JP2007282360A - Smoothing circuit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a smoothing circuit whose cut-off frequency can easily be changed by a user. <P>SOLUTION: The smoothing circuit, which is provided on a semiconductor integrated circuit, comprises resistance elements and capacitance elements. The smoothing circuit includes a first parallel circuit, in which the resistance elements are connected in parallel to a switch, when the cut-off frequency is set. Also, the resistance value of the first parallel circuit is selected by the capacity value and size of the capacitance elements. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a technique for adjusting a cutoff frequency of a smoothing circuit provided in a semiconductor integrated circuit.

  In recent years, IC chips (semiconductor integrated circuits) have been required to reduce the number of peripheral components as well as to reduce the cost and size. For example, in order to obtain a necessary signal by integrating an RF signal (Radio Frequency) or the like, a low pass filter is generally used when performing smoothing. It is known that the configuration of the low-pass filter in such a case includes a resistance element and a capacitance element. The resistor element and the capacitor element used for the low-pass filter are mounted on a board manufactured by the user as external components of the IC chip.

  However, it is known that in order to set the cut-off frequency of the low-pass filter low, the resistance element used, the resistance value of the capacitance element, and the capacitance value increase. Nowadays, such a problem can be dealt with to some extent because the chip size of the resistive element and the capacitive element is reduced due to technological advancement. As a result, the user can easily design the layout even when the IC chip and its external parts are used.

In addition, with such progress, attempts have been made to incorporate resistance elements and capacitive elements in the IC chip.
The case of the circuit shown in FIG. 5 will be described. The circuit shown in FIG. 5 includes a full-wave rectifier circuit 51, a buffer circuit 52, a capacitor element 53 (external component), a resistor element 54, a comparison detection circuit 55, a DC bias voltage source 56, and a threshold voltage source 57. Yes.

  For example, the input signal is full-wave rectified by the full-wave rectifier circuit 51, the signal is output via the buffer circuit 52, and smoothed by the capacitive element 53 and the resistive element 54. Thereafter, the comparison detection circuit 55 compares the smoothed signal with the threshold voltage supplied from the threshold voltage source 57. In the case of such a circuit, it is necessary for the user to prepare the normal capacitive element 53 as an external component.

According to Patent Documents 1 and 2, there are proposals for reducing the number of external parts.
Japanese Patent Application Laid-Open No. 06-77851 JP 2000-332603 A

  However, in the prior art, a proposal for reducing the number of external parts has been made, but when the user changes the capacitance element 53 of the smoothing circuit and sets the cutoff frequency, the resistance value of the resistance element 54 is reduced. Must be changed. Further, when the capacitive element 53 and the resistive element 54 are built in the IC chip, there is a problem that the user cannot change the setting of the cutoff frequency.

  The present invention has been made in view of the above circumstances, and an object thereof is to provide a smoothing circuit in which a user can easily change the setting of the cutoff frequency.

A smoothing circuit provided in a semiconductor integrated circuit which is one aspect of the present invention,
A first parallel circuit capable of switching a resistance value by connecting the first resistance element and a switch in parallel when the smoothing circuit is configured by a first resistance element and a capacitance element to set a cutoff frequency; The resistance value of the first parallel circuit is selected according to the capacitance value and size of the capacitive element.

  Preferably, when the output voltage of the smoothing circuit changes due to the change of the resistance value, a resistance element and a switch are connected in parallel to switch the output voltage so that the voltage value before the change is obtained. It is good also as a structure which provides the 2nd parallel circuit which can switch.

  Preferably, when the output of the smoothing circuit is connected to one input of the comparison detection circuit, a resistance element and a switch are connected in parallel to control the voltage of the other input of the comparison detection circuit. It is good also as a structure which provides the 3rd parallel circuit which can switch a value.

  Preferably, the first parallel circuit, the second parallel circuit, and the third parallel circuit of the smoothing circuit may be variable resistance elements, and the capacitive elements may be variable capacitance elements.

Preferably, the first parallel circuit, the second parallel circuit, the variable resistance element of the third parallel circuit, and a control unit that controls the variable capacitance element may be provided.
With the above configuration, since the resistance value of the resistance element and the capacitance value of the capacitance element can be changed, the cut-off frequency of the smoothing circuit can be adjusted, and the peripheral circuit of the smoothing circuit can be adjusted to the parameters of the peripheral circuit suitable for the smoothing circuit. Can be changed.

