JPS60167507A - Amplifier circuit - Google Patents

Abstract

PURPOSE:To attain the offset of a low level with no deterioration nor variation of characteristics of an amplifier circuit, by setting the coefficient of a circuit to be trimmed at a point excepting a signal route. CONSTITUTION:The bias currents I1 and I2 of a buffer circuit are controlled individually, and the base-emitter voltages of TRs Q3 and Q4 change individually in response to the values of the I1 and I2. Thus the I1 and I2 flowing to the TRs Q1 and Q2 of a differential amplifier circuit are controlled and well balanced to each other by selecting properly a trimming element which should undergo the destruction/conduction. In other words, the offset can be cancelled. In this case, the elements for trimming, i.e., many resistances R11-, R21- and trimming elements D11- and D21- are provided to a bias circuit which is set out of a signal path. Thus the time constants parasitic to those elements give no evil effects at all to the characteristics especially the frequency characteristics of the amplifier circuit.

Description

[Detailed Description of the Invention] [Technical Field] The present invention relates to an amplifier circuit technology and a technology that is particularly effective when applied to a differential amplifier circuit. This article relates to effective technology that can be used to achieve wideband low-off-cut (low-off-line) performance.

[Background technology]

The present inventor has developed and studied the following techniques regarding amplifier circuit technology, particularly circuit technology for wideband low-offset amplifiers.

That is, by trimming a part of the circuit constants of the differential amplifier circuit, offset and distortion are adjusted, thereby making the offset and lead as small as possible.

This will be explained in more detail below.

FIG. 1 shows an amplifier circuit studied prior to the present invention. The amplifier circuit shown in the figure includes a pair of bipolar transistors Ql that are differentially connected to each other.

Q2, this pair of transistors Q1. Q2σ) Constant current circuit l connected between the common emitter and the negative side power supply Vee
A load resistor Ru connected between the collector of O1 and each transistor Ql, Q2 and the positive power supply VCC.
It is composed of rx etc. and.

A differential input between the bases of both transistors Ql and Q2 is input to IN field 1. INH is introduced, and differential power 0UTH-1,0UTH is taken out from its collector.

Here, the collector load resistance RO is provided with a circuit constant whose value is adjusted by trimming. This circuit constant consists of a large number of resistors R11 to R14, R21, respectively.
~R24 and trimming elements D11-D14. D21
~D24, and by destroying any trimming element and making it conductive, the transistors Ql and Q2 are
By trimming the load resistance of the differential amplifier circuit, it is possible to cancel the off-set (DC offset voltage) of the differential amplifier circuit.

However, in this technique, since the circuit constant to be trimmed is provided in the signal path of the differential amplifier circuit, the characteristics of the differential amplifier circuit are affected by time constants such as capacitance parasitic to the circuit constant.

In particular, the frequency characteristics in the high range deteriorate. The inventor of the present invention has clearly determined that this problem arises. %, since the circuit constant to be trimmed is formed by connecting a large number of resistors and trimming elements as described above, the parasitic time constant inevitably becomes large. Therefore, when attempting to achieve a low offset by trimming, the trade-off arises in that the frequency characteristics in the high range are greatly degraded by the above-mentioned time constant. Furthermore, if the circuit constant to be trimmed forms part of the 517 load resistance as described above,
Off top 1. The inventor has also clarified that the load resistance value changes due to trimming to reduce the output voltage, which causes the problem that the expected output level or characteristics such as gain cannot be obtained. Ta.

[Purpose of the invention]

An object of the present invention is to provide an amplifier circuit technology that can realize a low offset without deteriorating or changing characteristics.

The above and other objects and novel features of the present invention will become apparent from the description of this specification and the accompanying drawings.

[Summary of the invention]

A brief overview of typical inventions disclosed in this application is as follows.

That is, by providing the circuit constants to be trimmed outside the signal path, a low offset can be realized without deterioration or change in characteristics. This goal is achieved.

〔Example〕

Hereinafter, typical embodiments of the present invention will be described with reference to the drawings.

In one drawing, the same or corresponding parts are indicated by the same reference numerals.

FIG. 2 shows an embodiment of a differential amplifier circuit according to the present invention.

First, the amplifier circuit shown in the figure is used as a head amplifier of an optical disk device, and is formed as a circuit within a semiconductor integrated circuit device.

The amplifier circuit shown in the figure is configured to be adjusted off by including a circuit constant to be trimmed, and the circuit constant is set to an offset value of the amplifier circuit at a point other than the signal path of the amplifier circuit. It is designed to be involved in Furthermore, a voltage feedback type Baduf Too path with a suction type constant current circuit as a load is connected to the differential input IN old and IN1-3 sides of the above amplifier circuit, respectively, and the circuit constant that determines the bias current of the sofa circuit is It's time to trim it.

Here, the main parts of the differential amplifier circuit are a pair of bipolar transistors Q1 . Q2, the pair of transistors Ql, the common emitter of Q2, a constant current circuit 0 connected between the ivy and the negative power supply Vee, and each transistor Ql.

It is composed of load resistors Rθ and the like connected between the collector of Q2 and the positive power supply Vcc.

