JPS6314302A - Recording circuit - Google Patents

Abstract

PURPOSE:To facilitate the adjustment by supplying a recording signal inputted from a rotary transformer to a differential amplifier circuit applying linear differential amplification via an input circuit having a low input impedance so as to produce a recording current thereby spreading a low cut-off frequency. CONSTITUTION:An effective input impedance Rin of a recording circuit RK viewed from a secondary winding of a rotary transformer RT shows a practi cally sufficiently low impedance because common-base amplifier circuits BE1, BE2 and negative feedback circuits NF1, NF2 are provided in an input circuit section. Thus, the cut-off frequency fL at a low frequency when viewed from the signal source toward the rotary transfer RT is remarkably reduced and the frequency band of recording information recorded by a recording head is expanded. Further, since the differential amplifier circuit AMP applies linear differential operation, the recording circuit RK is adjusted while the recording current is changed gradually at the adjustment of the recording circuit RK and the adjustment is facilitated.

Description

[Detailed description of the invention] The present invention will be explained in the following order.

A. Industrial field of application B. Overview of the invention C. Conventional technology Problems to be solved by the invention E. Means for solving the problems (Fig. 1) F. Effects (Fig. 1)
Embodiment (FIGS. 1 to 3) G Embodiment (FIGS. 1 to 3) H Effects of the invention This can be applied when recording on a recording medium using a rotating head.

B. Summary of the Invention The present invention provides a recording circuit that amplifies a recording signal manually inputted from a rotary transformer to generate a recording current for a recording head, in which the recording signal manually inputted from the rotary transformer is amplified by a low input impedance. By supplying a recording current to a differential amplifier circuit that linearly performs differential amplification operation through an input circuit with a The circuit can be realized.

C. Prior art In conventional DVTRs, a recording amplifier circuit is provided on the non-rotating lower drum side, and the recording current is sufficiently amplified in the recording amplifier circuit, similar to the case of a video tape recorder (AVTR) that records and reproduces analog signals. A configuration in which the information is transmitted via a rotary transformer to a recording head mounted on a rotating upper drum is often used.

D Problems to be Solved by the Invention However, in a DVTR, the recording current to be sent out from the recording amplifier circuit actually has a much wider spectrum than in the case of analog signals, and the frequency of the pit clock is several tens [ From the upper limit band of M)lz), the emission line spectrum appears from tens to hundreds (kHz)
It is desirable to be able to amplify a wide frequency band that extends to the lower limit of the frequency band to a practically sufficient signal level.

However, when using a configuration in which the recording current amplified in the recording amplifier circuit is transmitted to the recording head via a rotary transformer, as in the conventional case, the cutoff frequency determined by the circuit constants of the rotary transformer , there is a problem that the bandwidth is limited.

As a method to solve this problem,
In No. 8, a recording amplification circuit is installed on the rotating upper drum side,
A configuration has been proposed in which a rectangular wave representing a digital signal is transmitted as recording information to the recording amplifier circuit from the fixed lower drum side via a rotary transformer.

However, according to this method, since the signal form of the recorded information supplied to the recording amplifier circuit is specified as a rectangular wave, by reproducing and monitoring the recorded information recorded on the recording medium via the recording head, When adjusting and confirming the characteristics of the recording circuit system, since it is not possible to adjust the linear recording signal level (because only the current corresponding to the logical "1" or "0" level can be passed), in reality the rotating drum is There is the inconvenience of having to temporarily stop the recording circuit system to adjust the recording circuit system.

The present invention has been made in consideration of the above points, and aims to propose a recording circuit that can linearly amplify recorded information and reliably amplify it up to the frequency of the lower limit band. .

