JPS6138278Y2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a signal characteristic adjustment circuit suitable for use in, for example, a circuit for cutting off a DC component contained in the output of an amplifier or a filter circuit.

For example, the circuit shown in FIG. 1 has been mainly used as a circuit for cutting off the DC component contained in an amplifier. In this circuit, the DC component included in the output of the amplifier 1 is cut off by the capacitor 2, and only the AC component of the output of the amplifier 1 is supplied to the load 4 via the output terminal 3. In this case, in order to improve the low frequency characteristics, especially when the impedance of the load 4 is low, the capacitance of the capacitor 2 must be increased, so the shape of the capacitor 2 becomes large, or the capacitor 2 has a large capacitance. When electrolytic capacitors were used, there were problems such as unstable characteristics.

In addition, there is a conventional filter circuit (high-pass filter) shown in Fig. 2, but in order to extend the frequency characteristics to the low range in this circuit, the capacitance of the capacitor 5 must be increased. Therefore, the same problem as in the case of the circuit shown in FIG. 1 has occurred.

In view of the above-mentioned circumstances, this invention provides a signal characteristic adjustment circuit that can configure a circuit or filter circuit for cutting off the DC component contained in the output of an amplifier without using a large-capacity capacitor.
an inverting amplifier, a first element with impedance Z ₁ inserted between the input terminal and the input terminal of the inverting amplifier, and a second element with impedance Z ₂ inserted between the input and output terminals of the inverting amplifier. a third element with impedance Z ₃ inserted between the output terminal and the output terminal of the inverting amplifier; and a fourth element with impedance Z ₄ inserted between the input terminal and the output terminal. and a relationship of [Z ₁ Z ₃ =Z ₂ Z ₄ ] between the impedances of the first to fourth elements with respect to a specific frequency component of the input signal applied to the input terminal. This is a characteristic feature.

In particular, the first, third, and fourth elements are resistors with low resistance values _R1 , _R3 , and _R4 , respectively, and the second
The element is equivalently a circuit in which a low resistor with a low resistive value R ₂ and a capacitor with a capacitance C are connected in parallel, and when the input signal is DC, the relationship is R ₁ R ₃ = R ₂ R ₄ . Features.

Next, embodiments of this invention will be described with reference to the drawings. FIG. 3 is a circuit diagram showing the configuration of a circuit for cutting off the DC output component of an amplifier which is an embodiment of this invention. In this figure, terminal 11 is connected to the input terminal of amplifier 12. The output terminal is connected to an input terminal 14 of a signal characteristic adjustment circuit 13. This input terminal 14
is connected to the output terminal 16 via the resistor 15 (value R ₄ ) (fourth element), and is connected to the output terminal 16 via the resistor 17 (value R 4 ).
R ₁ ) (first element) to the inverting input terminal of the operational amplifier 18, and a resistor 19 (value R ₂ ) and a capacitor 20 (capacitance C ) are inserted in parallel, the non-inverting input terminal of the operational amplifier 18 is grounded, and a resistor 21 (value R ₃ ) (third element) is interposed between the output terminal of the operational amplifier 18 and the output terminal 16. It is designed to be inserted. The resistor 19 and capacitor 20 constitute a third element, and between the values of the resistors 15, 17, 19, and 21, R ₁ R ₃ =R ₂ R ₄ (1) A relationship is established. Further, the amplifier 12 is an amplifier having a DC output or a DC potential at its output end, and the operational amplifier 18 is an amplifier with almost no output offset shift.

Therefore, in the above circuit, the voltage at the input terminal 14 is V ₁ , the output voltage of the operational amplifier 18 is V ₂ , the voltage at the output terminal 16 is V ₀ , and the voltage at the input terminal 14 is V 1 .
If the signal obtained in is DC, the impedance of the capacitor 20 is considered to be ∞, so V ₂ = -R ₂ /R ₁ V ₁ ...(2) V ₀ =V ₁ R ₃ +V ₂ R ₄ /R ₃ +R ₄ ...(3) The following formula holds true. Substituting the above equations (3) and (2), V ₀ =V ₁ (R ₁ R ₃ −R ₂ R ₄ )/R ₁ (R ₃ +R ₄
)…(4) is obtained. By substituting the above equation (1) into this equation (4), the following is obtained: V ₀ =0 (5). That is, the circuit shown in FIG. 3 can completely cut out the DC component contained in the output of the amplifier 12.

