JPH0140527B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an amplifier circuit, and particularly to a linear class B transconductance power amplifier circuit suitable for driving an inductive load.

It is often necessary to drive an inductive load linearly with an input signal voltage, for example convergence control of color television receivers or color graphics display devices is a typical example. The convergence control circuit applies a convergence control signal derived from a vertical or horizontal deflection signal, or both deflection signals, to a convergence coil. For example, if the deflection signal is X (-1≦X≦1), the convergence control signal is a composite signal of a parabolic waveform signal (KX ² , where K is a coefficient) and a static convergence signal.
Incidentally, in convergence control of an apparatus requiring high resolution, convergence control signals of a third order or higher order (X ³ , X ⁴ , . . . ) may be used.

To obtain the desired convergence control signal,
Typically, a function generator with multiple multipliers is used. The obtained convergence control voltage signal is amplified to an appropriate amplitude value and then converted into a current signal for driving the convergence coil.

FIG. 1 shows an example of a conventionally designed amplifier circuit used to drive an inductive load such as a convergence coil. In FIG. 1, an input signal e _io is applied to the input terminal INPUT from an input signal voltage source (not shown) whose power supply impedance is negligible, and is applied to the first differential operational amplifier A1 via resistors R11 and R21, respectively. and the non-inverting input terminal of the second differential operational amplifier A2. on the other hand,
The non-inverting input terminal of A1 and the inverting input terminal of A2 are connected to a reference voltage source such as ground (hereinafter referred to as ground) via resistors R12 and R22, respectively, and the non-inverting input terminal of A2 is connected via resistor R24. It is grounded. The output terminals of A1 and A2 are each transistor (hereinafter referred to as TR, but may be omitted) Q3.
and the bases of Q4, and the emitters of Q3 and Q4 are grounded through resistors R15 and R25. A feedback resistor R13 is connected between the inverting input terminal of A1 and the emitter of Q3, and the other feedback resistor R13 is connected between the inverting input terminal of A1 and the emitter of Q3.
23 is connected between the inverting input terminal of A2 and the emitter of Q4. Protection diodes D1 and D2 are provided between the bases and emitters of Q3 and Q4 to protect these TRs from reverse voltage. Inductive loads L1 and L2, which are, for example, convergence coils, are connected between Q3 and Q4 and the positive voltage source +Vcc, respectively.

Next, the operation of the circuit shown in FIG. 1 will be explained.
As is well known, due to the high internal gains of A1 and A2, a voltage of -e _io · R13 / R11 is generated at the emitter of Q3, and a voltage of e _io · R24 / R21 + R24 · R22 + R23 / R22 is generated at the emitter of Q4. occurs. In addition, R11, R13, R21, R22, R23, R24 are resistors R11, R13, R21, R22, R23,
The resistance of R24 is shown (hereinafter, the number with R in the formula shows the resistance of the corresponding resistor). During the positive period of the input signal e _io (e _io >0), Q4 and Q3 are in the on and off states, respectively, and the collector current of Q4 I _O2
is essentially expressed by the following equation (1).

I _O2 =R22+R23/R25・R22・R24/R21+R24e _io ...
…(1) If R23=R24 and R21=R22, I _O2 = R23/R25・R22e _io ………(1a) On the other hand, in the negative period of the input signal e _io (e _io <0),
Q3 and Q4 are turned on and off, respectively, and the collector current I _O1 of Q3 is substantially expressed by the following equation (2).

I _O1 = R13/R15・R11e _io ………(2) From the above explanation, in the circuit shown in Figure 1, the input signal
It turns out that in order to achieve linear operation over the positive and negative periods of e _io , ie over the entire operating range, it is necessary to select the parameters of the circuit elements very carefully.

Furthermore, in the circuit of FIG. 1, in order to equalize the operating states of differential amplifiers A1 and A2, it is necessary to equalize the impedances of the non-inverting and inverting input terminals. However, it has been difficult to satisfy this requirement.

SUMMARY OF THE INVENTION It is therefore an object of the present invention to overcome the drawbacks of the above-mentioned circuits and to provide an amplifier circuit, in particular a linear class B transconductance amplifier circuit, which is most suitable for driving a convergence coil.

