JPS61144107A - Amplifier - Google Patents

Abstract

PURPOSE:To prevent deterioration in linearity due to an output current by providing the 2nd amplifier whose output current gain is set so that the voltage connected with a specific load is the same as that of the 1st amplifier. CONSTITUTION:An output current I of a current output amplifier 4 is expressed as I=Vi.gm, where Vi is an input voltage and (gm) is a gain of a current output amplifier 4. In connecting a load having an impedance Zl to an output terminal 2, a voltage Vo' generated across the load by the output current I of the current output amplifier 4 is expressed as Vo'=Vi.gm.Zl. On the other hand, the relation of Vo=G.Vi, where G is the gain of a voltage output amplifier 3. Thus, the relation of Vo=Vo' is obtained by selecting (gm) as gm=G/Zl and the current to the load is supplied from the current output amplifier.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an amplifier with reduced voltage distortion of output power.

2. Description of the Related Art In recent years, the output voltage distortion factor of amplifiers that control the output voltage by negative feedback has been significantly reduced by various technological developments. However, distortion is not completely zero, and distortion of the output voltage often becomes a problem, especially in amplifiers that require power supply to a load, because the linearity of the output stage through which a large current flows is poor. A conventional amplifier will be explained below.

FIG. 4 shows an example of a conventional amplifier. 1 is an input terminal, 2 is an output terminal, 6 is a pre-stage amplifier, 7 is a pre-driver transistor, 8 is a single end-of-nox pull (hereinafter referred to as 5xpp) output stage, 9 is a negative feedback circuit that negatively feeds back the output voltage, 10 is a phase compensation circuit.

The gain G of this configuration is 1+Mutom 2·β. Here, Al is the gain of the pre-stage amplifier 6, M2 is the gain from the pre-driver transistor 7 to the 5xpp output stage, the emitter resistance of the pre-driver transistor 7 is r, and the impedance of the phase compensation circuit 10 is z, s.
The current amplification factor of the gpp output stage is hf'e.

When the impedance of the load connected to the output terminal 2 is 2, it becomes re.

Moreover, the open-loop transfer characteristic of this configuration is as follows. Here, TI and T4 are the time constants of the negative feedback circuit 9, and T
2 is the time constant of the pre-stage amplifier 6, T3 is the time constant of the phase compensation circuit 10, T5. Ti
>To・T2 >To・T3>To・T4<To
, Ts< To・T6 (T□).

Problems to be Solved by the Invention In this conventional configuration, the current supplied to the load is 5K.
Flows through the PP output stage. The current amplification factor tlfa of the 5xpp output stage generally tends to decrease as the current increases. For this reason, hf when the output amplitude is small current and large current is
e changes, the gain m2 becomes non-linear, and distortion occurs.

In addition, in order to increase the distortion improvement effect due to negative feedback, ω
. The larger is better, but since T5+T6 also becomes large in a large current region, ω0 is limited, and the distortion improvement effect by negative feedback in a high frequency region becomes small.

The present invention has been made in view of the above problems, and an object of the present invention is to provide an amplifier that prevents deterioration of linearity due to output current and improves the distortion improvement effect due to negative feedback in a high frequency region.

Means for Solving the Problem In order to solve the above problem, the present invention provides a first amplifier with voltage input and voltage output, and a voltage gain that is equal to that of the first amplifier when a specific load is connected with voltage input and current output. It has a second amplifier whose output current gain is set so that the gain of the output current is set such that the input and output of the first amplifier and the second amplifier are connected in parallel.

Operation The present invention uses the above-described configuration to output the output current supplied to the load from the current output amplifier, thereby reducing the load on the voltage output amplifier. Therefore, the linearity of the output stage of the voltage output amplifier is improved, negative feedback can be stably provided up to a high frequency region, and output voltage distortion can be significantly reduced.

Embodiment FIG. 1 is a block diagram showing a first embodiment of the amplifier of the present invention. In FIG. 1, 1 is an input terminal, 2 is an output terminal, 3 is a voltage output amplifier, and 4 is a current output amplifier.

