SU1561199A1 - Synchronous filter - Google Patents

Abstract

This invention relates to a measurement technique. The purpose of the invention is to reduce switching noise. The synchronous filter contains an integrating circuit 1, an amplifier 2, switches 4 - 7, an inverter 10, a distributor 11 pulses and N parallel circuits, each of which consists of a capacitor 8 and a switch 9. The goal is achieved by introducing an inverting amplifier 3, which integrates on the condenser circuit 1 restores the inverted value of the charge accumulated in the previous period, which allows the spectral noise lines to be outside the passband of the filter. 3 il.

Description

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The invention relates to a measurement technique and can be used in frequency selection devices for electrical signals.

The purpose of the invention is to reduce switching noise.

FIG. 1 shows a structural electrical circuit of a synchronous filter; in fig. 2 - voltage agaors at the output of the distributor to impulse s; in fig. 3 - amplitude-frequency characteristics of the synchronous filter.

The synchronous filter contains an integrating circuit 1, an amplifier 2, an inverting amplifier 3, a first switch 4, an iteration switch 5, a third switch 6S a fourth switch 79 N parallel circuits, each of which contains a capacitor 8 and a switch 9, an inverter 10 and a distributor 11 pulses ,

The synchronous function works as follows.

Consider first the work filter15611994

i is equal to the full cycle of switching keys. The role of the adder is played by the capacitor of the integrating circuit 1. The frequency response of the recirculator is a comb, described by the relation

A (w)

one

ten

/ 1 -2/3 coswT + / 3

15

20

where T is the time delay;

p is a coefficient depending on the accumulation value per cycle.

Due to the non-identical parameters of the (electronic) switches 9, as well as the effect of the control pulses, the capacitors 8 are randomly recharged. Switching noise appears, the period of which is equal to the full switching cycle, and the noise spectral lines (Fig. 2a) are located exactly at the resonant frequencies of the filter. The addir, when there is no inverting yen-25, is conveniently added to the useful signal 3. The keys 91–9 work alternately and separately in time (Fig. E-d). Simultaneously with otkryve1

one of the keys, for example 9

R

open the third and fourth keys 6 and 7 (Fig. 3a). The capacitor of the input Integrating circuit 1 through the amplifier 2, operating in repeater mode, is connected to the capacitor 8, and the voltage across it quickly becomes equal to the voltage on this capacitor. Thereafter, the third and fourth 6 and 7 are closed, and the first and second keys 4 and 5 are opened and remain open until the end of the on state of the key 9.

During this time, integrating circuit 1 accumulates the input voltage. After locking the key 9.J, the key 9 is opened, as well as the third and fourth keys 6 and 7, the process is repeated. If the period of the complete switching cycle of keys 9 - 9 coincides with the period of the input signal, then the recovery process on the capacitor of the previously accumulated voltage coincides in phase with the input signal and its effective accumulation occurs. If there are a large number of parallel branches, then the specified circuit is equivalent to a recirculator, which is an adder covered by feedback through a delay line. Here is the delay

thirty

signal switching noise significantly reduces the dynamic range of the known filter.

The operation of the proposed filter is no different from the work of the known one, except that the inverted value of the charge accumulated in the previous period is restored on the capacitor of the integrating circuit. An inverting 35 amplifier 3 is introduced. At the same time, at the switching frequency of the keys 9, there will no longer be an effective accumulation, since in each clock cycle the signal is subtracted from the previously accumulated one. This is also true for all frequencies that are multiples of the switching frequency. Efficient accumulation occurs, in particular, for a signal with a frequency equal to half the switching frequency. This is confirmed by the fact that the frequency response of the recirculator in the presence of inversion in the feedback circuit is described by the relation

40

45

50

A (w)

one

 2 / jcoswT +02

55

It is shifted upward along the frequency axis by the value of w / 2 (Fig. 26). When the switching conditions do not change, the spectral noise lines remain in place and are outside the passband of the filter. Thanks to this, the switching noise is suppressed by the

A (w)

one

ten

/ 1 -2/3 coswT + / 3

five

0

where T is the time delay;

p is a coefficient depending on the accumulation value per cycle.

Due to the non-identical parameters of the (electronic) switches 9, as well as the effect of the control pulses, the capacitors 8 are randomly recharged. Switching noise appears, the period of which is equal to the full switching cycle, and the noise spectral lines (Fig. 2a) are located exactly at the resonant frequencies of the filter. Additively add a useful sig

signal switching noise significantly reduces the dynamic range of the known filter.

The operation of the proposed filter is no different from that of the known, except that the inverted value of the charge accumulated in the previous period is restored on the capacitor of the integrating circuit. An inverting amplifier 3 is introduced. At the same time, at the switching frequency of the keys 9, there will no longer be an effective accumulation, since in each clock cycle the signal is subtracted from the previously accumulated one. This also applies to all frequencies that are multiples of the switching frequency. Efficient accumulation occurs, in particular, for a signal with a frequency equal to half the switching frequency. This is confirmed by the fact that the frequency response of the recirculator in the presence of inversion in the feedback circuit is described by the relation

50

A (w)

one

 2 / jcoswT +02

It is shifted upward along the frequency axis by the value of w / 2 (Fig. 26). Because the switching conditions do not change, the spectral noise lines remain in place and are outside the filter bandwidth. Due to this, the switching noise is suppressed by the user.

filter and in comparison with the known synchronous filters, their effect is reduced by several orders of magnitude. With regard to the requirements for a constant, the time of the integrating circuit 1, then for the normal operation of the filter it is enough that it is much longer than the switching cycle time T, In this case the filter will be narrowband.

Claims (1)

Invention Formula A synchronous filter containing a series-connected integrating RC circuit, a first switch, an amplifier, and a second switch, a third and fourth switch N of parallel circuits, each of which consists of a series-connected capacitor and a switch, the first terminals of the capacitors being combined and BUT № „ ajo 2 } ". {". I 2 61199 ten the second filter is connected to the common bus; the control inputs of the keys of the N parallel circuits are connected to the corresponding outputs of the pulse distributor, the (N + 1) -th output of which is connected to the control inputs of the third and fourth keys, and the control inputs of the first and second keys are via an inverter, the amplifier input is connected via the third switch to the output of the second switch, and the input of the fourth switch is connected to the output of the integrating RC circuit, the input of which is the input of a synchronous filter that distinguishes so that, in order to reduce switching noise, between the output of the fourth key and the input 20 the house of the second key is switched on an inverting amplifier. 15 Jw 4u ( (l) T T i 2 B Sh0 W D il P O I P P I P P j Ta Schppppppppppg I I I I t -n- one I Q P . FIG. five Q P t P