OFF operation is performed according to the manufacturing variation.

[0013]

With the above structure, in the inventions according to the first to fifth aspects, the variation detecting circuit detects the manufacturing variation of the resistor, and the manufacturing variation varies in the increasing direction of the resistance value according to the manufacturing variation of the resistor. In Case of,
The frequency characteristic correction circuit corrects to reduce the resistance value of the resistor, for example, to obtain almost the target frequency characteristic, and
On the contrary, when the detected manufacturing variation is in the decreasing direction of the resistance value, the frequency characteristic correcting circuit corrects the resistance value of the resistor to increase, for example, and the target frequency characteristic is obtained.

[0014]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a concrete configuration diagram of an analog low-pass filter which is an embodiment of the present invention.

In the figure, 6, 7, 15, 16 and 1
7 is a resistor made of polysilicon or a diffusion layer, 8 and 9 are capacitors made of an oxide film and polysilicon, 10 is an operational amplifier, and 11 and 12 are P-channel M.
OS transistors, 13 and 14 are N-channel MO
S-transistor, 18 is a constant current source, 19 is a comparator, 20 is an inverter, 21 is a power source having a predetermined voltage, IN is an input terminal, and OUT is an output terminal.

The two resistors 6 and 7 are connected to the input terminal IN.
And the operational amplifier 10 are connected in series, the capacitance 8 is connected between the input of the operational amplifier 10 and GND, and the other capacitance 9
Is connected to the connection line between the output of the operational amplifier 10 and the two resistors 6 and 7.

The resistor 17 has the same manufacturing variation as the resistors 6 and 7 forming the analog low pass filter. The resistor 17 and the constant current source 18 are connected in series, and the resistor 17 is connected to the power source 21. Connected, the constant current source 18 is G
Connected to ND. The voltage Vc output between the resistor 17 and the constant current source 18 is the absolute value of the resistor 17, that is, the resistor 1
The voltage Vc varies depending on the manufacturing variation of No. 7, and is used as a comparison voltage. With these configurations, the voltage conversion circuit 25 that converts the manufacturing variation of the resistor 17 into the voltage Vc is configured.

The two resistors 15 and 16 are connected in series to the power source 21 and the GND. The divided voltage Vb of the two resistors 15 and 16 is
Even if the absolute value of the resistance value of 6 varies due to manufacturing variations, it is determined by the resistance ratio. Therefore, this divided voltage Vb is always constant regardless of manufacturing variations. This constant voltage Vb is used as a reference voltage. With this configuration, the reference voltage generation circuit 26 that generates the reference voltage Vb corresponding to the resistance without manufacturing variation is configured.

The comparator (comparison circuit) 19 has its (+) terminal connected to the comparison voltage Vc from the voltage conversion circuit 25.
Is input to the (−) terminal of the reference voltage generation circuit 2
The reference voltage Vb of 6 is input. The comparator 19 is
When the value of the resistor 17 becomes larger than the target resistance value, that is, when the comparison voltage Vc becomes smaller than the reference voltage Vb, "L".
Outputs the level output voltage.

The voltage conversion circuit 25, the reference voltage generation circuit 26, and the comparator (comparison circuit) 19 make the resistance 1
A variation detection circuit 27 for detecting the manufacturing variation of No. 7 is configured.

The two P-channel MOS transistors 11 and 12 are connected in parallel with the two resistors 6 and 7 in a state of being connected in series to form a transfer gate and each gate thereof. The output of the comparator 19 is directly input to. Similarly, the above 2
The N-channel MOS transistors 13 and 14 are
The above two P-channel MOSs connected in series
The transfer gates are connected in parallel with the transistors 11 and 12 to form another transfer gate, and the output of the comparator 19 is input to each gate via the inverter 20. With the above configuration, the resistance value adjusting circuit 30 for adjusting the resistance values of the two resistors 6 and 7 is configured, and the resistance value adjusting circuit 30 adjusts the manufacturing variation of the resistor 17 detected by the variation detecting circuit 27. Accordingly, the resistance value of the two resistors 6 and 7 is adjusted, and the frequency characteristic correction circuit 31 is configured to correct the frequency characteristic of the analog low-pass filter.

Therefore, in this embodiment, the resistance 1
When the value of 7 is larger than the target resistance value and the comparison voltage Vc is smaller than the reference voltage Vb, the output voltage of "L" level is output from the comparator 19 and each of the P-channel and N-channel MOS transistors is output. 11-14
(Transfer gate) is turned on, so these 11
14 is connected in parallel to the resistors 6 and 7, and the values of the resistors 6 and 7 forming the analog low pass filter are lowered.