  According to the present invention, it is possible to easily adjust the cutoff frequency of the smoothing circuit, and it is not necessary to consider the limitation due to the size of the resistance element and the capacitive element constituting the smoothing circuit and its peripheral circuit.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
Example 1
The circuit shown in FIG. 1 includes a full-wave rectifier circuit 1, a buffer circuit 2, a first resistor element 3, a first switch 4, a capacitor element 5, a second resistor element 6, a second switch 7, a third resistor element 8, and a DC. It comprises a bias voltage source 9, a comparison detection circuit 10, and a threshold voltage source 11.

The full-wave rectification circuit 1 performs full-wave rectification on the input signal and outputs a full-wave rectification signal to the buffer circuit 2 at the next stage. Thereafter, the buffer circuit 2 outputs an output signal to the smoothing circuit.
The first resistance element 3, the first switch 4, and the capacitive element 5 constituting the smoothing circuit (low-pass filter in this example) smoothes the output signal of the buffer circuit 2 and outputs a smooth signal.

  Next, the second resistance element 6, the second switch 7, and the third resistance element 8 apply the DC bias voltage supplied from the DC bias voltage source 9 to the smooth signal input to the + input terminal of the comparison detection circuit 10. adjust. The threshold voltage source 11 supplies a comparison signal to the negative input terminal of the comparison detection circuit 10 and compares the smooth signal with the comparison signal.

Here, the third resistance element 8 may not be provided, that is, may be provided to determine the minimum resistance value. When the third resistance element 8 is inserted, the step (resolution) can be set small.
Next, the difference from the conventional FIG. 5 is that a first parallel circuit in which a first resistance element 3 and a first switch 4 are connected in parallel is provided at the output stage of the buffer circuit 2. A second parallel circuit in which the second resistance element 6 and the second switch 7 are connected in parallel is connected in series with the third resistance element 8. The other side of the second parallel circuit is connected to the capacitive element 5.

For example, when the output impedance of the buffer circuit 52 of FIG. 5 is 300 kΩ, and the cutoff frequency = 0.53 Hz, the capacitance value of the external capacitive element 53 is 1 μF.
When the resistance value of the first resistive element 3 of the first parallel circuit shown in FIG. 1 is 3 MΩ, the capacitance value of the capacitive element 5 is 1/10 times. That is, 0.1 μF is sufficient.

  However, the voltage at the + input of the comparison detection circuit 10 is different from the circuit shown in FIG. Therefore, it is necessary to adjust the + input voltage. Therefore, it is necessary to adjust to an appropriate voltage by the second resistance element 6 of the second parallel circuit.

  That is, if the first resistance element 3 shown above is set to 3 MΩ, the voltage at the + terminal of the comparison detection circuit 10 shifts, so the resistance of the second resistance element 6 of the second parallel circuit must be changed. . In this example, the second resistance element 6 is 44 kΩ, and the third resistance element 8 is 33 kΩ.

Next, considering the layout in the chip, even if the resistance value of the first resistive element 3 of the first parallel circuit is increased, the size of the resistive element does not become larger than that of the capacitive element. On the contrary, the size of the capacitive element 5 Since the capacitance value can be reduced as the capacitance value becomes smaller, the capacitance element can be incorporated inside.
(Example 2)
Further, a resistance element for varying the threshold voltage is prepared in the comparison detection circuit 10 in the first embodiment. 2 includes a full-wave rectifier circuit 1, a buffer circuit 2, a first resistor element 3, a first switch 4, a capacitor element 5, a second resistor element 6, a second switch 7, a third resistor element 8, and a DC bias. The voltage source 9, the comparison detection circuit 10, the threshold voltage source 11, the fourth resistance element 12, and the third switch 13 are included.

  In this example, a third parallel circuit for connecting the fourth resistance element 12 and the third switch 13 in parallel is provided. The fourth resistance element 12 controls the voltage of the threshold voltage supplied from the threshold voltage source 11 that is input to the negative terminal of the comparison detection circuit 10. In this case, the third switch 13 may be short-circuited as described above.

