JPH09148850A - Composite wide band amplifier - Google Patents

Abstract

(57) An upper limit frequency of operation of a composite wide-band amplifier including a DC high-precision amplifier, a differential amplifier, a voltage amplifier, and a current amplifier is conventionally limited by the bandwidth of the differential amplifier. An object of the present invention is to provide a wide band amplifier which is not restricted by the bandwidth of the differential amplifier. SOLUTION: A differential amplifier, a voltage amplifier, and a current amplifier are each constituted by individual parts, and two systems are symmetrically paired with respect to a zero potential when there is no signal, and are arranged in two systems. A high-pass filter is provided so that an input signal having a frequency higher than the frequency at which the voltage gain of the differential amplifier becomes 1 is bypassed to the differential amplifier and added to the voltage amplifier.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a composite wide band amplifier capable of handling DC signals as well as AC signals having a relatively high frequency.

[0002]

2. Description of the Related Art For an amplifier that receives a DC signal or an AC signal of a relatively low frequency, generally, the noise voltage of the device itself is low, the offset voltage and its temperature drift are small, and a large common mode rejection ratio (CMRR). Are needed. Further, for a device that inputs a relatively high frequency signal, a fast slew rate and a large G
It is desired to have a B product (gain x bandwidth).

In this case, since it is difficult to satisfy the above-mentioned desired characteristics with one amplifier, generally, an amplifier that operates with high precision in an AC signal region of DC and relatively low frequency, The device is configured by combining with an amplifier capable of high-speed operation in a high frequency region.

An example of this is shown in FIG.
For example, a DC high-precision amplifier (hereinafter, referred to as “high-precision amplifier”) A1 using an IC element, a high-speed differential amplifier A2, a voltage amplifier A3, and a current amplifier A4, which similarly each use an IC element, are provided. Therefore, the current amplifier A4 drives a unit in the subsequent stage (not shown). Here, R1 and R2 are input resistances, R3 is a feedback resistance, and C
1 is a coupling capacitor, Vi is an input signal, and Vo is an output signal.

In the above apparatus, when the input signal voltage (hereinafter referred to as "input voltage") Vi is a direct current and a relatively low frequency alternating current signal, each of the amplifiers A2 to A4 outputs the output from the pre-stage amplifier. It receives signals and operates in cascade. That is, when the input voltage Vi is applied to the high precision amplifier A1 via the resistors R1 and R2, the inverted output thereof is applied to, for example, the + input terminal of the differential amplifier A2. Further, the input voltage Vi is applied to the-input terminal of the differential amplifier A2 via the resistor R1. The differential amplifier A2 receives these signals and outputs the voltage signal of the difference to the voltage amplifier A3. The voltage amplifier A3 amplifies this signal voltage and current amplifier A4.
In addition, the current amplifier A4 is adapted to convert an input voltage signal into a current signal, amplify it, and output it.

When the frequency of the input voltage Vi increases, the gain of the high precision amplifier A1 decreases in inverse proportion to the frequency, and the output voltage decreases accordingly. Further, the reactance of the capacitor C1 also decreases in inverse proportion to it as the frequency increases, so that if the frequency exceeds a certain frequency, the − input terminal of the high precision amplifier A1 and the + input terminal of the differential amplifier A2 are in a direct communication state. Therefore, the input voltage Vi to the device is, on the one hand, applied through the resistor R1 to the negative input terminal of the differential amplifier A2,
On the other hand, the input voltage Vi passing through the resistors R1 and R2 bypasses the high-precision amplifier A1 whose gain has been lowered by the capacitor C1 and is applied to the + input terminal of the differential amplifier A2.

That is, in the band higher than a certain frequency, the high precision amplifier A1 does not contribute to the operation of the device, and the differential amplifier A2, the voltage amplifier A3 and the current amplifier A4 continue to operate. In order to clarify the problem to be solved, the frequency of the input voltage and the operations of the precision amplifier A1 and the differential amplifier A2 will be further described.

[0008] b. When the input signal is direct current From FIG. 5A, the high precision amplifier A1 and the differential amplifier A2
It is assumed that, in FIG. 2B, which is a transcription of the above portion, for example, a positive voltage + Vi of a certain level is applied from the signal source to the device. Here, assuming that the high-precision amplifier A1 is operating normally and its − input terminal is grounded to the + input terminal by an imaginary short circuit, the resistance R from the signal source is
A constant direct current I of I = Vi / (R1 + R2) flows through 1 and R2 toward the −input terminal of the high precision amplifier A1.

However, in the high-precision amplifier A1, the − input terminal is not directly connected to the + input terminal, so that the current I flows into the capacitor C1 and charges the same. This charging voltage is + Vc. Assuming that the capacitance of the capacitor C1 is C1 and the charge flowing into the capacitor by the current I is Q, the voltage Vc charged in the capacitor by this charge is Vc = Q / C1. The high-precision amplifier A1 emits a DC voltage −Vc from the output terminal of which the polarity of the charging voltage is inverted, and absorbs the same amount of charge as that flowing into the capacitor C1 from the same capacitor to increase the voltage on the −input terminal side. Hold down to ground potential.