Therefore, when the values of the resistors 6 and 7 constituting the analog low-pass filter become larger (manufactured larger) than the target value due to manufacturing variations, the product CR of the resistance value and the capacitance value also becomes large. The frequency characteristic of the analog low-pass filter deviates to the left side in the figure as shown by the broken line in the figure with respect to the target frequency characteristic shown by the solid line in FIG. Since the resistance values of the resistors 6 and 7 of the analog low pass filter are corrected to be small by the parallel connection of the transistors 11 to 14), the frequency characteristic is corrected as shown by the alternate long and short dash line in FIG. Can be approached to.

In this embodiment, the case where the reference voltage Vb is one kind and therefore the resistance values of the resistors 6 and 7 can be changed only in two steps has been described. However, the present invention is not limited to this and the reference Since the resistance values of the resistors 6 and 7 can be changed to n + 1 steps by having a plurality of (n) the voltage Vb, the comparator 19 and the transfer gate group, it is possible that the manufacturing variation of the resistors is on the increasing side of the resistance value. Finer adjustments can be made when both are on the decrease side.

In this embodiment, the analog low-pass filter has been described as an example, but the present invention is also applicable to the analog high-pass filter and the analog band-pass filter which are composed of the resistor and the capacitor on the semiconductor substrate. Of course, it can be applied to.

[0027]

As described above, according to the analog filter of the first to fifth aspects, even if there is a manufacturing variation in the resistance which is the constituent element, the resistance value is appropriately adjusted, The frequency characteristic can be fixedly held at the target frequency characteristic.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing an analog low-pass filter according to an embodiment of the present invention.

FIG. 2 is a diagram showing frequency characteristics of the analog low-pass filter according to the embodiment of the present invention.

FIG. 3 is a circuit diagram showing a conventional analog low-pass filter.

FIG. 4 is a diagram showing frequency characteristics of a conventional analog low-pass filter.

[Explanation of symbols]

 6,7 resistance 8,9 capacitance 10 operational amplifier 11 P-channel MOS transistor 12 P-channel MOS transistor 13 N-channel MOS transistor 14 N-channel MOS transistor 15,16 resistance 17 resistance 18 constant current source 19 comparator (comparison circuit) 21 power supply 25 voltage Conversion circuit 26 Reference voltage generation circuit 27 Variation detection circuit 30 Resistance value adjustment circuit 31 Frequency characteristic correction circuit

Claims (5)

[Claims] 1. An analog filter formed of a resistor and a capacitor formed on a semiconductor substrate, comprising: a variation detection circuit for detecting variation in manufacturing of the resistor; and a variation in manufacturing detected by the variation detecting circuit. An analog filter comprising: a frequency characteristic correction circuit that corrects the frequency characteristic according to the above. 2. The variation detection circuit includes a voltage conversion circuit for converting a manufacturing variation of a resistor into a voltage, a reference voltage generating circuit for generating a reference voltage corresponding to a resistor having no manufacturing variation, and the voltage conversion circuit for converting the reference voltage. The analog filter according to claim 1, further comprising a comparison circuit for comparing the generated voltage with the reference voltage generated by the reference voltage generation circuit. 3. The voltage converting means comprises a constant current source connected to the ground and a resistor connected between the constant current source and the power source. The reference voltage generating circuit is composed of two resistors connected in series between the power source and the ground, and the voltage divided by the two resistors is used as a reference. The comparator circuit is composed of a comparator for comparing the voltage between the resistance of the voltage converting means and the constant current source as a comparison voltage, and comparing the comparison voltage with the reference voltage of the reference voltage generating circuit. The analog filter according to claim 2, wherein: 4. The frequency characteristic correction circuit comprises a resistance value adjustment circuit for adjusting the resistance value of the resistor, and the resistance value adjustment circuit adjusts the resistance value of the resistance in accordance with the manufacturing variation detected by the variation detection circuit. The analog filter according to claim 1, 2 or 3, wherein the analog filter is adjusted to correct the frequency characteristic. 5. The resistance value adjusting circuit is composed of a transistor arranged in parallel with the resistor, and the transistor has an O-value according to the manufacturing variation detected by the variation detecting circuit.
The analog filter according to claim 4, wherein the analog filter is operated N / OFF.