CS215728B1 - Dual capacitor circuitry - Google Patents

Abstract

The invention relates to the field of low-power communication electrical engineering. The invention solves the connection of a double Integrator with a minimized number of active and passive elements. The essence of the invention is the use of the frequency dependence of the voltage gain of a real operational amplifier with internal or external correction of the frequency characteristic, which in most common operational amplifiers corresponds to the transfer function of an ideal Integrator. The connection is characterized by the fact that the first input terminal is connected both to the input of the operational amplifier and, through a capacitor, to the output of the operational amplifier. The second input terminal is connected to the common (ground terminal) of the operational amplifier. The invention can be used especially in low-power electrical engineering for the implementation of electrical frequency filters with a crossbar structure and one common terminal of a double capacitor, for example in Cauer filters of the low-pass type. Fig. 2 of the application shows an alternative diagram characterizing the connection of a double capacitor.

Description

The invention relates to the connection of a double capacitor e with a minimized number of active and passive circuit elements. Frequency dependence of voltage amplification of real operational amplifier is used in the connection.

The modern synthesis of electric frequency filters uses an active function block with input admittance

Y (p)

P ² · D, where Y (p) is the frequency-dependent admittance, p is the complex frequency, and D is the value of the double capacitance, which is called the frequency independent negative resistor, or more preferably the double capacitance. The prior art dual capacitor circuits utilize relatively complex circuitry with mutators or operational amplifiers and a network of passive RC elements. A relatively large number of active elements are required for the realization of the double capacitor, the use of which complicates the resulting connection of the electric frequency filter with the double capacitors. There is also a growing demand for the active filter and the noise level.

The aforementioned difficulties are solved by the dual capacitor circuit according to the invention, characterized in that the first input terminal is connected both to the non-inverting input of the real frequency compensated opamp, and through the capacitor to the real frequency compensated opamp output. The second input terminal is connected to the common (ground) terminal of the real frequency compensated operational amplifier and to the inverting input of the real frequency compensated operational amplifier.

Compared to the prior art double capacitor circuitry, the dual capacitor circuitry of the invention has the advantage of simplicity of wiring, its low cost, and the fact that conventional integrated operational amplifiers are used for its implementation.

The proposed wiring shows impedance r ~ - - τ,, 1 on the input terminals. ^A O ^{, W >}

Z (p) - R _at * p _C + ---,

P. C where R _y is the operational amplifier output resistance, Αθ is the DC amplifier of the operational amplifier, Q3 _zl is the frequency of the frequency amplification frequency response of the operational amplifier with standard frequency correction, p is the complex frequency the operational amplifier terminal. The substitute model of such realized double capacitor consists of the series ideal ideal double capacitor with impedance _z , (p) = p ² . C with the double capacity value

C

D = -: ^A o- ° \ laz of parasitic elements - resistor R _y and capacitor C. In practical design of electric frequency filters, the influence of parasitic elements can in most cases be neglected or included in the filter calculation. Compared to other frequency filter circuits used with dual capacitors implemented in other ways, the circuitry according to the invention is much simpler in terms of the number of active and passive elements used and makes full use of mass-produced monolithic integrated operational amplifiers.

215 728

Fig. 1 shows a double capacitor according to the invention, Fig. 2 shows a spare null model of the double capacitor according to the invention, Fig. 3 shows a spare model of the double capacitor according to the invention, including parasitic elements. of the third order dual capacitor according to the invention.

In a particular embodiment of the double capacitor, the first input terminal 1 is connected both to the non-inverting input 2 of the real frequency compensated operational amplifier, and through the capacitor 4 to the output £ of the real frequency compensated operational amplifier 3. the operational amplifier £.

The function of the circuit follows from the mathematical description of the substitute null model of the connection according to Fig. 2. Null model, the admittance 8 of the value

A real operational amplifier is simulated by a resistor respekt respecting the non-zero value of the output resistance R _γ . The circuit uses frequency dependence of amplification of real operational amplifier with internal or external frequency correction, which can be described in relation to most common operational amplifiers

A _q , cozl

4 _µ (p, = -,

P

Ke A _u (p) is the value of the frequency-dependent voltage transfer of the operational amplifier, which corresponds to the transfer function of the ideal integrator. The shortened reduced admittance matrix of FIG.

has the form:

pC + Y _o (p) + G _{in the} input impedance of the admittance matrix

2 pC-pC

-pC-Y ₀ (p) on the terminals 11 'of the connection according to Fig. 2 is expressed from algebraic supplements as

Z, vst (p) = pc. C

Thus, between the input terminals 1 and 6, the circuit shown in FIG. 1 shows an impedance with the impedance of double capacity.

The double capacitor circuit according to the invention can be used, in particular, for the implementation of electric frequency filters with a partition structure and one common double capacitor terminal. A preferred feature of the circuitry is the minimized number of circuit elements. The double capacitor circuit according to the invention can also be used in more complex wiring of low-pass electric frequency filters, such as Bauer filters. The wiring can be easily realized in the form of a hybrid integrated circuit.

Claims (1)

Dual fcapaeitor connection, characterized in that the first input terminal (1) is connected both to the non-inverting input (2) of the real frequency compensated operational amplifier (3) and to the output (5) of the real frequency compensated operational amplifier (3) ), the second input terminal (6) is connected to a common (ground terminal) of the operational amplifier (3) and to the inverting input (8) of the real frequency compensated operational amplifier (3).