Therefore, from the signal source Vi to the resistors R1 and R
The current I flowing through the capacitor C1 through 2 apparently flows into the inside from the output terminal of the high precision amplifier A1 through the same capacitor. In this case, the high-precision amplifier A1 operates as a normal inverting amplifier as described above, and when its gain is G1, G1 = Vc / Vi. The polarity reversal voltage −Vc is + of the differential amplifier A1.
Added to the input terminal. In addition, the input voltage Vi is applied to the resistor R1.
And the voltage across R2 when divided by _R2
Then, this divided voltage is applied to the-input terminal of the differential amplifier A2. Here, assuming that the gain of the differential amplifier A1 is G2, the differential amplifier multiplies the voltage of the difference between the signal voltages input to these two terminals by G2 and sends it as the output voltage V2 to the voltage amplifier A3. That is, V2 = {-Vc-(+ _VR2 )} G2. Thus, when the input signal is DC, the differential amplifier A2 operates in cascade with respect to the high precision amplifier A1.

If the voltage of the signal source is -Vi, which has the opposite polarity to that of the example shown in the figure, the high-precision amplifier A1 outputs its inverted DC voltage + Vc, discharges a current in the direction opposite to the above, and charges the capacitor. Inflow. As a result, the voltage drop on the negative input terminal side is suppressed and the ground potential is maintained.
In this case, the output V2 of the differential amplifier A2 is V2 = {Vc-(- _VR2 )} G2.

B. When the input signal is an alternating current From FIG. 5A, the high-precision amplifier A1 and the differential amplifier A2
In FIG. 6 (A) in which the part of FIG.
1 is operating normally, and its-input terminal is assumed to be at ground potential due to an imaginary short circuit with the + input terminal. Now, the AC input voltage ± Vi of frequency f from the signal source
Is added to the device and a current I flows as shown by the dotted line in the figure, ± I = ± Vi / (R1 + R2) = ± Vi / R. However, R = R1 + R2.

Assuming that the reactance of the capacitor C1 is Xc, the voltage Vc generated in the capacitor due to the flow of the above current is ± Vc = ± I · Xc. The high-precision amplifier A1 outputs a voltage (-, +) Vc having a polarity opposite to the voltage ± Vc generated in this capacitor and feeds it back to the input side, and holds its-input terminal at the ground potential. Here, when the angular frequency of the input voltage Vi is ω, the reactance Xc of the capacitor is Xc = 1 / ωC1 = 1 / 2πfC1 However, since ω = 2πf, the magnitude of the reactance is inversely proportional to the height of the frequency f. Change. Now, if the frequency at which the reactance Xc of the capacitor is equal to the value of the input resistance R is fc, then R = Xc = 1 / 2πfcC1 and fc = 1 / 2πC1R. The change in the value of the reactance Xc with respect to the frequency f is shown in FIG. Here, assuming that the gain of the high-precision amplifier A1 when the input voltage Vi is an alternating current is G1, G1 = Xc / R. Therefore, when the signal frequency is fc, Xc = R, and the gain G1 is shown in FIG. As shown in (C), it is 1 or 0 dB. When the frequency is 1/10 of fc, the gain G1 is 10 times (20 dB), and the frequency is fc.
10 times, G1 becomes 1/10 (−20 dB).

By the way, the gain of the element itself of the high precision amplifier A1, that is, the open loop gain G1 has a large value of 100 dB in the direct current region as shown in FIG. It has a characteristic of decreasing in inverse proportion to. Assuming that the frequency at which this gain reduction starts is f1, the value of f1 varies depending on the type of element, but is generally in the order of one or two digits.

When a signal having a frequency 10 times higher than the frequency f1 enters, the gain G1 is 1/10 of that when the frequency is f1.
The gain G1 drops to 1/100 (-40 dB) when a signal whose frequency is 100 times higher is input. That is, the rate of gain decrease with respect to frequency is -20d.
It is B / dec.

The relationship between the open loop gain of the differential amplifier A2 and the frequency also differs depending on the type of element, but an example thereof is shown in FIG. In the illustrated example, the open loop gain G2 in the DC region is 80 dB, and the frequency at which the gain G2 starts to decrease in the AC region is f2. Comparing this with the characteristic of the high-precision amplifier A1, generally, the open loop gain in the DC region is G1> G2, and the frequency at which the open loop gain starts to decrease in the AC region is f1 <f2.

Now, the − input terminal of the high precision amplifier A1 and +
If an imaginary short circuit is established between the input terminals and the differential amplifier A2 is in cascade with respect to the high-precision amplifier A1, the open loop total gain G1 + G2 of both amplifiers from DC to AC frequency f1 is , 180 dB as shown by the alternate long and short dash line in FIG.

Here, R is set so that the frequency fc at which the gain G1 of the high precision amplifier A1 in FIG. 6 (C) is 1 or 0 dB is substantially equal to the frequency f1 in FIG. 7, for example.
When the values of C1 and C1 are set, the + gain in the frequency band lower than fc of FIG. 6C is suppressed to a constant value of 100 dB of the open loop gain G1 extending from the DC region in FIG.

Further, the gain reduction characteristic of −20 dB / dec in the frequency band higher than fc of FIG. 6C is shown in FIG.
, The open loop gain G1 is -20 dB / de
c is added. Therefore, the open loop gain G1 of the high precision amplifier A1 in the frequency band higher than f1 decreases at a rate of −40 dB / dec as shown by the broken line. Therefore, the open-loop total gain G1 + G2 in the frequency band from f1 to f2 also has the characteristic of decreasing -40 dB / dec.

Here, the gain G1 of the high precision amplifier A1.
Is reduced at a rate of −40 dB / dec and the frequency when the gain reaches 1, that is, 0 dB line is set to, for example, f3, the high-precision amplifier A1 and the differential amplifier A2 are opened in a band exceeding the frequency f2 to the frequency f3. The total loop gain has a characteristic of -60 dB / dec because -20 dB / dec of the differential amplifier A2 is added.