By configuring in this way, the range for further adjustment is expanded.
(Example 3)
Next, Embodiment 3 is shown in FIG. 3 for the case where a resistance element and a capacitance element are built in an IC chip. The first resistance element 3, the second resistance element 6, and the fourth resistance element 12 according to the second embodiment can be adjusted as the first variable resistance element 14, the second variable resistance element 16, and the third variable resistance element 17 to be incorporated. To. Further, the capacitive element 5 of the second embodiment is changed to the first variable capacitive element 15.

The variable resistance is switched by a switch or the like by connecting a plurality of resistance elements in series or in parallel. It may be switched by a transistor. The same applies to the variable capacitance element. The current source may be controlled.
Example 4
Adjustment is performed by providing a control unit 22 so that the third embodiment can be further automatically adjusted. The controller 22 can change the resistance value and the capacitance value for automatic adjustment. The fourth variable resistance element 18, the second variable capacitance element 19, the fifth variable resistance element 20, and the sixth variable resistance element 21 can be adjusted by the control unit 22.

  The control unit 22 is connected to the fourth variable resistance element 18, the second variable capacitance element 19, the fifth variable resistance element 20, and the sixth variable resistance element 21, and adjusts the resistance value and the capacitance value according to a signal from the control unit 22. . Further, the input value and the output value are measured by an adjustment device provided outside, and data to be adjusted is generated based on the result. The resistance element and the capacitance element are varied by transferring the data to the control unit 22 and decoding the data.

  With this configuration, automatic adjustment is possible and adjustment time can be reduced. Further, the fourth variable resistance element 18, the second variable capacitance element 19, the fifth variable resistance element 20, the sixth variable resistance element 21, and the control unit 22 may be incorporated in the IC chip.

Further, the present invention is not limited to the low-pass filter, and a band-pass filter or a high-pass filter may be used.
The present invention is not limited to the above-described embodiment, and various improvements and modifications can be made without departing from the gist of the present invention.

1 is a diagram illustrating a circuit of Example 1. FIG. FIG. 6 is a diagram illustrating a circuit according to a second embodiment. FIG. 6 is a diagram illustrating a circuit according to a third embodiment. FIG. 6 is a diagram illustrating a circuit according to a fourth embodiment. It is a figure which shows the conventional circuit.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Full wave rectifier circuit, 2 ... Buffer circuit, 3 ... 1st resistance element 4 ... 1st switch, 5 ... Capacitance element, 6 ... 2nd resistance element 7 ... Second switch, 8... Third resistance element, 9... DC bias voltage source 10... Comparison detection circuit, 11. 3rd switch 14 ... 1st variable resistance element, 15 ... Variable capacitance element 16 ... 2nd variable resistance element, 17 ... 3rd variable resistance element 18 ... 4th variable resistance element, 19 ... 2nd variable capacitance element 20 ... 5th variable resistance element, 21 ... 6th variable resistance element 22 ... Control part

Claims (5)

A smoothing circuit provided in a semiconductor integrated circuit,
A first parallel circuit capable of switching a resistance value by connecting the first resistance element and the first switch in parallel when the smoothing circuit is configured by a first resistance element and a capacitance element to set a cutoff frequency. And a resistance value of the first parallel circuit is selected according to a capacitance value and a size of the capacitive element.   When the output voltage of the smoothing circuit changes due to the change of the resistance value, a second resistor element and a second switch are connected in parallel to switch the output voltage so that the voltage value before the change is obtained. The smoothing circuit according to claim 1, further comprising a second parallel circuit capable of switching values.   When the output of the smoothing circuit is connected to one input of the comparison detection circuit, a fourth resistance element and a third switch are connected in parallel to control the voltage of the other input of the comparison detection circuit. The smoothing circuit according to claim 2, further comprising a third parallel circuit capable of switching a resistance value.   4. The resistance element of the first parallel circuit, the second parallel circuit, and the third parallel circuit of the smoothing circuit is a variable resistance element, and the capacitance element is a variable capacitance element. Smoothing circuit.   5. The smoothing circuit according to claim 4, further comprising a control unit configured to control the variable resistance elements and the variable capacitance elements of the first parallel circuit, the second parallel circuit, and the third parallel circuit.

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