JPH05304427A - Current output amplifier circuit - Google Patents

Abstract

PURPOSE:To make frequency characteristic constant regardless of ambient temperature. CONSTITUTION:Power supply voltage is divided by resistances R1, R2, the split voltage is made the input bias voltage of a differential amplifier CA1 and an input signal is supplied to the noninverted input terminal from an input terminal T1. The output signal of a differential amplifier VA1 is amplified in a current output amplifier CA1 provided with a feedback resistance R5 to an inverted input terminal and is outputted to an output terminal T3. A common capacitor C1 is connected between the connection point of the resistances R1, R2, the inverted input terminal of the current output amplifier CA1 and a ground terminal T4. As a result, standard voltage source is possible to be made into low impedance and the leakage to the standard voltage source is possible to be reduced by the signal voltage adding a power supply voltage line.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention mainly relates to a current output amplifier circuit used in an electromagnetic conversion system such as a video tape recorder.

[0002]

2. Description of the Related Art An example of a conventional current output amplifier circuit is shown in FIG.

In FIG. 2, T ₁ is an input terminal, T ₂ is a power supply voltage terminal, T ₃ is a current output terminal, T ₄ is a ground terminal, and T ₅ is a DC feedback terminal. The voltage signal input from T ₁ is amplified by the differential amplifier of the first stage, converted into a current signal by the resistor R ₇ of the current output amplification circuit of the next stage, and passed through the current mirror circuit and the capacitance C ₂ to load the load. It is output to R ₉ . The input voltage signal is v _i and the output of the first stage differential amplifier is v _o .
The voltage amplification degree G _V of the first stage differential amplifier is expressed by the following equation.

[0004]

[Equation 1]

However, k is the Boltzmann constant, T is the absolute temperature, and q is the charge amount of electrons. The output current of the current output amplifier circuit of the next stage is given by the following equation.

[0006]

[Equation 2]

However, M is the mirror ratio of Q ₆ and Q ₉ , and the mirror ratio of Q ₁₀ and Q ₁₁ , which are set by changing the emitter size of T _r .

Therefore, the voltage-current conversion ratio G _{i of} this circuit is
Is

[0009]

[Equation 3]

[0010] An output current signal is output with respect to the input voltage signal based on the conversion ratio.

[0011]

In the circuit configuration shown in FIG. 2, in order to obtain a large current output and to reduce the circuit current, a mirror ratio of about 10 times is generally taken and voltage-current conversion is performed. The ratio G _i is increased and used. for that reason,
The current signal shown below flows through the power supply voltage line.

[0012]

[Equation 4]

The power supply voltage line is separated by an LC filter so as not to interfere with another circuit using the same line, but the resistance component equivalent to the capacitance or the resistance component of the inductance and the pattern. Resistance component,
Since a voltage amplitude is generated in the power supply voltage line of the circuit, resonance occurs in this filter, and an abnormal peak or a dent is generated in the low frequency band of the amplitude frequency characteristic of the power supply voltage line. This phenomenon becomes more remarkable as the ambient temperature decreases and the loss resistance component of the capacitance of the power supply filter increases. With respect to the amplitude of the power supply voltage line, the reference voltage, which is configured by dividing the power supply voltage and ground by resistance division with R ₁ and R ₂ , is oscillated, and is amplified by the first stage differential amplifier to reduce the output current frequency characteristic. Abnormal peaks or dents occur in the frequency band.

The present invention solves the above-mentioned conventional problems. It is possible to prevent the influence on the frequency characteristic by making the reference voltage low impedance without increasing the elements by using the existing capacitance. To aim.