High-precision amplifier A1 at this frequency f3
The relationship between the input voltage Vi and the magnitude (absolute value) of the polarity inversion output voltage −Vc is Vc = Vi, and G1> 1 in the frequency band lower than f3, and thus Vc> Vi.

Therefore, the frequency of the input voltage Vi is f3.
In the following low band, by negatively feeding back the inverted output voltage −Vc to the input side via the capacitor C1, the − input terminal can be imaginarily shorted (grounded) to the + input terminal. This inverted output voltage -Vc is applied to the + input terminal of the differential amplifier A2 at the next stage.

However, the frequency of the input voltage Vi is f
In the band higher than 3, the gain G1 of the high precision amplifier A1 becomes smaller than 1, so that Vc <Vi. Incidentally, when the level of the input voltage Vi is standardized to a constant value of 1 as shown in FIG. 8, the magnitude (absolute value) of the inverted output voltage Vc in the band where the frequency of Vi is higher than f3 becomes as shown by the broken line. .

In FIG. 8, for example, when the frequency of the input voltage Vi is 1.4 times f3, the magnitude of the output voltage Vc becomes 0.5, and when the frequency of Vi becomes twice the f3, Vc.
Is about 0.25. Also, the frequency of Vi is f
When it is three times as large as 3, the magnitude of Vc becomes about 0.1, and when the frequency of Vi further increases, the magnitude of Vc approaches zero without limit.

Therefore, the frequency of the input voltage Vi is f3.
In the higher band, even if the high-precision amplifier A1 negatively feeds back its inverted output −Vc via the capacitor C1 to the input side, the feedback voltage is small, and the −input terminal cannot be made imaginary ground. Therefore, a voltage Vi-Vc, which is the difference between the input voltage and the feedback voltage, is generated at the-input terminal, passes through the low impedance capacitor C1, and is applied to the + input terminal of the differential amplifier A2.

That is, in the band where the frequency is higher than f3, the high-precision amplifier A1 does not contribute to the amplifying operation of the device, and the cascade operation of the high-precision amplifier and the differential amplifier disappears, and the differential amplifier A2 with respect to the input voltage Vi. It is the first operation unit. Here, when the frequency of the input voltage Vi is several times higher than f3, the feedback voltage -Vc of the high precision amplifier A1.
Is much smaller than the input voltage Vi, the difference voltage Vi-Vc applied to the + input terminal of the differential amplifier A2 can be regarded as substantially Vi from FIG.

Therefore, the open loop total gain G1 + G2 of the high precision amplifier A1 and the differential amplifier A2 in FIG. 7 deviates from the lowering characteristic of −60 dB / dec when the frequency becomes higher than f3, and the open loop characteristic of the differential amplifier A2. Asymptotic to G2. Now, assuming that a frequency several times higher than f3 is f4, the open-loop total gain G1 + G2 that deviates from the above-mentioned -60 dB / dec lowering characteristic coincides with the open-loop gain G2 of the differential amplifier A2 at the frequency f4, and is higher than f4. The open loop total gain in the high frequency band is G2 itself.

In the subsequent stage of the differential amplifier A2, as shown in FIG.
As shown in FIG. 3, a voltage amplifier A3 and a current amplifier A4 are provided, and these three amplifiers operate in cascade in a band where the frequency of the input voltage is f3 or higher.
In this case, for example, the feedback resistor R3 is connected from the output side of the current amplifier A4 to the input side of the device, so that G = R3 / R1 when the closed loop gain of the entire device is G.

Now, this closed loop gain G is set to, for example, 10d.
If it is set to B and is shown by a broken line in FIG. 7, the open loop gain G2 of the differential amplifier A2, which is the head unit, is -20 dB.
The frequency f5 at the intersection of the straight line that decreases at the rate of / dec and the 10 dB line is the bandwidth of this device.

[0030]

According to this conventional device, a highly accurate response to a DC signal and a high speed response to a high frequency signal are possible. However, the upper limit frequency is limited by the bandwidth of the differential amplifier A2, and it is difficult to extend the bandwidth beyond that. Therefore, there is a problem that even if there is a margin in speed and bandwidth of the voltage amplifier and the current amplifier in the subsequent stage, they cannot be fully utilized.

The present invention has been made in consideration of the above circumstances, and its object is to bypass the differential amplifier when the frequency of the input signal is higher than the upper limit frequency of the bandwidth of the differential amplifier. Another object of the present invention is to provide a composite wide band amplifier adapted to be added to a voltage amplifier.

[0032]

Therefore, in the present invention, as a means for solving the problem, for example, a high-pass filter is provided between the input side of the differential amplifier and the input side of the voltage amplifier, and the high-pass filter in the high frequency band of the differential amplifier is provided. The cutoff frequency of the high-pass filter is determined in consideration of the gain reduction characteristic.

[0033]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows the basic configuration of the present invention. In the figure, the high precision amplifier A1 is an IC similar to the conventional device.
An element is used, and the signal input unit including the high precision amplifier A1 has the same configuration as that of the conventional device. High precision amplifier A1
For example, two differential amplifiers A2a and A2b composed of individual parts are provided in the subsequent stage, and the input terminal of this device corresponding to the + input terminal of the IC differential amplifier in the conventional device is connected to the common wiring. A (+) mark is added to the
For the input terminals of this device corresponding to the input terminals, the common wiring is marked with (-).