E Means for Solving the Problem In order to solve this problem, the present invention provides a pair of differential amplification transistors Q1 and Q2, and a linear differential operation of the pair of differential amplification transistors Q1 and Q2. a differential amplifier circuit AMP that supplies a recording current to the recording head HR through a pair of differential amplifier transistors Q1 and Q2, and a base-grounded type that receives recording signals applied from a rotary transformer RT. Amplifier circuits BEI, BF2, and this base-grounded amplifier circuit BE
Negative feedback circuits NFL and NF2 having negative feedback transistors Q4 and Q6 that receive the outputs of I and BF2 at their bases and provide negative feedback to the input terminals of the grounded base amplifier circuits BEI and BF2;
and current mirror circuits MYI, MY2 that connect the bases of negative feedback transistors Q4, Q6 to one base of a pair of differential amplification transistors Ql, Q2, and record signals input from the rotary transformer RT. A pair of input circuits IN1 and IN2 are provided to generate a recording current in the differential amplification circuit AMP by inputting to the bases of the pair of differential amplification transistors Q1 and Q2, respectively.

Recording circuit R seen from the secondary winding side of F-action rotary transformer RT
The effective input impedance R1 of K becomes sufficiently low for practical use because the common base type amplifier circuits BEI, BH3 and the negative feedback circuits NFI, NF2 are provided in the input circuit section. By thus being able to further reduce the cutoff frequency fL in the low range when looking from the signal source to the rotary transformer RT side, it is possible to expand the frequency band of recording information that can be recorded by the recording head.

Furthermore, since the differential amplifier circuit AMP performs a linear differential operation, a recording current that changes linearly in response to changes in the recording signal input from the rotary transformer RT can be passed through the recording head HR, and thus the recording When adjusting the circuit RK, the recording circuit RK can be adjusted while gradually changing the recording current, thereby making it possible to obtain a recording circuit that is easy to adjust.

G Example The following drawings show the present invention as a digital VTR (1) V
An example in which the present invention is applied to TR) will be described in detail.

In FIG. 1, RK indicates the recording circuit as a whole, and is made of, for example, an NPN transistor, and has a pair of differential amplification transistors Q1 and Q2, each forming a differential pair, and the recording head HR is connected to the collector of the transistor. The differential amplifier circuit AMP includes a differential amplifier circuit AMP.

The emitters of transistors Q1 and Q2 are connected to the negative power supply line -1 through resistors R1 and R2, respectively, and a series circuit consisting of a resistor R3 and a DC cut capacitor C is connected between the emitters. A linear operation circuit LIN is configured to linearly differentially operate the differential amplifier circuit AMP with respect to the range of signal levels determined by the resistors R1 to R3.

Recording information supplied from the secondary winding N2 of the rotary transformer RT is applied to the bases of the pair of transistors Q1 and Q2 via input circuits INI and IN2, respectively.

One input circuit INI is connected to a common base circuit BEI made up of a PNP type transistor Q3 whose emitter is connected to one end of the secondary winding N2 of the rotary transformer RT. Here, the base of transistor Q3 is grounded,
The emitter is connected to the positive power line +V via a bias resistor R4, and the collector is connected to the negative power line -2 via a bias resistor R5.

In addition to this configuration, the input circuit INI includes a transistor Q
3, the collector of which is connected to the emitter of transistor Q3, and the emitter is connected to the negative power supply line -V via a load resistor R6. Thus, the negative feedback transistor Q4 constitutes a series negative feedback circuit, and when the recording signal applied from the rotary transformer via the transistor Q3 is generated at the collector of the transistor Q3,
This is negatively fed back to the emitter of the transistor Q3 via the base and collector of the transistor Q4.

The base of the negative feedback transistor Q4 is connected to the base of the differential amplification transistor Q1 by a current mirror circuit MVI.
In this way, a current having the same value as the current flowing through the load resistor R6 flows through the emitter of the transistor Q1.

The other input circuit IN2 has a completely symmetrical circuit configuration with the input circuit INI, and includes a common base circuit BE2 consisting of a transistor Q5 corresponding to the transistor Q3, and bias resistors R7 and R8 corresponding to the bias resistors R4 and R5. It also has a negative feedback circuit NF2 consisting of a transistor Q6 and a load resistor R9 corresponding to the transistor Q4 and the load resistor R6, and a transistor corresponding to the current mirror circuit MYI formed by connecting the bases of the transistors Q4 and Ql. It has a current mirror circuit MY2 in which the base of transistor Q6 is connected to the base of transistor Q2.

