JPH0229111A - Switched capacitor filter device - Google Patents

Abstract

PURPOSE:To reduce the deterioration in the attenuation characteristic of the filter by providing a switch sampling and holding the post-stage input to a connection section of a switched capacitor filter(SCF). CONSTITUTION:A signal including a signal component required for the final output and an undesired signal component is given to the SCF 4 through a switch 1. The input signal is sampled and held by the input of the SCF 4 the moment the switch 1 turned on the phase A is turned off and the SCF 4 attenuates the undesired signal component according to the attenuation characteristic. The processed signal is outputted from an output 7, inputted to the SCF 5 through a switch 2 and the SCF 5 attenuates the undesired signal component according to the attenuation characteristic similarly. Moreover, the signal processed similarly is outputted from the SCF 6. Thus, the SCF input of the post-stage at each cascade connection section of the SCFs 4-6 connected in cascade is sampled and held for a period not including any error in the SCF output of the pre-stage to reduce the deterioration in the attenuation characteristic.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a switched capacitor filter (hereinafter abbreviated as SCF) device used in signal processing devices such as modems and voice synthesizers.

BACKGROUND OF THE INVENTION In recent years, SCFs have come into use as integrated circuits for processing voice band signals have become more highly integrated and highly accurate.

A conventional SCF device will be described below.

Figure 2 is a configuration diagram of a conventional SCF device, and 11.12
．． 13 is an SCF having a second order, 14 is an output of 5CFII, 15 is an input of 5CF12, 16 is an output of 5CF13, and 17 is an input of 5CF14.

Figure 3 is a configuration diagram of the SCF with the above-mentioned second order, where 18, 21.23, 25.26 are switches that are turned on in the A phase, and 19, 20, 22.24°27 are switches that are turned on in the B phase. 28 to 35 are capacitors, and 36 and 37 are operational amplifiers (hereinafter abbreviated as operational amplifiers).

FIG. 4 is an output voltage waveform diagram of the SCF shown in FIG. 3, where 38 is a drive voltage waveform for turning on the A-phase switch, 39 is a drive voltage waveform for turning on a B-phase switch, and 40 is the actual output voltage waveform of the SCF shown in Figure 3, 4
The dashed line 1 is the ideal output voltage waveform of the SCF shown in FIG.

The operation of the SCF device configured as described above will be explained.

First, a signal containing signal components required for the final output and unnecessary signal components is input to 5CFII.

5CFII attenuates unnecessary signal components according to its attenuation versus frequency characteristics (hereinafter abbreviated as attenuation characteristics). The processed signal is outputted from output 14, and input 1 of 5CF12
Enter 5. The SCF 12 attenuates unnecessary signal components according to its attenuation characteristics. Output the processed signal 1
6 and input to input 17 of 5CF13. 5C
F13 attenuates unnecessary signal components according to its attenuation characteristics. The processed signal is output from 5CF13.

Problems to be Solved by the Invention However, in the conventional SCF configuration shown in FIG. 3, as shown in FIG. However, in reality, when the drive voltage waveform 39 for turning on the B-phase switch is applied,
This results in a difference of ΔV. For this reason, the damping characteristics of the SCF that had been predicted in advance deteriorate, resulting in a disadvantage that desired damping characteristics cannot be obtained.

As an example, if the output voltage V of a secondary SCF with a notch is B
When a driving voltage 50 is applied that turns on the phase switch,
FIG. 5 shows how much the attenuation characteristic changes by changing ΔV.

The Z function used is expressed by the following equation.

(1) In FIG. 5, the vertical axis represents the attenuation rate in decibels (dB). The horizontal axis represents the frequency normalized by the frequency fc of the drive voltage waveform for turning on the A-phase switch. In addition, 42 is the ideal attenuation characteristic of △V/V=O, and 43 is ΔV/
44 represents the attenuation characteristic when V=0.5%, and 44 represents the attenuation characteristic when ΔV/V=1%.