[0034] The (-) to the input terminal of the common wiring side marked with indicia, for example, the input voltage divided voltage V _R2 of Vi applied, (+) high to the input terminals of the common wiring side with marked Feedback voltage -Vc from the precision amplifier A1 having the opposite polarity to Vi described above.
Is added. As a result, the differential amplifiers A2a and A2b operate in parallel with the input voltage, and their outputs are applied to the terminals of the voltage amplifiers A3a and A3b, respectively.

The voltage amplifiers A3a and A3b are both composed of individual components, and for example, a capacitor C2 and a resistor are provided between the other input terminal and the common wiring marked with (-) on the input side of the differential amplifier. Two high-pass filters FLa and FL composed of R8, capacitor C3, and resistor R10
b are provided respectively, and the cutoff frequencies of both filters are set to the same value.

The voltage amplifiers A3a and A3b receive outputs from the differential amplifiers A2a and A2b and operate in parallel, and the outputs thereof are current amplifiers A4a composed of individual parts.
And A4b, respectively. Current amplifier A4a, A
4b also operates in parallel and converts the voltage applied from the voltage amplifier into a current and outputs it.

An example of the block diagram of FIG. 1 represented by an equivalent circuit is shown in FIG. In FIG. 2, the differential amplifier A
2a is, for example, an NPN transistor Q1 with uniform characteristics
When there is no signal, that is, when the bases of both transistors are at zero potential, a constant idling current flows through the common resistor R4 on the emitter side. Therefore, its emitter voltage is constant.

Here, since the base currents of both transistors are extremely small compared to the collector currents, ignoring them,
When there is no signal, the collector current and the emitter current of the transistor Q1 are equal to each other, and similarly, the collector current and the emitter current of the transistor Q2 are also equal to each other, which is half the constant current flowing through the common resistor R4. In this case, a positive constant voltage drop occurs in the load resistor R5 of the transistor Q2.

Similarly to the above, the differential amplifier A2b is also composed of a differential pair of PNP transistors Q3 and Q4 having uniform characteristics, for example, and the common resistance R6 on the emitter side has the same resistance value as R4. When there is no signal, a constant idling current having the same magnitude as the current flowing in R4 flows in R6, and the emitter voltages of both transistors are constant.

When the base currents of the transistors Q3 and Q4 are ignored, the emitter current and the collector current of the transistor Q3 are equal to each other when there is no signal, and the emitter current and the collector current of the transistor Q4 are also equal to each other. It is half the magnitude of the constant current flowing in the. The load resistance R7 of the transistor Q4
Has a resistance value equal to that of the load resistance R5 of the transistor Q2, a negative constant voltage drop is generated in the resistance R7 whose absolute value is equal to the voltage drop of the resistance R5.

The two differential amplifiers A2a and A2b are both composed of a small number of individual components, and are symmetrically arranged with respect to the zero potential between the positive power source + Vcc and the negative power source -Vcc. . Therefore, compared with the conventional IC differential amplifier composed of integrated circuits such as a large number of transistors, the gain is low, but the distortion is small, the speed is high and the band is wide. Here, for example, when a positive input voltage Vi is applied to the device, a negative inverting output −Vc is sent from the high precision amplifier A1.
It is added to the bases of the transistors Q1 and Q3 via the common wiring marked with (+).

As a result, the base voltage of the transistor Q1 is lowered, the voltage between the base and the emitter is reduced, the base current is reduced, and the collector current is reduced. Further, in the transistor Q 3, when the base voltage decreases, the voltage between the base and the emitter increases, the base current increases, and the collector current increases.

In this case, since constant currents of equal magnitude flow in the common resistors R4 and R6, when the collector current of the transistor Q1 decreases, the collector current of the paired transistor Q2 increases accordingly. . This is equivalent to the fact that the positive voltage Vc, which is the reverse of the polarity of the voltage -Vc, is applied to the base of the transistor Q2, and the base-emitter voltage thereof increases.

When the collector current of the transistor Q3 increases, the collector current of the paired transistor Q4 decreases accordingly. This means that the base of the transistor Q4 has a positive voltage Vc obtained by inverting the polarity of the voltage -Vc.
Is added, and the voltage between the base and the emitter is reduced.

That is, the decrease of the collector current of the transistor Q1 and the increase of the collector current of the transistor Q3 correspond to the increase of the collector current of the transistor Q2 and the decrease of the collector current of the transistor Q4, so that the transistor Q1 is connected via the common wiring (+). The negative voltage −Vc applied to the base side of Q3 and Q3 can be replaced with the positive voltage Vc applied to the base side of the transistors Q2 and Q4 via the common wiring marked with (−).

In this case, the divided voltage VR2 of the input voltage Vi is applied to the base side of the transistors Q2 and Q4 via the common wiring (-), but is smaller than the positive voltage Vc applied to the bases, so The collector current flowing through Q2 and Q4 is dominated by the voltage Vc. Note that the in-phase disturbance noise + Vn due to induction or the like is transmitted from the common wiring marked with (+) and the common wiring marked with (−) respectively to the transistor Q.
When added to the base of 1, Q3 and the base of Q2, Q4, Q
The disturbance noise + Vn added to the base of 1 and Q3 is Q2 and Q
It is functionally equivalent to the addition of -Vn whose polarity is inverted to the base of No. 4. However, the base of Q2 and Q4 is +
The disturbance noise of Vn is added and cancels each other, so that the influence is extremely small.