Hereinafter, the amplifier circuit according to the present invention will be explained with reference to FIGS. 2 and 3. In the embodiment of the invention shown in FIG. 2, the input signal e _io is passed through the input terminal INPUT and the resistor R11 to the second TRQ2, which together with the second TRQ2 constitutes an emitter-coupled transistor pair, ie, a differential amplifier.
1Apply to the base of TRQ1. The emitters of Q1 and Q2 are directly connected and connected to a common current source I _K ,
The base of is connected to the positive voltage source V _CC through resistor R12. Similarly, the base of Q2 is resistor R2
It is connected to the positive voltage source V _CC through R21 and grounded through resistor R21. The collectors of Q1 and Q2 are connected to a diode D1 and a resistor R1, respectively.
4. Connected to the negative voltage source -V _EE through the diode D2 and resistor R24, and also connected to the bases of the third TRQ3 and the fourth TRQ4, respectively. The emitters of Q3 and Q4 are grounded through emitter resistors R15 and R25, respectively, and the collectors are connected to a positive voltage source V _S through inductive loads L1 and L2, respectively. A feedback resistor R13 is connected between the base of Q1 and the emitter of Q3, while another feedback resistor R23 is connected between the base of Q2 and the emitter of Q4. Note that OUT1 and OUT2 are output terminals that output voltages proportional to the load currents I ₀₁ and I ₀₂ as necessary to obtain, for example, a convergence control signal.

Next, the operation of the circuit shown in FIG. 2 will be explained.
The TR pair Q1, Q2 and the current source _IK constitute a differential amplifier. When the input signal e _io is negative, Q4 is off and Q1, Q2, Q3 and the resistors connected to these TRs form an inverter and the output terminal
Output voltage -e _io・R to OUT1, that is, the emitter of Q3
13/R11 appears. Therefore, the collector current (output current) I _O1 of Q3 is determined by the above equation (2). Of course, the collector current (output current) I _O2 of Q4 is zero when the input signal e _io is negative. On the other hand, when the input signal e _io is positive, Q3 is turned off, and Q1, Q2, and Q4 constitute a non-inverting amplifier. The resistances of the resistors R11, R12, and R13 are made substantially equal to the resistances of the resistors R21, R22, and R23, respectively, and resistors having the same characteristics are used for Q1 and Q2. As the voltage of the input signal e _io increases, the emitter current of Q1 decreases and the emitter current of Q2 increases. Therefore, the collector voltage of Q2 is amplified by Q4, and Q4
Output current I _O2 flows through the collector of. That is, Q2
The collector voltage of is converted to the collector current I _O2 of Q4.

If the base current of TRQ1 is i, (1+β)
i flows from that emitter to the emitter of TRQ2. The collector currents of TRQ1 and TRQ2 both have equal amplitude (but opposite polarity). This TRQ2
Substantially all of the collector current βi of the diode D
2 and collector resistor R24, producing a voltage drop or signal voltage. This signal voltage appears as an output voltage V ₀₂ at the emitter of TRQ4, but it also appears as an output voltage V 02 at the emitter of TRQ4.
The base-emitter junction voltages of TRQ4 are substantially canceled. Therefore, V ₀₂ βiR24.

Here, the base voltages of TRQ1 and Q2 are also substantially equal. Assuming R13≫R15, the base voltage of TRQ1 (and therefore the base voltage of Q2) e′ _{io is} equal to
It is a value obtained by dividing the voltage by three parallel combined resistors R12R13, and is given by the following formula.

e′ _io =R12R13/R11+R12R13e _io =R12
・R13/R11 (R12+R13)+R12・R13e _io On the other hand, the base signal current of TRQ2 is i,
This is the parallel combined resistance R2 of resistors R21 and R22.
This is the sum of the current e' _io /(R21R22) flowing through R22 and the current (e' _io -V ₀₂ )/R23 flowing through the feedback resistor R23. Therefore, by substituting this value for i in the formula for V ₀₂ above, V ₀₂ β(R21+R22/R21・R22e′ _io +e′ _io −V _O2 /R23
)R24 If the above equation is further rearranged using V _O2 , V _O2 β(R21+R22/R21・R22+1/R23)/1+βR2
4/R23R24e′ _io β≫1, then V ₀₂ (R21+R22/R21・R22R23+1)e′ _io By substituting the above value of e′ _io into this equation, the following equation (3) is obtained.