Both transistors Q1. The base differential input lNl-1-1, INS of Q2 is introduced, and the VC is set such that the differential output OUT, 0UTt-1 is taken out from its collector.

That's too sweet.'' The sofa circuit consists of an emitter follower using a so-called bipolar transistor. This buffer circuit is for each person's power field 1. It is established for each IN day. The buffer circuit, which is input to one side of the IN input terminal, has a bipolar transistor Q3. Q5. Emitter resistance Re,) a large number of resistors R11 to R14 and trimming elements DIl to D1 to form circuit constants to be trimmed
Consisting of 4. Similarly, the bias circuit on the other input INH side includes bipolar transistors Q4. Q6. It is composed of an emitter, a vine resistor Re, a large number of resistors R21 to form a circuit constant to be trimmed, and a trimming element D21-. Here, transistor Q5. Q6 each has an emitter follower.

Further, transistors Q5 and Q6 each have a predetermined current If by applying a constant control voltage vb to their bases.
, a constant 1 that sucks I2! form a flow circuit. The trimming elements D11~. As for D21~.

A diode (or bipolar transistor) is used that is destroyed by external energization and becomes 4 conductive. Each trimming element D11~.

D21-- are each connected in series with a resistor whose resistance value is weighted with a predetermined value, and this series circuit is connected in parallel with the emitter and inter-resistor ReVc, respectively.

By selecting an arbitrary trimming element and causing it to become conductive, the value of the resistor connected in parallel to the emitter resistor BeK can be adjusted, that is, trimmed. As a result, the current I flowing through the constant current circuit is
t, I2j, that is, the bias current of the Bavva circuit can be adjusted individually.

As described above, the bias current I of the above-mentioned buffer circuit is
By adjusting I and I2 individually, the bias current 11.
With the change in I2, transistor Q3. Q4 pace・
The emitter voltage changes individually. As a result, destruction #4
Transistor Q1. of the differential amplifier circuit can be passed by appropriately selecting the transistor Q1. The bias currents fi11 and I2 flowing through Q2 can be individually adjusted to balance each other. In other words, the offset can be moderately offset.

According to the above 5KI, it is possible to perform trimming to cancel the offset/situation.What should be noted here is the elements for performing the trimming, that is, the large number of resistors R11~, R21~ and the trimming. Elements D11~. This means that D21~ are provided in the bias circuit outside the signal path. Because of this K, the time constants parasitic to the large number of elements do not have any adverse effect on the characteristics of the amplifier circuit, especially the frequency characteristics. Further, since the trimming for canceling the offset can be performed nine times without changing the load resistance RO, there is almost no possibility that the output level or gain of the amplifier circuit will change due to the trimming. Therefore, it is possible to obtain an amplifier circuit that has good frequency characteristics in the high range and stable output level, gain, etc. For this reason, the optical disc device
You can get an excellent amplifier.

〔effect〕

C1) Including a circuit constant to be trimmed.In a differential amplifier circuit configured to be adjusted offset from K. By providing the value 5 to be related to the offset value, it is possible to achieve the effect of realizing low offset and shading without deterioration or change in characteristics.

Although the invention made by the present inventor has been specifically explained above based on examples, this invention is not limited to the above examples, and it is understood that various changes can be made without departing from the gist of the invention. Needless to say. For example, the trimming element may be of the breaking-breaking type. Also,
The transistors Ql-Q6 and the like may be MO8 elements.

[Application field]

The above explanation has mainly been about the application of the invention made by the present inventor to an amplifier circuit used as a head amplifier of an optical disk device, which is the field of application in which the invention was made, but the invention is not limited to this. For example, to 1. of a magnetic disk device. It can also be applied to J-dump technology.

At least it can be applied to conditions that require Offset adjustment.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing an amplifier circuit studied prior to the present invention. FIG. 2 is a circuit diagram showing an embodiment of the amplifier circuit according to the present invention. Ql, Q2. Q3. Q4. Q5. Q6...active element (
bipolar transistor), IO...constant current circuit, I
f, I2...bias current, RO...load resistance, R
11-R14, R21-R24...Circuit constant (resistance) to be trimmed, Re...Emi, vine resistance, DIl
~D14. D21-D24...trimming element, IN
f-H, INH...Differential input, 0UTH-1,0UT
H...differential output, Vcc, Vee...power supply, V
b...Control voltage. (Representative Patent Attorney Akio Takahashi - αυ Figure 1). e a Second Figure 1/e.

Claims (1)

[Claims] 1. A differential amplifier circuit configured to be offset adjusted by including a circuit constant to be trimmed, wherein the circuit constant is connected to a signal path other than the signal path of the amplifier circuit. By the way, an amplifier circuit characterized in that it is provided so as to be involved in an off-set value of the amplifier circuit. 2. A voltage feedback type buffer circuit with a suction type constant current circuit as a load is provided on the differential input side of each of the above amplifier circuits,
2. The amplifier circuit according to claim 1, wherein a circuit constant determining a bias current of the buffer circuit and the amplifier circuit is trimmed.