In the configuration shown in FIG. 1, the recorded information supplied between both ends Tl and T2 of the primary winding N1 of the rotary transformer RT is as follows:
It is induced in the secondary winding N2 and supplied to the emitters of transistors Q3 and Q5 of input circuits INI and IN2. At this time, the recording signal generated at the collectors of the transistors Q3 and Q5 is transferred to the negative feedback transistors Q4 and Q6.
The current is fed back to the emitters of transistors Q3 and Q5 through current mirror circuits MY1 and MY2, and current that matches the current flowing through load resistors R6 and R9 flows through differential amplification transistors Ql and Q2 through current mirror circuits MY1 and MY2. Control.

Thus, the differential amplification transistors Q1 and Q2 are controlled by the negative feedback transistors Q4 and Q6,
By performing a linear differential amplification operation via the linear operation circuit R3, a recording current generated by amplifying the recording information given to the rotary transformer RT to a predetermined current level is caused to flow to the recording head HR.

In this way, digital information at a predetermined recording level can be recorded on the recording medium that is in sliding contact with the recording head HR.

According to the configuration shown in FIG. 1, when the recording circuit RK performs a recording operation, the input impedance RL when looking at the input circuits INI and IN2 from the secondary winding LAN2 side of the rotary transformer RT is the transistor Q3 and Q5. The input impedance of the common base amplifier circuit BEI and BF2 is sufficiently low, and the common base amplifier circuit BEI
Based on the fact that negative feedback circuits NFL and NF2 are formed for RK and BF2, the value becomes sufficiently low, and as described below, the lower cutoff frequency fL of the recording circuit RK can be set to a practically sufficient value. low frequency (100 (kHz)
z ) or less).

First, when recording signal sources are connected to the input terminals T1 and T2 of the rotary transformer RT through amplifier circuits, the equivalent circuit around the rotary transformer R is
It can be represented as shown in the figure.

In FIG. 2, the recording signal source S has an impedance of RS
The input side amplifier circuit AMP1. It is connected to the rotary transformer RT via t. The rotary transformer RT can be expressed as a T-type equivalent circuit consisting of a series impedance element RI and a parallel impedance element LT, and the output terminal thereof is composed of a common base amplifier circuit BEI (BF2) and a negative feedback circuit NFL (NF2). Input circuit INI (IN
2) is connected.

When the input impedance of the input circuit INI (IN2) is R4, the lower cutoff frequency fL when looking from the recording signal source S to the rotary transformer RT side can be expressed as the following equation, and The high-frequency side cutoff frequency fH can be expressed as in the following equation.

Therefore, in equation (1), input circuit IN1 (IN2)
If the value of the input impedance R1fi of is selected to be a value sufficiently small with respect to the impedance R3 of the input side amplifier circuit A M P I N, the low-frequency cutoff frequency fL can be reduced based on equation (1). Can be done.

For example, when the value of the parallel impedance element LT is about t,y 10 (μH) as the rotary transformer RT, if the input impedance R4a of the input circuit INI (IN2) can be made about 1 [Ω]. , the cutoff frequency fL in the low range is f
It is thought that it can be reduced to about L = 15 (kHz).

On the other hand, the base-grounded amplifier circuit BEl in FIG.
(BF2) The independent input impedance ri is generally about 6 to 10 [Ω], whereas the common base amplifier circuit BEI (BF2) has a negative feedback circuit NFI (
By connecting NF2), the input circuit INI
The value of the input impedance R of (IN2) can be further lowered than the input impedance rt.

