JP2573080Y2 - All-pass filter - Google Patents

Description

[Detailed description of the invention]

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an all-pass filter having a stable amplitude characteristic even when a group delay characteristic is varied.

[0002]

2. Description of the Related Art FIG. 5 shows an example of a conventional first-order all-pass filter, which comprises a variable conductance amplifier _A01 and a capacitor _C01.
And an adder 11 comprising a multi-input type operational amplifier A ₀₂ to which the output is supplied. The input terminal 1 is connected to the non-inverting input terminal of the variable conductance amplifier A ₀₁ and the operational amplifier A ₀₂ . The operational amplifier _A02 is connected to the inverting input terminal, and is a self-negative feedback type. Thus, it is constituted by the primary low-pass filter and the adder.

[0003]

FIG. 4 shows the group delay characteristic and the amplitude characteristic of the first-order all-pass filter in FIG. 5, in which the horizontal axis represents frequency, and the vertical axis represents attenuation and delay time. is there. When supplying operating current to the variable conductance amplifier A _01, the characteristic curve of the delay time at a frequency of 1 MH _Z 1b
To 2b. Accordingly, there is a disadvantage that the characteristic curve of the amplitude characteristic fluctuates in the range of 1a to 2a (about 0.2 mdB). When the amplitude characteristic fluctuates, the output level fluctuates, and it is extremely difficult to handle such a filter in combination with another filter to obtain a predetermined filter characteristic.

It is an object of the present invention to provide a first-order all-pass type in which the amplitude characteristic is kept constant even if the group delay characteristic is varied.
It provides a filter.

[0005]

The all-pass filter according to the present invention comprises an integrator comprising a variable conductance amplifier and a capacitor, and an operational amplifier to which the output of the integrator is supplied, and an input terminal of the variable conductance amplifier. Connected to a non-inverting input terminal and an inverting input terminal of the operational amplifier,
An output terminal of the operational amplifier is connected to an inverting input terminal of the variable conductance amplifier and another inverting input terminal of the operational amplifier.

[0006]

The all-pass filter according to the present invention provides a group delay characteristic by negatively feeding back the output to an integrator comprising a variable conductance amplifier and a capacitor and an adder comprising an operational amplifier to which the output of the integrator is supplied. Is varied, the amplitude characteristics are stabilized.

[0007]

DETAILED DESCRIPTION FIG. 1 shows one embodiment of an all-pass filter of the present invention, a first order all-pass filter, a variable conductance amplifier A ₁ and the integrator 3 comprising a capacitor C _1, the multi-input type and an adder 4 which consists of an operational amplifier a ₂ in. The operational amplifier A ₂ is self
Negative feedback type. Input terminal 1 of the filter is connected to the non-inverting input terminal of the variable conductance amplifier A ₁ to the inverting input terminal of the operational amplifier A _2, an output terminal of the integrator 3 is connected to the non-inverting input terminal of the operational amplifier A _2, An output terminal of the operational amplifier a ₂ is connected to the output terminal 2 is connected to the inverting input terminal of the variable conductance amplifier a _1, and,
It is connected to the other inverting input terminal of the operational amplifier A _2.
Negative feedback circuit is constructed by connecting to other inverting input terminal.
It is. Also, other non-inverting input terminal of the operational amplifier A ₂ is grounded. Figure 2 shows another embodiment of the all-pass filter of the present invention, in this embodiment, the output terminal of the integrator 3 is connected to two non-inverting input terminal of the operational amplifier A ₂ of the multi-input type The other connections are the same as in FIG.