[0015]

SUMMARY OF THE INVENTION The present invention is summarized as follows.
The non-inverting input terminal of the first differential amplifier is connected to the input terminal and the first resistor, the inverting input terminal of the first differential amplifier is connected to the second resistor, and the first resistor and the second resistor are connected. The other end of the resistor is commonly connected to the midpoint of the third and fourth resistors connected in series between the power supply voltage terminal and the ground terminal, and the output of the first differential amplifier is connected to the first differential amplifier. Connected to the non-inverting input terminal of the current output amplifier, connecting the output terminal of the first current output amplifier and the inverting input terminal through a fifth resistor, and connecting the inverting input terminal of the first current output amplifier to the The circuit configuration is such that it is connected to the ground terminal through one capacitance and is connected to the midpoint of the third and fourth resistors.

[0016]

According to the present invention, with the above-described structure, the reference voltage can be created with a low impedance, and the influence of the amplitude of the power supply voltage line is separated from the internal circuit, whereby the specified characteristics can be obtained.

[0017]

1 is a functional diagram of a current output amplifier circuit according to the present invention, and FIG. 3 shows an embodiment. 1 and 3, T ₁ is an input terminal, T ₂ is a power supply voltage terminal, T ₃ is a current output terminal, T ₄ is a ground terminal, and T ₅ is a DC feedback terminal.

The current of the present embodiment configured as described above
The operation of the output amplifier circuit is the same as the above-mentioned conventional example.
Issue V_i, Output current i_oAs input voltage-output current conversion
Ratio G _iIs shown as follows.

[0019]

[Equation 5]

Similarly, the signal current flowing through the power supply voltage line is

[0021]

[Equation 6]

It is indicated by. If the equivalent impedance of the power supply voltage line is Z, the voltage amplitude v of the power supply voltage line
_VCC is

[0023]

[Equation 7]

It becomes In the conventional example of FIG. 2, the output current with respect to the voltage amplitude is

[0025]

[Equation 8]

On the other hand, in the embodiment shown in FIG.

[0027]

[Equation 9]

[0028] Generally, in consideration of efficiency, the potential of the DC feedback terminal is set to ½ of the power supply voltage. Therefore, R ₁ = R ₂ = R, and at this time, the improvement ratio between the conventional example and the example is expressed by the following formula.

[0029]

[Equation 10]

Therefore, the influence of the fluctuation of the power supply voltage on the output current is greatly reduced.

[0031]

According to the present invention, the existing capacitance is used to lower the impedance of the reference voltage, and in particular, the influence on the frequency characteristic through the current-voltage line of the current output amplifier circuit which becomes a problem when the ambient temperature is lowered. Can be significantly reduced without increasing the number of elements.

[Brief description of drawings]

FIG. 1 is a block diagram of a current output amplifier circuit of the present invention.

FIG. 2 is a circuit diagram of a conventional example.

FIG. 3 is a circuit diagram of an embodiment of the present invention.

[Explanation of symbols]

 T₁ Input terminal T₂ Power supply voltage terminal T₃ Current output terminal T_Four Ground terminal T_Five DC feedback terminal R₁~ R₈ Resistance I₁~ I_Five Current source Q₁~ Q_Five, Q_Ten,Q₁₁ NPN transistor Q₆~ Q₉ PNP transistor C₁~ C_Four Capacity R₉ Load resistance L₁ Inductance V_A1Differential amplifier  C_A1 Current output amplifier

Claims (1)

[Claims] 1. A non-inverting input terminal of a first differential amplifier is connected to an input terminal and a first resistor, and an inverting input terminal of the first differential amplifier is connected to a second resistor, The other ends of the first resistor and the second resistor are commonly used, and the first resistor and the second resistor are connected to the middle point of the third and fourth resistors connected in series between the power supply voltage terminal and the ground terminal. The output of the dynamic amplifier is connected to the non-inverting input terminal of the first current output amplifier, the output terminal of the first current output amplifier and the inverting input terminal are connected through a fifth resistor, and the first A current output amplifier circuit in which an inverting input terminal of the current output amplifier is connected to a ground terminal through a first capacitor and is connected to a middle point of the third and fourth resistors.