Next, when considering the function of the signal characteristic adjustment circuit 13 for the alternating current component of the output of the amplifier 12, first, a circuit (a type of integrating circuit) composed of an operational amplifier 18, a resistor 17, a resistor 19, and a capacitor 20 is considered. ) has a characteristic of amplifying only the low frequency components of the signal obtained at the input terminal 14 and cutting out the high frequency components (that is, setting V ₂ =0). Then, the high cutoff frequency Fc is determined by Pc=1/2πCR ₂ (6). Therefore, input terminal 14
Output terminal 1 for input signal voltage V ₁ obtained at
The response of the output signal voltage V ₀ obtained in 6 is:
As mentioned above, when the input signal frequency is in the DC region, V ₀ = 0, and even in the very low frequency region, V ₀ = 0, and the input signal frequency is equal to the cut-off frequency.
When Fc is exceeded, V ₂ =0, so V ₀ =R ₃ /R ₃ +R ₄ V ₁ (7). This situation is illustrated in FIG. 4.

Therefore, from equation (6) above, by increasing the value R ₂ of the resistor 19, the cutoff frequency Fe can be made sufficiently small even if the capacitance C of the capacitor 20 is relatively small, and the low frequency characteristics can be improved. A signal characteristic adjustment circuit 13 that can cut extended DC components,
This can be realized using a capacitor 20 of relatively small capacity. The value R ₂ of the resistance resistor 19 can be selected quite freely as long as it satisfies the relationship of equation (1).

In addition, if the frequency of the signal obtained at the input terminal 14 is high, as can be seen from equation (7) above, the resistors 15 and 21 should be set in advance so that [R ₄ ≪R ₃ ].
By selecting a value of , the signal obtained at the input terminal 14 can be efficiently transmitted to the output terminal 16.

On the other hand, in the circuit shown in FIG.
If an LCR resonant circuit or the like is inserted between the input and output terminals of the operational amplifier 18 instead of the capacitor 20, it is possible to form a filter circuit that transmits to the output terminal 16 only signals having a frequency equal to the resonant frequency of the LCR resonant circuit among the signals obtained at the input terminal 14, and attenuates signals having frequencies other than the resonant frequency.

As explained above, according to this invention, the first to fourth elements and the inverting amplifier are provided, and the first to fourth elements have [Z ₁ Z ₃ =
Z ₂ Z ₄ ] Since the structure is configured so that the equilibrium condition is satisfied, for example, a circuit that cuts the DC component of the input signal and whose frequency characteristics extend to extremely low frequencies for the AC component can be constructed using a large capacitor. It can be realized without using Therefore, for example, in a stereo amplifier or the like, by using a low capacitance capacitor with good sound quality, it is possible to obtain a high sound quality amplifier with frequency characteristics extended to the very low range. Furthermore, when this invention is used as a filter circuit, it has the advantage that the capacitor can be made smaller and the overall configuration can be made more compact.

[Brief explanation of drawings]

FIG. 1 is a diagram showing an example of a conventional DC component cutting circuit, FIG. 2 is a diagram showing an example of a conventional filter circuit, and FIG. 3 is a circuit diagram showing an embodiment of this invention. FIG. 4 is a diagram showing the response of the output voltage V ₀ to the input voltage V ₁ in the circuit shown in FIG. 3. 13... Signal characteristic adjustment circuit, 14... Input terminal, 15... Fourth element (resistance), 16... Output terminal, 17... First element (resistance), 18... Inverting amplifier, 19... ...Second element (resistance), 20...
...Second element (capacitor), 21...Third element (resistance).

Claims (1)

[Claims for Utility Model Registration] (1) An inverting amplifier and a first impedance Z ₁ inserted between the input terminal and the input terminal of the inverting amplifier.
a second element with impedance Z ₂ inserted between the input and output terminals of the inverting amplifier, and a third element with impedance Z ₃ inserted between the output terminal and the output terminal of the inverting amplifier. and a fourth element having an impedance of Z 4 inserted between the input terminal and the output terminal, and the fourth element has an impedance of Z ₄ which is inserted between the input terminal and the output terminal. A signal characteristic adjustment circuit characterized in that the impedances of the four elements have the following relationship: [Z ₁ Z ₃ =Z ₂ Z ₄ ]. (2) The first, third, and fourth elements are resistors with resistance values _R1 , _R3 , and _R4, respectively, and the second element is equivalently a resistor with a resistance value _R2 and a capacitance C. The signal characteristic adjustment according to claim 1 of the utility model registration claim, characterized in that the circuit is connected in parallel with a capacitor and the relationship is R ₁ R ₃ = R ₂ R ₄ when the input signal is DC. circuit.