RU2818305C1 - Discrete-analogue filter on switched capacitors - Google Patents

Abstract

FIELD: radio engineering.

SUBSTANCE: invention relates to radio engineering and can be used to select given signal spectra, for example, during their analogue-to-digital conversions. Discrete-analogue filter on switched capacitors additionally contains multidifferential operational amplifier (15) with two input ports. Inverting input (16) of the first port of multidifferential operational amplifier (15) is connected to its output. Non-inverting input (17) of the first port of multidifferential operational amplifier (15) is connected to output (2) of the device. Inverting input (18) of the second port of multidifferential operational amplifier (15) is connected to a common power supply bus. Non-inverting input (19) of the second port of multidifferential operational amplifier (15) is connected to input (1) of the device. Output of multidifferential operational amplifier (15) is connected to the input of voltage follower (14) through series-connected first (7) and second (8) electronic switches. Common unit of first (7) and second (8) series-connected electronic switches is connected to common bus of power sources through second (11) frequency-setting capacitor. Input of voltage follower (14) is connected to the common bus of the power sources through third (12) frequency-setting capacitor. Output of voltage follower (14) is connected to inverting (4) input of differential operational amplifier (3) through series-connected third (9) and fourth (10) electronic switches. Common unit of series-connected third (9) and fourth (10) electronic switches is connected to common bus of power sources through fourth (13) frequency-setting capacitor.

EFFECT: high quality factor of the pole, ensuring independence of the transfer coefficient of the discrete-analogue filter at zero frequency from the capacitance values of frequency-setting capacitors, high manufacturability of the DAF with its microelectronic design.

1 cl, 7 dwg

Description

The present invention relates to the field of radio engineering and can be used to isolate specified spectra of signals, for example, during their analog-to-digital conversions.

Despite the fact that the digital transformation of industrial production makes extensive use of digital analog signal processing methods, they are redundant in some cases. As a consequence, discrete-analog processing, which combines the main advantages of analog-digital methods, is very promising. Thus, discrete-analog filters on switched capacitors (DSF), produced by dozens of leading microelectronic companies in the world, incl. Texas Instruments (USA), Maxim (USA), CYPRESS (USA), Analog Devices (USA), etc., provide a significant gain (in comparison with classic digital and analog filters) in size, cost, accuracy, functionality and are an effective means construction of frequency selection circuits and processing of analog signals in science and technology.

Discrete-analog switched capacitor filters and their practical applications have become the subject of intense intellectual property protection in almost every country in the world over the past 30 years [1-86]. The most promising DAF solutions [1-86] are patented by companies in the USA, Japan, France, Taiwan, China, Germany, Great Britain, Italy, etc.

The closest prototype of the proposed device is a discrete analog low-pass filter (Fig. 1), described in patent RU 2801744C1. It contains (Fig. 1) input 1 and output 2 of the device, a differential operational amplifier 3 with an inverting 4 input and a non-inverting 5 input connected to a common power supply bus, the output of the differential operational amplifier 3 is connected to the output 2 of the device, the first 6 frequency-setting capacitor, connected between the output of the differential operational amplifier 3 and its inverting 4 input, the first 7, second 8, third 9 and fourth 10 series-connected electronic switches, the second 11, third 12 and fourth 13 frequency-setting capacitors, voltage follower 14.

A significant drawback of the known discrete-analog filter on switched capacitors (Fig. 1) is that three of the four capacitors do not have terminals connected to the common power supply bus. In this case, the transmission coefficient of the DAF prototype depends on the capacitances of the frequency-setting capacitors.

The main objective of the present invention is to create a discrete analog filter on switched capacitors, in which most of the frequency-setting capacitors are connected to a common bus with one output, as well as to implement a higher pole quality factor, which is necessary for constructing high-order filters. In this case, the transmission coefficient of the proposed DAF at zero frequency is always equal to minus one and does not depend on the capacitance values of the frequency-setting capacitors. This advantage is achieved by introducing Fig. 1 new connections between elements in accordance with the claims. This circuit design improves the manufacturability of the DAF with its microelectronic design.