The all-pass filter of the present invention can be represented by a block diagram as shown in FIG. The input voltage is V ₁ , the output voltage is V _2, and the transfer function of the integrator 3 is P / s (where s is jω, P is equal to gm / C, and gm is the transconductance of the integrator 3; When the integral capacity.), output voltage V _1, V ₂ can be expressed by the following equation. V ₂ = A · [P / s (V ₁ −V ₂ ) −V ₁ −V ₂ ] (1) (where A is a coefficient representing the gain of the operational amplifier)
Equation (1) is written as the following equation. V ₂ (1 / A + P / s + 1) = V ₁ (P / s-1) (2) Accordingly, when the transfer function T (s) is obtained from the equation (2), it is expressed as the following equation. You. _{T (s) = V 2 /} V 1 = (P / s-1) / (P / s + P / s + 1) = (P-s) / [P + s (1 + 1 / A) ] ............ (3) then In the equation (3), if the coefficient A is infinite, the transfer function T (s) is expressed as: T (s) = (P−s) / (P + s) (4) .

The transfer function T (jω) in the equation (4) can be expressed by the following equation. T (jω) = − (jω−P) / (jω + P) = (P−jω) · (P−jω) / (P + jω) · (P−jω) = (P ² −ω ² ) / (P ² + ω ^{2) + (- 2Pωj) /} (P 2 + ω 2) | T (jω) | 2 = [ReT (jω)] ² + [ImT (jω)] ² = ^{[(P 2 -ω 2) / (} P 2 + Ω ² )] ² + [(− 2Pωj) / (P ² + ω ² )] ² = (P ² + ω ² ) ² / (P ² −ω ² ) ² = 1 (5) On the other hand, (5) As is clear from the transfer function of the equation (1), the embodiment of FIG. 1 indicates that the filter is a first-order all-pass filter.

The all-pass filter shown in FIG.
By the output terminal of the supplies to the two non-inverting input terminal of the operational amplifier A _2, if is the same embodiment as the mutual conductance gm of Figure 1, it is half the capacitance of the capacitor C ₁ of the integrator 3 You can do it.

FIG. 4 shows the characteristics of the first-order all-pass filter shown in FIG. Variable conductance amplifier supplies an operating current to A _1, as the characteristic curve of the delay time at a frequency of 1MHz was varied in the range of 3b 4b of the characteristic curve of the amplitude characteristic is a change from 3a to 4a It is much more stable than the conventional example. It is possible to obtain a practically acceptable characteristic up to about 3 MHz.

[0012]

[Effect of the invention] The all-pass filter of the invention is shown in FIG.
Alternatively, even if the group delay characteristic is varied by adopting the configuration shown in FIG. 2, the amplitude characteristic can be made stable and extremely effective. or,
When an active filter is configured in combination with another filter, the filter characteristics can be adjusted, so that extremely stable characteristics can be obtained.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing an embodiment of an all-pass filter according to the present invention.

FIG. 2 is a circuit diagram showing another embodiment of the all-pass filter according to the present invention.

FIG. 3 is a block diagram of the all-pass filter of the present invention.

FIG. 4 is a diagram for explaining a group delay characteristic and an amplitude characteristic of the all-pass filter of the present invention.

FIG. 5 is a circuit diagram showing an example of a conventional all-pass filter.

[Explanation of symbols]

1 input terminal 2 output terminal 3 integrator 4 adder A ₁ variable conductance amplifier A ₂ operational amplifier C ₁ capacitor

Continuation of the front page (72) Inventor Isao Fukai 18th Gomigaya, Tsurugashima-cho, Iruma-gun, Saitama Prefecture Toko Co., Ltd. Saitama Plant (56) References JP-A-58-151110 (JP, A) JP-A-52 -142949 (JP, A) JP-A-61-220517 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) H03H 11/04-11/22

Claims (1)

(57) [Scope of request for utility model registration] 1. An integrator comprising a variable conductance amplifier and a capacitor, and a negative feedback type operational amplifier to which an output of the integrator is supplied, and an input terminal having a non-inverting input terminal of the variable conductance amplifier and the operational amplifier. And the output of the integrator is connected to the first inverting input terminal of the operational amplifier.
And a non-inverting input of at least one side of a second non-inverting input terminal
And the output terminal of the operational amplifier is connected to the inverting input terminal of the variable conductance amplifier and the negative feedback of the operational amplifier.
An all-pass filter connected to a second inverting input terminal for forming a circuit .