V _O2 = e _io R21・R22+R21・R23+R22・R23/R21・R22
・R12・R13/R11・R12+R11・R13+R12・R13……(3) Here, in the above formula (3), R21, R22 and R
By substituting R11, R12, and R13 into 23, equation (3) becomes as follows.

V _O2 = e _io R13/R11 ………(4) Diode D2 is the base of transistor Q4.
In addition to compensating the junction voltage between emitters, it also has a temperature compensation function. Note that the inductive loads L1 and L2 are connected in opposite directions to the positive voltage source V _S so that they operate in opposition.

FIG. 3 is a circuit diagram showing a specific example of an amplifier circuit according to the present invention. The circuit in Figure 3 consists of TRQ5 and Q
The circuit is essentially the same as that of FIG. 2, except for the addition of a middle current amplification or emitter-follower stage with diodes D3-D6, a saturation prevention circuit P with diodes D3-D6, and a current limiting circuit with TRQ7 and Q8. are the same.

The emituta-holoa stage consisting of Q5 and Q6 is
Since the signal source impedance of the drive circuit of the output stages TRQ3 and Q4 is reduced, the responsiveness of the circuit can be improved. Saturation prevention circuit P outputs
It is used to clamp the collector voltages of TRQ3 and Q4 to a predetermined voltage V _L determined by the reference voltage V _L. Current limiting circuitry Q7 and Q8 effectively protect the circuit elements by determining the maximum current in Q3 and Q4 during the application of excessive or transient input signals. For example, when the collector output current of Q3 approaches a limit value, the voltage across R15 applied to the base of Q7 via R19 turns on Q7 and reduces the base drive current of Q3. This limiting current I _LIM is given by the following equation.

I _LIM =V _D7 +V _BE7 /R15 (5) Here, V _D7 and V _BE7 are the voltage drop of diode D7 and the base-emitter voltage of TRQ7, respectively.

Incidentally, the current limit of Q4 is similarly caused by R29, Q8 and D8. Since the other circuits are substantially the same as those in FIG. 2, detailed explanation will be omitted here.

As is clear from the above explanation, the amplifier circuit of the present invention responds to TRQ1 and Q3 for negative polarity input signals.
and the attached circuit elements constitute an inverting amplifier, and OUT1
It outputs a signal voltage determined by −e _io ·R13/R11 and flows a load current corresponding to the load L1. Also, for positive input signals, TRQ1,
A non-inverting amplifier is configured by Q2 and Q4 and the attached circuit elements, and a signal voltage equal to e _io ·R13/R11 is output to OUT2, and a load current corresponding to load L2 is caused to flow. Therefore, this amplifier circuit is completely B
Since the gain (or amplification characteristic) for positive and negative signals can be made the same, high efficiency and a wide operating range (dynamic range) can be obtained. Furthermore, the circuit configuration is relatively simple as it consists of four TRs and attached elements.

Although the preferred embodiment of the present invention has been described above, those skilled in the art can easily modify the present embodiment according to the intended use. The present invention can be applied to any amplifier that converts an input signal voltage into an output current. Incidentally, in the above-mentioned embodiment, an inductive load was explained, but it is natural that the present invention is not limited to an inductive load. Furthermore, it should be noted that by using a common load for both TRQ3 and Q4, the circuit according to the invention can be used as an amplifier that outputs the absolute value of the signal. In this case, the output current flowing to the common load is proportional to the absolute value of the input signal. Incidentally, an amplifier that outputs the absolute value of a signal is suitable for application in various fields, particularly in waveform conversion circuits.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram of a conventional amplifier circuit, and FIGS. 2 and 3 are circuit diagrams of an amplifier circuit according to the present invention. Q1 to Q9...transistor, R15, R25
...Emitter resistor, R13, R23...Feedback resistor, L1, L2...Load.

Claims (1)

[Claims] 1. The first and second terminals have their emitters commonly connected to a constant current source and their collectors connected to the power supply through respective resistors.
a transistor, and third and fourth transistors each having a base connected to the collector of the first and second transistors, an emitter connected to a reference voltage source via an emitter resistor, and a collector connected to a load, respectively. a feedback resistor having equal resistance connected between the bases and emitters of the first and third transistors and the second and fourth transistors; an amplifier circuit for applying a signal and having the base of said second transistor connected to a reference voltage source through a resistor substantially equal to said input resistor.