The voltage amplifiers A3a and A3b are, for example, PNPs.
-Type transistor Q5 and NPN-type transistor Q6 are connected complementarily via diodes D1 to D4, and the emitter of transistor Q5 is connected to the collector side of transistor Q2 of the first differential amplifier A2a. The emitter of the transistor Q6 is the second
Is connected to the collector side of the transistor Q4 of the differential amplifier A2b. In order to supply the base voltage to the transistors Q5 and Q6, for example, three resistors R8, R9 and R10 for dividing the voltage between the + Vcc power source and the −Vcc power source are provided, and the resistors R8 and R10 have the same resistance value. ing.

When there is no signal, transistors Q5 and Q
When the base voltage is supplied to 6, the + Vcc power source supplies the resistor R5, the transistor Q5, the diodes D1 to D4,
A constant idling current flows to the -Vcc power supply through the transistor Q6 and the resistor R7, and a voltage drop occurs in each of the resistors and the diode.

In this case, the emitter voltage and the collector voltage of the transistor Q5 have positive values, and the emitter voltage and the collector voltage of the transistor Q6 are respectively the transistor Q5.
5 has a negative value whose absolute value is equal to the emitter voltage and the collector voltage of No. 5. The collector voltage of the two transistors Q5 and Q6 is, for example, the current amplifier A4 provided in the next stage.
It is adapted to be supplied as a base voltage to the front driver transistors Q7 and Q8 of a and A4b.

When the base current is supplied to the transistors Q7 and Q8, -V is supplied from the + Vcc power source through the transistor Q7, the common emitter resistor R11 and the transistor Q8.
A constant idling current flows to the cc power supply, and a positive voltage is generated at the emitter of the transistor Q7. A negative voltage whose absolute value is equal to the emitter voltage of the transistor Q7 is generated at the emitter of the transistor Q8.

The emitter voltages of the transistors Q7 and Q8 are supplied to the current amplifying transistors Q9 and Q10 as base voltages, respectively.
As a result, a constant idling current flows from the + Vcc power supply to the -Vcc power supply through the two emitter resistors R12 and R13 having the same resistance as the transistor Q9 and the transistor Q10.

Thus, if the idling current is made to flow when there is no signal, the transistors forming a pair in each stage start operating from the potential due to the idling current when a signal is input, so the dead time for the input signal is reduced. It disappears and is fast. Further, since the output of each stage changes from a negative level to a positive level, or when the output changes from a positive level to a negative level, amplitude distortion such as zero-cross distortion does not occur, so that linearity is also good.

Here, in the voltage amplifiers A3a and A3b, the bases of the transistors Q5 and Q6 are connected to a common wiring (-), respectively, via capacitors C2 and C3 having the same capacitance value, respectively. C2
The voltage dividing resistor R8, the capacitor C3, and the voltage dividing resistor R10 form two high-pass filters FLa and FLb having the same cutoff frequency.

The portions of the high-pass filters FLa and FLb in FIG. 2 are extracted and shown in FIG. 3, and the input voltage (divided voltage) thereof is shown.
The level of the output voltage _{V R2'} Filters for V _R2 shown in FIG. 3 (B). When the cutoff frequency of this high-pass filter is fc, fc = 1 / 2πC2R8 = 1 / 2πC3R10.

According to FIG. 3, in the band where the frequency of the input voltage Vi is lower than the cut-off frequency fc, the output voltage V _R2 ′ of the filter is smaller than the _divided voltage V _R2 , and the magnitude thereof is -20 dB / dec depending on the frequency. It is on any point of the characteristic line that slopes at. Therefore, the divided voltage V _R2
Is added to the bases of the transistors Q2 and Q4, and its filter output _{VR2 '} is added to the bases of the transistors Q5 and Q6, but it can be regarded that the transistors Q5 and Q6 are not substantially affected. Therefore, the voltage amplifiers A3a and A3b receive the outputs from the differential amplifiers A2a and A2b on the emitter sides of the transistors Q5 and Q6, and operate in cascade with respect to the differential amplifiers A4a and A4b. Operates following.

In the band where the frequency of the input voltage Vi is higher than the cutoff frequency fc of the high pass filter, the divided voltage V
The magnitude of _R2 and the output voltage V _{R2 '} of the filter become equal, and the _divided voltage V _R2 is applied to both the differential amplifiers A2a and A2b and the voltage amplifiers A3a and A3b.

In this case, if the voltage gain of the differential amplifiers A2a and A2b is 1 (0 dB) or more, the silane transistor Q5
In Q6 and Q6, the voltage applied from the differential amplifier to the emitter side is larger than the divided voltage V _R2 directly applied to the base, so that the operation is governed by the input voltage on the emitter side. Therefore, similar to the above, the voltage amplifiers A3a and A3b are
Operates in cascade with respect to the differential amplifiers A2a and A2b,
The current amplifiers A4a and A4b are voltage amplifiers A3a and A3b.
Operates following.

However, the differential amplifiers A2a and A2b
When the voltage gain of is smaller than 1, the voltage applied from the differential amplifier to the emitter side becomes smaller than the voltage V _R2 applied directly to the base in the transistors Q5 and Q6.
The operation is dominated by the input voltage V _R2 on the base side. That is, in this case, the input voltage Vi is the capacitor C
1 is applied to the differential amplifier from the common wiring (+) and the divided voltage V _R2 is applied to the differential amplifier and the voltage amplifier from the common wiring (-). It is apparent that the divided voltage V _R2 bypasses the differential amplifier and is applied to the voltage amplifier since it does not contribute to the voltage amplifier. Therefore, the first operation unit is the voltage amplifier A3.
a, A3b, and the current amplifiers A4a, A4b operate following the voltage amplifier.