The task is achieved by the fact that in the discrete-analog filter on switchable capacitors Fig. 1, containing input 1 and output 2 of the device, a differential operational amplifier 3 with an inverting 4 input and a non-inverting 5 input connected to a common power supply bus, the output of the differential operational amplifier 3 is connected to the output 2 of the device, the first 6 frequency-setting capacitor connected between the output of the differential operational amplifier 3 and its inverting 4 input, first 7, second 8, third 9 and fourth 10 series-connected electronic switches, second 11, third 12 and fourth 13 frequency-setting capacitors, voltage follower 14, new elements and connections are provided - a multi-differential one is introduced into the circuit operational amplifier 15 with two input ports, and the inverting input 16 of the first port is connected to the output of the multi-differential operational amplifier 15, the non-inverting input 17 of the first port is connected to the output 2 of the device, the inverting input 18 of the second port is connected to the common power supply bus, and the non-inverting input 19 of the second port is connected to input 1 of the device, the output of the multi-differential operational amplifier 15 is connected to the input of the voltage follower 14 through the first 7 and second 8 electronic switches connected in series, the common node of the first 7 and second 8 series-connected electronic keys is connected to a common power supply bus through the second 11 frequency-setting capacitor, the input of the voltage follower 14 is connected to the common bus of power supplies through the third 12 frequency-setting capacitor, the output of the voltage follower 14 is connected to the inverting 4 input of the differential operational amplifier 3 through the third 9 and fourth 10 electronic switches connected in series, and the common node of the third 9 and 10 connected in series The fourth 10 electronic keys are connected to the common power supply bus through the fourth 13 frequency-setting capacitor.

In the drawing FIG. Figure 1 shows the circuit of a discrete-analog filter on switched capacitors - a prototype.

In the drawing FIG. Figure 2 shows a diagram of the proposed discrete-analog filter on switched capacitors in accordance with the claims of the invention.

In the drawing FIG. Figure 3 shows a diagram of the proposed DAF for modeling in the Micro-Cap environment.

In the drawing FIG. Figure 4 shows the sequences of pulses that control the DAF electronic keys.

In the drawing FIG. Figure 5 shows the results of modeling the DAF circuit of Fig. 3 in a Micro-Cap environment at an input signal frequency of 1591 Hz, coinciding with the filter pole frequency.

In the drawing FIG. 6 shows the results of modeling the circuit of Fig. 3 at a very low input frequency (15.91 Hz). From this graph it follows that the transmission coefficient of the proposed filter in the very low frequency range is close to unity.

In the drawing FIG. Figure 7 shows the results of modeling the circuit of Fig. 3 at high input signal frequency (159100 Hz). From this graph it follows that the transmission coefficient of the proposed filter in the high frequency range takes on very small values.

Thus, the graphs of Fig. 6 and fig. 7 show that the inventive device has the properties of a low-pass filter.

The peculiarity of the proposed DAF circuit is that at a pole frequency of 1591 Hz it has a transmission coefficient equal to minus one, which does not depend on the spread of parameters of other elements of the circuit. In addition, when implementing high quality factors of the pole, a smaller ratio of the capacitances of the frequency-setting capacitors is required here.

Discrete-analog filter on switched capacitors Fig. 2 contains input 1 and output 2 of the device, a differential operational amplifier 3 with an inverting 4 input and a non-inverting 5 input connected to a common power supply bus, the output of the differential operational amplifier 3 is connected to the output 2 of the device, the first 6 frequency-setting capacitor is connected between the output of the differential operational amplifier 3 and its inverting 4 input, the first 7, second 8, third 9 and fourth 10 series-connected electronic switches, the second 11, third 12 and fourth 13 frequency-setting capacitors, voltage follower 14. The circuit includes a multi-differential operational amplifier 15 with two input ports , and the inverting input 16 of the first port is connected to the output of the multi-differential operational amplifier 15, the non-inverting input 17 of the first port is connected to the output 2 of the device, the inverting input 18 of the second port is connected to the common power supply bus, and the non-inverting input 19 of the second port is connected to the input 1 of the device, the output of the multi-differential operational amplifier 15 is connected to the input of the voltage follower 14 through the first 7 and second 8 electronic switches connected in series, the common node of the first 7 and second 8 series-connected electronic keys is connected to the common power supply bus through the second 11 frequency-setting capacitor, the input of the voltage follower 14 is connected with a common power supply bus through the third 12 frequency-setting capacitor, the output of the voltage follower 14 is connected to the inverting 4 input of the differential operational amplifier 3 through the third 9 and fourth 10 electronic switches connected in series, and the common node of the series-connected third 9 and fourth 10 electronic keys is connected to the common power supply bus through the fourth 13 frequency-setting capacitor.

Let us consider the operation of the proposed discrete-analog filter in the drawing of Fig. 2.

