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BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a circuit diagram showing an output
impedance control circuit according to the prior art, and FIG. 2 is a circuit diagram showing an
embodiment of the output impedance control circuit according to the present invention.
′Zs1. Zs2: Impedance element, VRt: Variable resistor, R1, Load: R1-R3: Resistance, El:
Positive power supply, A1: Amplifier, R2: Negative power supply.
DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an output
impedance control circuit that can be made negative to the output impedance of an amplifier.
Conventionally, various output impedance control circuits capable of achieving zero output
impedance by canceling out the impedance component of the speaker cord for connecting the
speaker to the auio amplifier temple have been announced, as shown in FIG. 1 Also shown is a
representative example. This circuit detects the output signal current of the amplifier A1o with a
resistor Rs connected between the load R1, ··· and the ground 2 and the detection current is
inverted and amplified with the amplifier All to make a voltage negative return of the amplifier Al
·. In the configuration to be applied to the ring loop, the current return amount by the detection
current is continuously changed from negative to 0 to positive by adjustment of the variable
resistor VR,. The output impedance of the amplifier A16 may be changed continuously from
positive to zero. However, in this circuit, an inverting amplifier is required for current return, and
the circuit is also complicated, which is disadvantageous in terms of cost and production.
SUMMARY OF THE INVENTION The present invention overcomes the disadvantages of the prior
art, and its object is to provide an output kinobeadance control circuit purple of an amplifier
having a simple circuit configuration without requiring an active element for current return. An
embodiment of the present invention will be described below with reference to FIG. In the figure,
A1 is an amplifier and has a voltage negative feedback loop by resistors Rv and Rs, and a load Bt
is connected to the output of the amplifier AI via an impedance Zzk such as a speaker cord etc.
There is. A first impedance element zsl is connected between the load RL and the ground, rvoEl is
a positive power supply for the amplifier, E2 is a negative power supply for the amplifier, and the
positive poles of E 負 -N and B2 are mutually connected. It is connected, and this connection
point is grounded to a 1-piece,-ヱ 6 ground via a second impedance element. Furthermore, the
two fixed ends of the variable resistor VRI are connected n between the other ends of each of the
two I-1-impedance elements not on the common ground side of the two, while the slider end is
the reverse phase of the amplifier AI. The input 4jK is connected. The output impedance control
circuit of the present invention is constituted by the above Zst + Zsz + VR +. In the figure, rl + rfi
represents the resistance value divided by the slider of the variable resistor VR1 as Q,
respectively, and each reference symbol also represents the element power of each element.
Further, in the figure, Va represents an input terminal and an input voltage, and Vo represents an
output voltage.
In such a configuration, in the case of R1 >> r ++ rz >> Zst + z12, the following relationship is
established between the valley element width and the voltage of the valley. Zstv 8 VO + z 2 +
Fatty IV OV 8 ′ ′ ′ ′ K; = R 2 ·· − 2 Vo + on, □ ′ V. ZstR4r ++ ra2a + R / a ,,, 1) If I arrange
IC and obtain the transfer function of the circuit, RIRs + & Rs + & & (Zs + R4) 7-bile □ medical
cord-ml-11 (Z * + Rt1) "i, (rs + r *)- (2 + Therefore, the output impedance of the amplifier Zo is
expressed by equation (2) シ, zO: ((r ++ r * R R * + R 鵞) rt & Z ml-rs Ba Zm z & (rx + r *) = (r ++ rt)
(Rt " One stop force ... (8) R + (ri + r *). Here, the right side of this M (3) equation is rewritten to 1,
2, and n * J! Force-proof Zo-one "Force wood 124 is 1 □ Force for □-(3) -mm (R1 R2) ZB1 and,
regarding the second term of the right-hand side of this formula, & (Zs ++ Zs + 1) If K− (r1 + r2
is L & + &) Zst
′ ′, rt / (r ++ rx) in this formula is 1. IIJ Continuous change from 0 to 1Q
due to the adjustment of the slider of the removable resistance 潴 VR + f 7). Therefore, in the
equation (4), 1.0 and the value of K is 0 ≦? (5) Since the right side of the equation (5) is larger
than 1 ',:! , 5 ζ □ ツ シ ノ 値 4 例 え ば value, for example, 2 v If it is said that adjusting the
VR1 to change the value of K in the range of 0 ≦ 2 in the range of ≦ 2 Then, according to the
relationship between the equation (4) and the equation (3), the value of Zo in the case of O
changes continuously in the range of 1 匪 匪 2 2 ≦ J Jt 16) 1 It is better than V. In other words,
it is possible to adjust the value of Rt * fhlt appropriately by setting the value of Oυ 臥 1 and the
value of output in-vidance Zo to be continuous 0 to negative and negative vcf by port 11m device
VRIK. It will be. Slightly adjust the variable resistor so that the unnecessary impedance
component Zs of the speaker code etc. which enters the series vc output circuit with the load RLs
without fail when amplifying 6ArVC load R1, all connections become Zo = -Z * If it is possible to
offset isometrically in the above case G mentioned above, the output impedance control circuit
according to the present invention may set the output impedance of the amplifier using it
positive to 0 to negative. Since the variable control can be continuously performed, it is possible
to cancel out the unnecessary speaker cord etc., → 6 components, and therefore it is possible to
ideally apply the output signal of the amplifier to the load. It is said that the current positive
feedback (Q7t active element is unnecessary and the circuit configuration is extremely simple
and the VC configuration is extremely advantageous in cost and production) while having the
same function as the conventional similar circuit. Features Those having.