By the way, the voltage gain and the current gain of the transistor have a constant value from a direct current to a certain frequency in the alternating current region, and when the frequency is exceeded, it generally decreases at a rate of -20 dB / dec due to the distributed capacitance of the element itself. At the beginning, when the frequency becomes higher, the decrease will be gain 1 or 0.
reaches dB. The frequency at the gain of 0 dB is called the GB product or the transition frequency (f _T ),
In the case of a high frequency transistor, it is generally higher than that of a general-purpose IC amplifier, and has a value of, for example, several 10 MHz to several 100 MHz.

The relationship between the voltage gain and frequency of each unit shown in FIG. 2 is shown in FIG. Referring also to the figure, since the high-precision amplifier A1 uses the same IC element as the conventional device, the open-loop gain G1 thereof shows the characteristic of FIG. 7 as it is. Here, assuming that the frequency at which the actual open loop gain G1 becomes 0 dB is f2, the high pass filter FL
The cut-off frequency fc of a and FLb is set to a frequency substantially equal to f2, for example.

Now, assuming that the voltage Vi input to the device is a DC voltage or a low-frequency AC voltage whose frequency is f2 or less, the output voltage -Vc of the high precision amplifier A1 is a differential amplifier via the common wiring (+). Transistor Q1 of A2a and A2b
And the base of Q3, the divided voltage V of the input voltage Vi
_R2 opens the common wiring (-) and is added to the bases of the transistors Q2 and Q4 of the differential amplifier.

[0062] In this case, the absolute value of the output voltage -Vc of the high-precision amplifier A1 from the frequency greater than the voltage _{V R2} of the input voltage Vi, the collector of the transistor Q2 is current corresponding to the inversion voltage Vc of -Vc In addition to the idling current, the current flows from the + Vcc power supply, and a voltage change occurs due to the current increase in the resistor R5. In the transistor Q4, a current reduced from the idling current by a current corresponding to the inversion voltage Vc of -Vc is -V from the collector.
It flows out to the cc power supply, and a voltage change occurs in the resistor R7 due to a decrease in current.

Here, for example, the ratio of the voltage change generated in the resistor R5 and the inversion voltage Vc (absolute value) in the transistor Q2, that is, the voltage change / Vc of the resistor R5 is taken as the voltage gain of the differential amplifier A2a. Similarly, the resistance R
If the ratio of the voltage change occurring in the transistor 7 and the inversion voltage Vc (absolute value) in the transistor Q4, that is, the voltage change / Vc of the resistor R7 is taken as the voltage gain of the differential amplifier A2b, the two voltage gains become equal. . Now, the differential amplifiers A2a and A2b
G2 is a constant gain of 30 dB from DC to frequency f3 in the AC region, and G2 decreases at a rate of −20 dB / dec in a frequency band higher than f3, and G2 is 0 dB at frequency f5, that is, An example where the gain is 1 is shown in FIG.

By the way, the currents flowing in the transistors Q2 and Q4 of the differential amplifiers A2a and A2b are changed to change the resistance R5.
When a voltage change occurs between R7 and R7, voltage amplifiers A3a and A3
In b, the current flowing from the transistor Q5 to the transistor Q6 via the diodes D1 to D4 also changes. Here, when the frequency of the input voltage Vi is lower than the cutoff frequency fc of the high pass filters FLa and FLb, it can be considered that the transistors Q5 and Q6 operate in the grounded base type.

In this case, assuming that the voltage gain of the transistors Q5 and Q6 is the ratio of the output voltage change on the collector side to the input voltage change on the emitter side, the input voltage change of the transistor Q5 is the input impedance of Q5 × the emitter current change amount. The output voltage change on the collector side is the ON resistance of the diodes D1 and D2 times the collector current change. In this case, since the base current of the transistor Q5 is extremely small and the change in the emitter current = the change in the collector current is ignored, the voltage gain of the transistor Q5 becomes the ON resistance of the diodes D1 and D2 / the input impedance of Q5.

Since the transistor Q6 is similar to the transistor Q5, its voltage gain can be set to ON resistance of the diodes D3 and D4 / input impedance of Q6. Therefore, the voltage amplifiers A3a and A3b
Let G3 be the overall gain of G3: G3 = ON resistance of D1 and D2 / input impedance of Q5 + ON resistance of D3 and D4 / impedance of Q6.

Now, assuming that the on resistances of the diodes D1 to D4 are equal and the input impedances of the transistors Q5 and Q6 are also equal, the overall gain G3 is G3 = 4 ×.
It becomes the ON resistance of the diode / the input impedance of Q5 (Q6). Here, the input impedance of the grounded base transistor is generally low, about several tens of Ω, and the on-resistance of the diode depends on the magnitude of the idling current, but in the small current near the rise of the current, it is about several hundred Ω or several times thereof. is there.

Therefore, the overall gain G3 of the voltage amplifiers A3a and A3b is constant at 40 dB from the DC to the frequency f4 in the AC region, and G3 is -20 d in the band higher than f4.
FIG. 4 shows an example in which G3 becomes 0 dB, that is, gain 1 at the frequency f7, which decreases at the ratio of B / dec. The current amplifiers A4a and A4b are voltage amplifiers A3a and A4a.
Although the circuit operates in a cascaded manner with respect to 3b, it is not shown because the circuit is a collector grounded type and the voltage gain is 1 (0 dB).