In the amplifier configured as described above, the output current of the current output amplifier 4 is such that the input voltage is vi, and the current output amplifier 4
When the gain of is expressed as I = Vi -its. When a load with an impedance zL is connected to the output terminal 2, the voltage voltage generated across the load by the output current of the current output amplifier 4 becomes vo=impedance.zL-='ii-gm-ZL. On the other hand, when the gain of the voltage output amplifier 3 is G,
The voltage Vo output to the output terminal 2 is To = G
-Vi. Therefore 1,! By setting i'm = G/ZL, v0 = vo', current is supplied to the load by the current output amplifier, and the output stage of the voltage output amplifier can control the output voltage without supplying current.

As described above, according to this embodiment, by connecting the current output amplifier whose gain is equalized for a specific load in parallel with the voltage output amplifier, the output stage of the voltage output amplifier has a current supplied to the load. Therefore, the linearity of the output stage of the voltage output amplifier is improved, and the time constant of the output stage is also reduced, so that the degree of improvement in high-frequency distortion due to negative feedback is also improved.

Furthermore, by simply passing a small amount of bias current through the output stage of the voltage output amplifier, the output stage of the voltage output amplifier can be operated in class A mode.

FIG. 2 is a configuration diagram of a second embodiment of the present invention, in which the voltage output amplifier 3 is configured by negative feedback to the differential input 5KPP output amplifier 31 through resistors 32 and 33, and the current output amplifier 3 is 4 is configured by negative feedback to an amplifier 41 with differential input and 5xpp output through an operational amplifier 42 and resistors 43 to 47.

Here, the gains of the differential input 5xpp output amplifier 31, 41 and operational amplifier 42 are each infinitely large,
Furthermore, resistors 32, 33, and 43 to 47 are R32, respectively.
Assuming R33 and R43 to R47, the voltage output amplifier gain G is G=(R32+R33)/R32. Also, the current output amplifier gain 9rtr is R44/R
43=R46/R47, then ゛. Therefore, when the load impedance is Z, if each resistance value is set to be (R32-1-133)/R32, then G = gm -Z
This makes it possible to prevent the load current from flowing through the output stage of the voltage output amplifier 3.

As described above, by configuring a current output amplifier with a negative feedback circuit using resistors and an operational amplifier, it is possible to
A pp output amplifier can be easily converted into a current output amplifier.

FIG. 3 shows a third embodiment of the present invention, in which 1 to 4 are the same components as in the first embodiment of FIG. 1, and 5 is a frequency characteristic equalizing amplifier. That is, in this embodiment, by connecting the frequency characteristic equalizing amplifier 6 to the input of the current output amplifier 4, it is possible to give the current output amplifier gain an arbitrary frequency characteristic.

As described above, by connecting a frequency characteristic equalizing amplifier to the input of the current output amplifier and giving the gain of the current output amplifier an arbitrary frequency characteristic, even if the impedance of the connected load changes with frequency ( ,=gm-
It is possible to realize Z.

Effects of the Invention As described above, the present invention improves the linearity of the output stage of the voltage output amplifier by connecting the current output amplifier whose gain is equalized for a specific load in parallel with the voltage output amplifier. Negative feedback can also improve high-frequency distortion improvement.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the configuration of an amplifier according to a first embodiment of the present invention, FIG. 2 is a block diagram of a second embodiment of the present invention, and FIG. 3 is a block diagram of a third embodiment of the present invention. FIG. 4 is a block diagram showing the configuration of a conventional amplifier. 1...Input terminal, 2...Output terminal, 3
. . . Voltage output amplifier, 4 . . . Current output amplifier, 5 . . . Frequency characteristic equalization amplifier. Name of agent: Patent attorney Toshio Nakao and 1 other person No. 1
Figure 341, pressure output amplifier 4t, outflow or beak width

Claims (2)

[Claims] (1) A first amplifier with voltage input and voltage output, and a second amplifier with the output current gain set so that the voltage gain when a specific load is connected with voltage input and current output is the same as that of the first amplifier. an amplifier in which the input and output of a first amplifier and a second amplifier are respectively connected in parallel. (2) The amplifier according to claim 1, wherein the gain of the second amplifier is varied depending on the frequency.