RU2296418C1 - Broadband multichannel piezoelectric filtering device - Google Patents

Abstract

FIELD: radio electronics; signal processing radio receivers and instrumentation engineering.

SUBSTANCE: proposed filtering device of "1 input-N + 1 outputs" multichannel design has algebraic adder built around operational amplifier 1 provided with resistive negative feedback 2 and resistors 3. 4 connected to its inverting and noninverting inputs, resistor 5 connected between input of operational amplifier 1 and common line, piezoelectric resonators 6, 7 whose first leads are connected to input potential terminal of device and second ones, to inverting inputs of operational amplifiers 10, 11 through resistors 8, 9 with resistive negative feedbacks 12, 13 applied to each of them; outputs of operational amplifiers 10, 11 are connected to second leads of resistors 3, 4, respectively. Newly introduced is oscillatory circuit 14 set up of series-connected LC elements 15, 16 which is connected to output of operational amplifier 1, second lead of LC circuit being connected to output potential terminal of device and through resistor 17, to common bus.

EFFECT: extended passband of proposed multichannel filtering device.

2 cl, 2 dwg

Description

The proposed device relates to electronics and can be used in radio receivers when processing signals, as well as in measuring equipment as a multi-channel filter.

A number of filtering devices are known, in particular, one of them is shown in FIG. 1 [1]. The device contains an algebraic adder made on a differential operational amplifier with resistive negative feedback, the output of which is the output of the device, while the first resistor is connected to the inverting input of the operational amplifier, the second output of which is the first input of the adder, the second and third are connected to the non-inverting input of the operational amplifier resistors, the second terminal of the second resistor is the second input of the adder, the second terminal of the third resistor is connected to a common bus In addition, the device contains a second and third inverting operational amplifiers with resistive negative feedbacks, the outputs of which are connected to the first and second inputs of the said adder, respectively, between the input of the device and the input of the second operational amplifier, as well as between the input of the device and the input of the third operational amplifier or more two-terminal devices consisting of a piezoresonator and a resistor connected in series.

This device allows you to implement a multi-channel filter with fairly high requirements for attenuation in the delay band and dynamic range. It is the closest to the proposed device and is selected as a prototype. The disadvantage of this device is that it allows you to implement only narrow-band filters and does not provide separation of channels by output (it has only one common potential output terminal).

The objective of the invention is the expansion of the functionality of the device, in particular for the construction of broadband piezoelectric filters in multi-channel design, having the structure of "one input - N + 1 output.

The problem is solved in that in a broadband multichannel piezoelectric filter device containing an algebraic adder, made on the first operational amplifier with resistive negative feedback, with the first and second resistors connected to its inverting and non-inverting inputs, a third resistor is connected between the non-inverting input of the first operational amplifier and a common bus, the first and second piezoresonators, the first conclusions of which are connected to the input potential terminal of the device and the second outputs of the piezoresonators are connected through the fourth and fifth resistors to the inputs of the second and third inverting operational amplifiers, each of which is covered by resistive negative feedback, while the outputs of the second and third operational amplifiers are connected to the second outputs of the first and second resistors, respectively, an oscillatory circuit consisting of an inductor and a capacitor connected to the output of the first operational amplifier, the second output in series This circuit is connected to the potential output terminal of the device and through the sixth resistor with a common bus.

In addition, according to the subject of the invention, N channels are additionally introduced into the device, where N = 1, 2, 3 ..., in structure identical to the main device, while the first conclusions of the first and second resonators of the additionally introduced channels are connected to the input potential terminal of the device and the second conclusions of the serial circuits in each channel are connected to the additionally introduced output potential terminals of the device.

The essence of the invention consists in the construction of a broadband filtering device, allowing the combination at the input of N + 1 - independent channels and having N + 1 separate outputs.

Figure 2 shows the electrical circuit of the proposed device. The device consists of an algebraic adder made on an operational amplifier 1 with resistive negative feedback 2, with resistors 3 and 4 connected to its inverting and non-inverting inputs, a resistor 5 is connected between the non-inverting input of the operational amplifier 1 and a common bus, piezoresonators 6 and 7, the first the terminals of which are connected to the input potential terminal of the device, and the second terminals of the piezoresonators 6 and 7 are connected through resistors 8 and 9 to the inputs of the inverting operational amplifiers 10 and 11, each of which of the outputs is covered by resistive negative feedback 12, 13, respectively, while the outputs of the operational amplifiers 10, 11 are connected to the second terminals of the resistors 3 and 4, respectively, to the output of the operational amplifier 1 is connected a series oscillatory circuit 14, consisting of an inductor 15 and a capacitor 16, the second the output of the serial circuit 14 is connected to the output potential terminal of the device and through a resistor 17 with a common bus.