Looking at this, it can be seen that although the damping characteristic 44 has a slight difference of 8V/V=1%, the notch portion has undergone a large change and the characteristic has deteriorated.

The present invention solves the above-mentioned conventional problems, and aims to provide an SCF device that can significantly improve the attenuation characteristics of the SCF.

Means for Solving the Problems In order to achieve this object, the SCF device of the present invention has a configuration in which the cascade connection of the SCFs that are its constituent elements is provided with a switch that is turned on in the A phase.

According to the present invention, by providing the input section of the SCF with a switch that samples and holds the signal, deterioration of the attenuation characteristics can be reduced.

EXAMPLE Hereinafter, an example of the present invention will be described with reference to the drawings.

FIG. 1 shows a configuration diagram of an SCF device in an embodiment of the present invention. In FIG. 1, 1.2.3 is a switch that is turned on in the A phase. In addition, 4.5.6 is SCF
, 7 is the output of 5CF4, 8 is the input of 5CF5, 9 is 5C
The output of F5 and 10 are the inputs of 5CF6, which are the same as the configuration of the conventional example.

Next, the operation of the SCF device of this embodiment will be explained.

First, a signal containing a signal component required for the final output and an unnecessary signal component is inputted to the 5CF4 through the switch 1.

This input signal is sampled and held at the input of 5CF4 at the moment switch 1, which is turned on in the A phase, is turned off. 5CF
4 attenuates unnecessary signal components according to its attenuation characteristics. Output the processed signal from the output cuff and switch 2
Input to 5CF5 through. This input signal is sampled and held at the input of 5CF5 at the moment the switch 2, which is turned on in the A phase, is turned off. 5CF5 attenuates unnecessary signal components according to its attenuation characteristics. The processed signal is output from output 9 and input to 5CF6 through switch 3. This input signal is sampled and held at the input of 5CF6 at the moment the switch 3, which is turned on in the A phase, is turned off.

5CF6 attenuates unnecessary signal components according to its attenuation characteristics. The processed signal is output from 5CF6.

As described above, according to this embodiment, the cascade-connected SCFs
In each cascade connection of the SCF input of the subsequent stage, the SCF input of the previous stage
Deterioration of the attenuation characteristics can be reduced by sampling and holding the CF output during a period in which no error is included.

Note that in the above embodiment, the SCF is an SC having a second order.
Although F is used, it may be of primary or higher order. Also, in the configuration diagram, S
Although the CFs are only connected in cascade, they may be connected only in parallel or may be connected in a mixture of cascade and parallel connections. Further, although the switch for sample and hold is arranged at the connection part of the SCF, it may be provided directly in each SCF.

Effects of the Invention According to the present invention, by providing a switch for sample-holding the input of the subsequent stage at the connection part of the SCF, an excellent SC
This makes it possible to realize an F device.

[Brief explanation of the drawing]

Fig. 1 is a block diagram of an SCF device according to an embodiment of the present invention, Fig. 2 is a block diagram of a conventional SCF device, and Fig. 3 is a block diagram of an SCF device according to an embodiment of the present invention.
Figure 4 is a diagram showing the relationship between the SCF output voltage waveform and the switch drive voltage waveform that is turned on in the A phase and the switch drive voltage waveform that is turned on in the B phase used in the SCF. Figure 5 is a diagram showing the relationship between the SCF output voltage waveform and the switch drive voltage waveform that is turned on in the B phase. FIG. 7 is an attenuation characteristic diagram showing a change in the attenuation characteristic of the subsequent SCF with respect to the error ratio of the output waveform of the preceding SCF at the connection portion. 1.2.3...Switch turned on in A phase, 4゜5.6...SCF, 7...5CF4 output, 8...5CF5 input, 9...
Output of 5CF5, input of 10...5CF6. Name of agent: Patent attorney Shigetaka Awano and 1 other person

Claims (1)

[Claims] A switched capacitor filter device comprising a sample and hold switch at an input section of the switched capacitor filter.