With sequential and periodic closure of the first 7, second 8, third 9 and fourth 10 electronic keys, as well as at the frequency of switching electronic keys much higher than the pole frequency second-order link, as a result of mathematical analysis of the circuit of Fig. 2 it can be shown that this circuit implements the transfer function of a second-order low-pass filter

, (1)

the main parameters of which are found using the following formulas:

- low-pass filter transmission coefficient at zero frequency

(2)

- low-pass filter transmission coefficient at the pole frequency

(3)

- pole frequency

(4)

- pole attenuation

(5)

In formula (4) - switching frequency of electronic keys, and - their switching period, C ₆ , C ₁₁ , C ₁₂ and C ₁₃ - the capacitance of the first 6, second 11, third 12 and fourth 13 frequency-setting capacitors, respectively.

Compared to the prototype (Fig. 1), in the proposed circuit three frequency-setting capacitors 11, 12 and 13 are connected to a common bus. This increases the manufacturability of microelectronic DAPs.

The performance of the proposed circuit is confirmed by its simulation in the Micro-Cap program. In fig. 3 shows a diagram for simulation, and FIG. 4 - sequences of pulses controlling the first 7, second 8, third 9 and fourth 10 electronic keys.

In the drawing FIG. 5 shows the response of the circuit of FIG. 3 (its output voltage v(Out_1)) to the input sinusoidal signal v(In) with an amplitude of 1V and a frequency of 1125 Hz, which, with the parameters of the elements indicated in the diagram of Fig. 3 and the switching frequency of electronic keys is 1 MHz (their period is 1 μs) equal to the pole frequency , implemented by the circuit. In accordance with formula (3), at this frequency with the selected parameters of the elements, the transmission coefficient of the DAF is equal to . Numerical values if necessary may take other (smaller) values.

In the drawing FIG. 5 also shows (on an enlarged scale) a graph of the output signal of the DAF of FIG. 3, which is “stepwise” in nature. The stepwise nature of the DAF output signal corresponds to the physical processes of signal conversion in filters of the class under consideration.

In the drawings, Fig. 6 and Fig. Figure 7 shows the results of modeling the proposed DAF in the range of very low (100 times lower than the pole frequency, Fig. 6) and high (100 times higher than the pole frequency, Fig. 7) frequencies (compared to the pole frequency (4)). From these graphs, as well as Fig. 5, it follows that the device in question has the properties of a low-pass filter - it has a transmission coefficient close to unity at very low frequencies ( according to formula (2)) and a transmission coefficient close to zero at higher frequencies.

Thus, the proposed discrete analog filter has significant advantages in comparison with the DAF prototype. In it, the second 11, third 12 and fourth 13 capacitors are connected with one terminal to a common power supply bus, and the low-pass filter transmission coefficient at zero frequency M ₀ is equal to minus one and does not depend on other frequency-setting elements of the circuit.

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Claims (1)

Discrete-analog filter on switched capacitors, containing the input (1) and output (2) of the device, a differential operational amplifier (3) with an inverting (4) input and a non-inverting (5) input connected to a common power supply bus, the output of a differential operational amplifier (3) is connected to the output (2) of the device, the first (6) frequency-setting capacitor connected between the output of the differential operational amplifier (3) and its inverting (4) input, the first (7), second (8), third (9) and fourth (10) series-connected electronic switches, second (11), third (12) and fourth (13) frequency-setting capacitors, voltage follower (14), characterized in that a multi-differential operational amplifier (15) with two input ports is included in the circuit, wherein the inverting input (16) of the first port is connected to the output of the multi-differential operational amplifier (15), the non-inverting input (17) of the first port is connected to the output (2) of the device, the inverting input (18) of the second port is connected to the common power supply bus, and the non-inverting input (19) of the second port is connected to the input (1) of the device, the output of the multi-differential operational amplifier (15) is connected to the input of the voltage follower (14) through the first (7) and second (8) electronic keys connected in series, the common node of the first (7) and the second (8) series-connected electronic switches are connected to the common bus of power supplies through the second (11) frequency-setting capacitor, the input of the voltage follower (14) is connected to the common bus of power supplies through the third (12) frequency-setting capacitor, the output of the voltage follower (14) is connected to inverting (4) input of the differential operational amplifier (3) through the third (9) and fourth (10) electronic switches connected in series, and the common node of the series-connected third (9) and fourth (10) electronic keys is connected to the common power supply bus through the fourth (13) frequency-setting capacitor.