2 and 4, the high-precision amplifier A1 is used when the input voltage Vi is from DC to frequency f1 in the AC region.
The differential amplifiers A2a and A2b and the voltage amplifier A3
a and A3b operate in cascade, and their open loop total gain G
1 + G2 + G3 is, for example, 170d as shown by the chain line.
B is constant. Here, f1 is the frequency at which the gain G1 of the high-precision amplifier A1 made of an IC element begins to decrease as in the conventional device.

In the frequency band from f1 to f2, the above three units operate in cascade, but the open loop gain G1 of the precision amplifier A1 decreases at a rate of -40 dB / dec, and at the frequency f2. The gain reaches 1 (0 dB). Therefore, the open loop total gain G1 + G2 + G3
Also decreases at the same rate, and the total gain at frequency f2 is G
At 2 + G3, the value is 70 dB, for example.

Here, the high-pass filters FLa and F
The cut-off frequency fc of Lb is set to, for example, the high precision amplifier A1.
If the frequency is set to be approximately equal to the frequency f2 at which the open-loop gain G1 of 0 is 0 dB, the frequency of the input voltage Vi becomes f2.
In the higher band, the divided voltage V _R2 applied to the bases of the transistors Q2 and Q4 of the differential amplifiers A2a and A2b via the common wiring (-) is applied to the voltage amplifiers A3a and A3b.
Will also be added to the bases of the transistors Q5 and Q6. However, in the band where the frequency is higher than f2, the gain of the high-precision amplifier A1 becomes smaller than 1, so that the-input terminal does not become an imaginary short circuit with the + input terminal. Therefore, the input voltage Vi is not divided by the resistors R1 and R2,
It can be considered that the divided voltage V _R2 has the same magnitude as the input voltage Vi.

In the transistors Q5 and Q6 of the voltage amplifiers A3a and A3b, a differential output voltage higher than the divided voltage V _R2 applied to the base side by G2 times (for example, 30 dB) is higher than that on the emitter side. Motion amplifier A2
a and A2b. Therefore, the operations of the transistors Q5 and Q6 are controlled by the input voltage on the emitter side, and in the band where the frequency is higher than f2, the differential amplifiers A2a and A2b are the leading operation units, and the voltage amplifiers A3a and A3b.
Operates continuously to the differential amplifier.

The range in which the voltage amplifier cascades with the differential amplifier is the band from the frequency f2 to the frequency f5 at which the gain G2 of the differential amplifier reaches 0 dB. The open loop total gain G2 + G3 of both amplifiers in this range is constant at, for example, 70 dB from the frequency f2 to the frequency f3 at which the gain G2 of the differential amplifier begins to decrease as shown by the alternate long and short dash line.
In the band up to the frequency f4 where the gain G3 of the voltage amplifier begins to decrease beyond f3, the total gain decreases at a rate of -20 dB / dec.

In the frequency band from f4 to f5, the gain G3 of the voltage amplifier has a decrease characteristic of -20 dB / dec, so that the open loop total gain G2 + G3 of the differential amplifier and the voltage amplifier is -40 dB / It decreases at the rate of dec. Further, in the band where the frequency exceeds f5, the gain G2 of the differential amplifier is 1 or less and does not contribute to the amplification of the signal. Therefore, the voltage amplifier becomes the first operation unit for the input voltage, and the current amplifier follows the voltage amplifier. And work.
In this case, the total voltage gain of the open loop becomes the gain of the voltage amplifier itself and decreases along G3 at a rate of -20 dB / dec.

The frequency of the input voltage is f
In the band higher than 5, the voltage amplifiers A3a, A3b
Although the transistors Q5 and Q6 of the above-mentioned operate in a grounded-emitter type, the gain G3 thereof is about the same as that in the case of grounded-base type. The current amplifiers A4a and A4b are composed of individual components as described above, and their currents are several tens.
Since the impedance is set to a low impedance of Ω or less, it is sufficiently possible to make the value of current gain × bandwidth approximately equal to the GB product of the voltage amplifiers A3a and A3b.

Here, when the closed loop gain G of the entire device is set to 10 dB as in the conventional example of FIG. 7 and shown by a broken line in FIG. 4, the open loop gain G of the voltage amplifiers A3a and A3b is shown.
3 is a line that decreases at a rate of -20 dB / dec and the above 1
The frequency f6 at the intersection with the 0 dB line is the bandwidth of this device. In this example, it can be seen that the upper limit frequency of the bandwidth is higher than the conventional example by one digit or more.

[0077]

As described above, according to the present invention, a differential amplifier operating in cascade with respect to a high precision amplifier,
The voltage amplifier, current amplifier, etc. are each composed of individual parts, and two systems are symmetrically paired to the positive and negative sides with respect to the zero potential when there is no signal, and a wide band and low distortion are achieved. In addition to the above, an input signal having a frequency higher than the frequency at which the voltage gain of the differential amplifier, which is a relatively low speed, among the three units configured by the above-mentioned individual components is higher than 1 is bypassed by the high-pass filter and the voltage is input. Join the amplification,
The voltage amplifier and the current amplifier operate in cascade. Therefore, according to the present invention, the upper limit value of the frequency range in which the device can operate can be expanded to the bandwidth of the voltage amplifier, and the amplitude distortion is small, so that the linearity is also good.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a basic electrical configuration of the present invention.

FIG. 2 is an equivalent circuit diagram of a main part of an electrical configuration according to the present invention.