In addition, the device is made multi-channel, containing additional N channels, in structure identical to the main device, while the first conclusions of the resonators 6 and 7 of the additionally introduced channels are connected to the input potential terminal of the device, and the second conclusions of the serial circuits 14 in each additional channel are connected to the additionally introduced potential output terminals of the device.

The device operates as follows. Part of the device circuit from the input (the first conclusions of the piezoresonators 6 and 7) to the output of the algebraic adder (output of the operational amplifier 1) is a band-pass filter, the transfer function of which can be represented as:

where Y ₁ and Y ₂ - the conductivity of the piezoresonators 6 and 7;

g _H is the load conductivity determined by resistors 8 and 9 (we assume that resistors 8 and 9 are equal in magnitude).

With the appropriate choice of the parameters of the piezoresonators, this circuit implements a band-pass filter whose bandwidth does not exceed the double frequency gap of the piezoresonator ΔF = f _p -f _q (here f _p is the frequency of the parallel resonance, f _q is the frequency of the serial resonance of the piezoelectric resonator) [2].

Connection to the output of this circuit circuit formed by a sequential oscillatory circuit 14 and a resistor 17, leads to the resulting transfer function of the form:

,

,

where L, C is the inductance and capacitance of the series circuit 14,

R is the resistance of the resistor 17.

The solution of the equation p ² LC + pRC + 1 = 0, shows that the resulting transfer function has an additional complex pole

,

,

- резонансная частота контура 14.Where

is the resonant frequency of the circuit 14.

It can be shown that the real parts of the poles of the transfer function affect the filter bandwidth. The wider the bandpass filter you want to get, the greater the absolute value should be the real part of the complex pole of the transfer function. In this case, the real part of the pole is determined by the ratio of R to L and can vary within wide enough limits.

In [3] it was shown that solving the equation Y ₁ + g _H = 0 leads to an expression of the form:

,

,

where L _q is the dynamic inductance of the piezoresonator;

w ₁ is the frequency of the series resonance of the piezoresonator;

With ₀ is the static capacity of the piezoresonator;

w ₀ is the average frequency of the filter;

p is the complex frequency.

This ratio makes it possible to evaluate the feasibility of implementing the pole of the transfer function when using a piezoelectric resonator with available real parameters (L _q , C _q , C ₀ , ΔF).

As a rule (see, for example, [4]), the transfer functions of third-order strip chains (with respect to p ² ) contain two pairs of complex conjugate poles with real parts σ ₁ and σ ₂ and one pair of poles with the real part σ ₀ , and σ ₁ ≈σ ₂ <σ ₀ . Therefore, it is possible to implement the first two pairs of poles on piezoresonators 6 and 7 included in the first filter link, and the second pair of poles can be implemented by the second link, consisting of a series LC circuit 14 and resistor 17, which allows to obtain 3-4 times wider passband compared to the prototype filter.

Thus, in the proposed device, the introduction of an additional cascade-decoupled LC link makes it possible to obtain wider bandwidths in a relatively simple way. Connecting additional filters identical in structure, which allow parallel connection at the input, since their load resistance (determined by the conductivity g _H ) almost always significantly exceeds the internal resistance of the signal source, and therefore, the proposed device implements a multi-channel filtering device in accordance with the task - the expansion of functional of opportunities.

Information sources

1. RF patent No. 2171009, cl. 7 H 03 H 9/54, 7/01. Active piezoelectric filter, publ. 07/20/2001, BI No. 20.

2. Velikin Y.I., Helmont Z.Ya., Zelyakh, E.V. "Piezoelectric filters" - M., Communication, 1966.

3. Bolotyuk A.A. Active quartz filters on operational amplifiers, - Radio instrument making and microelectronics. Issue 4, 1975.

4. Zaal R. Handbook for the calculation of filters, - M .: Radio and communication, 1983.

Claims (2)

1. A broadband multichannel piezoelectric filter device containing an algebraic adder made on the first operational amplifier with resistive negative feedback, with first and second resistors connected to its inverting and non-inverting inputs, the third resistor is connected between the non-inverting input of the first operational amplifier and the common bus, the first and a second piezoresonator, the first conclusions of which are connected to the input potential terminal of the device, and the second conclusions of the piezoresonator in through the fourth and fifth resistors are connected to the inputs of the second and third inverting operational amplifiers, each of which is covered by resistive negative feedback, while the outputs of the second and third operational amplifiers are connected to the second terminals of the first and second resistors, respectively, characterized in that the output of the first operational amplifier connected to a serial oscillatory circuit, consisting of an inductor and a capacitor, the second output of the serial circuit is connected to the output the potential terminal of the device and through the sixth resistor with a common bus. 2. The device according to claim 1, characterized in that an additional N channels are introduced into the circuit, where N = 1, 2, 3 ..., in structure identical to the device according to claim 1, wherein the first conclusions of the first and second resonators are additionally the input channels are connected to the input potential terminal of the device, and the second outputs of the serial circuits in each channel are connected to the additional input potential terminals of the device.

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