FIG. 3 is a configuration diagram of a high-pass filter according to the present invention and a characteristic explanatory diagram of the high-pass filter.

FIG. 4 is an explanatory diagram of a gain characteristic of each unit according to the present invention.

FIG. 5 is a block diagram showing an electrical configuration of a conventional device and an operation explanatory diagram thereof.

FIG. 6 is an operation explanatory diagram of a conventional device.

FIG. 7 is an explanatory diagram of a gain characteristic of each unit in the conventional device.

FIG. 8 is an operation explanatory diagram of a conventional device.

[Explanation of symbols]

 A1 DC high-precision amplifier A2a, A2b Differential amplifier A3a, A3b Voltage amplifier A4a, A4b Current amplifier C1 Feedback capacitor C2, C3 High-pass filter capacitor D1-D4 Diode FLa, FLb High-pass filter Q1-Q6 Transistor R4-R10 Resistor Vi input Signal-Vc Negative feedback voltage

Claims (6)

[Claims] 1. A DC high-precision amplifier having two input terminals, one terminal of which is grounded, an input signal is applied to the other terminal, and the other terminal of the DC high-precision amplifier is passed through a feedback circuit including a capacitor from the output terminal of the same. While sending a negative feedback voltage to the terminal of, the feedback voltage and the input signal are applied to the differential amplifier, the output voltage of the difference is amplified by the voltage amplifier, and then converted into the current by the current amplifier to drive the load. In a composite wide-band amplifier that obtains an output, the feedback voltage sent from the DC high-precision amplifier is received at each one input terminal, and the input signal is received at each other input terminal and the difference voltage is amplified. And a second differential amplifier for receiving the output of the first differential amplifier at one input terminal and the other input of the input signal through the first high-pass filter. The input of the second differential amplifier to another input terminal and the input signal to the other input terminal via the second high-pass filter. First and second voltage amplifiers that amplify the output of the differential amplifier or the input signal that has passed through the high-pass filter depending on the level of the input signal frequency with respect to the cutoff frequency, and the outputs of the first and second voltage amplifiers. And a first current amplifier and a second current amplifier which respectively receive and convert the current into a current, and output the current. 2. The first differential amplifier forms a pair of two NPN type transistors, the emitters of both transistors are connected to a negative power supply voltage path through a common resistor, and the collector of one transistor is positive. Is connected to the output voltage side of the DC high-precision amplifier as a receiving terminal for the feedback voltage, and the collector of the other transistor has the collector through a load resistor for generating a differential voltage. In addition to being connected to the positive power supply voltage path, the base side of the transistor is connected to the other input terminal side of the DC high-precision amplifier as a receiving terminal for the input signal. 2. The hybrid broadband amplifier according to claim 1, wherein an equal constant collector current is passed as an idling current. 3. The second differential amplifier forms a pair of two PNP type transistors, the emitters of both transistors are connected to the positive power supply voltage path through a common resistor, and the collector of one transistor is It is connected to the negative power supply voltage path, its base side is connected to the output terminal side of the DC precision amplifier as a receiving terminal of the feedback voltage, and the collector of the other transistor is through a load resistor for generating a differential voltage. Is connected to the negative power supply voltage path and the base side of the transistor is connected to the other input terminal of the DC high precision amplifier as a receiving terminal for the input signal. 2. The hybrid wide band amplifier according to claim 1, wherein a constant collector current substantially equal to that of the transistor is passed as an idling current. 4. The first voltage amplifier includes a PNP transistor and a plurality of diodes, the emitter of the transistor being connected to the collector side of the other transistor of the first differential amplifier to have the same collector voltage. At the same potential, the plurality of diodes are connected in series in the forward direction on the collector side of the PNP transistor, and a positive base voltage is applied to the base of the transistor, so that the second voltage amplifier is provided. Includes an NPN type transistor and a plurality of diodes, the emitter of the transistor is connected to the collector side of the other transistor of the second differential amplifier to have the same potential as the collector voltage, and the collector of the NPN type transistor is connected. On the side, the plurality of diodes are connected in series and in the forward direction with the diodes of the first voltage amplifier. At the same time, a negative voltage whose absolute value is equal to the base voltage applied to the PNP transistor of the first voltage amplifier is applied to the base of the NPN transistor, and when there is no signal, the transistor of the first voltage amplifier operates. 2. The composite wide band amplifier according to claim 1, wherein a constant collector current is made to flow as an idling current to the transistor of the second voltage amplifier through the group of diodes connected in series. 5. A first resistance, a second resistance for dividing the voltage between the two power supply paths into three, and a first resistance having the same resistance value as the first resistance, between the positive power supply voltage path and the negative power supply voltage path. Three of the three resistors are connected in series, and the common connection point of the first and second resistors is connected to the base of the transistor constituting the first voltage amplifier to supply a positive base voltage to the transistor. The common connection point is connected to the other input terminal of the DC high-precision amplifier via a capacitor, and the capacitor and the first resistor form a first high-pass filter for an input signal. The composite wide band amplifier according to claim 1. 6. The common connection point of the second and third resistors among the three resistors that divide the voltage between the positive power source voltage path and the negative power source voltage path into three parts constitutes the second voltage amplifier. Is connected to the base of the transistor to supply a negative base voltage to the transistor, and the common connection point has the same capacitance as the capacitor forming the first high-pass filter, and the DC high-precision amplifier 2. The composite wide band amplifier according to claim 1, further comprising a second high-pass filter connected to the other input terminal of the capacitor, the capacitor and the third resistor forming a second high-pass filter for an input signal.