In other words, the equivalent circuit of the input circuit INI (IN2) in FIG. 1 is a common base amplifier circuit BE, as shown in FIG.
A negative feedback circuit NFI (N
F2) can be considered as a configuration in which F2) is connected. In this equivalent circuit, if the voltage appearing at the input terminal P1 when a current 1 ia is poured from the input terminal P1 is vl, then the input impedance R0 of the input circuit INI (IN2) seen from the input terminal P1 is given by the following equation. . Here, when the gain of the amplifier circuit BEI (BH3) is A, the voltage v0□ appearing at the output terminal P2
■. □=-AV! , 1. -1(4). Here, at the connection point P3 on the input end side of the feedback circuit NFI (NF2), if we calculate the current Iia flowing by setting the current sum to O based on Kirchhoff's law, we get ri R.

・・・・・・(5) It becomes. Therefore, by substituting equation (5) into equation (3), the input impedance R1I% becomes as follows.

Based on equation (6), if the amount of negative feedback is appropriately selected as necessary, the input impedance ri of the common base amplifier BEI (BH3) alone is about 6 to 10 (Ω). The value of the input impedance R1,% of the input circuit INI (IN2) can be set to 1 [Ω] or less.

Incidentally, when using a -a amplifier circuit, the input impedance ri of the amplifier circuit itself is about rt=10 (kΩ), and the amplification degree A is about A=50, so the value of the feedback resistor R7 is If R2 is selected to be about 300 [Ω], the input impedance R4a can be made to be about Rt-#6 (Ω), thus making the input impedance 10 [kΩ].
It is possible to significantly reduce the resistance from a value of about 6 [Ω] to about 6 [Ω].

In this manner, according to the configuration shown in FIG. 1, from the secondary winding N2 side of the rotary transformer RT to the input circuit INl (IN
By being able to reduce the input impedance RinO value in terms of 2), it is possible to further expand the cutoff frequency in the low range when looking at the rotary transformer RT from the recording signal source S. Practically speaking, for the embodiment of FIG.
The B bandwidth is 50 (kHz) to 150 (M
Hz) recording amplification circuit was realized.

Further, according to the configuration shown in FIG. 1, the negative feedback transistor Q4
(Q6) is connected to the differential amplification transistor Ql.
(Q2) to form a current mirror circuit MYI (MY2), good linearity can be maintained.

That is, from the secondary winding N2 of the rotary transformer RT to the emitter of the transistor Q3 (Q5) and the transistor Q
4 If the current flowing into the connection point of the collector of (Q6) is 1, then this current I is connected to the resistors R6 and R5 (R9 and R8
) by selecting the relationship R6<R5 (R9 (R8)), most of the current can be passed through the resistor R6 (R9). In this way, the differential amplification transistor Ql
The change in emitter voltage of (Q2) ΔV is Δ■Ar KRFΔ■ (R, = R6, R9) ...... (7
), the change ΔI in the current I flowing from the secondary winding N2 of the rotary transformer RT and the load resistance R
6 (R9), and this change can be obtained as a value proportional to MYI (MY2) in the current mirror circuit.
It can be generated at the emitter of the differential amplification transistor Ql (Q2) via the differential amplification transistor Ql (Q2). In this way, a recording current having good linearity with respect to the recording signal manually applied to the rotary transformer RT can be passed through the recording head HR.

Therefore, according to the configuration shown in FIG. 1, the adjustment of the recording circuit RK is
This can be easily realized by inputting recording signals of various signal levels as necessary via the rotary transformer RT, recording them on a recording medium, and monitoring the reproduction.

In addition, according to the configuration shown in FIG. 1, since the recording current is supplied from the differential amplifier circuit AMP that operates linearly to the recording head HR, it is possible to easily increase the recording current to a practically sufficient level. can flow.

Note that in the configuration of FIG. 1, the input circuits INI and IN
Since the current mirror circuits MYI and MY2 are provided in 2, the cutoff frequency f in the high range of the recording circuit RK,
However, in order to compensate for this, the first
Compensating transistors Qll and Q12 with a common base configuration may be inserted at both ends of the recording head HR, as shown in FIG. 4 with the same reference numerals assigned to corresponding parts. .

Further, as a method of improving the high frequency characteristics, the differential amplifier circuits AMP may be configured to be connected in cascade.

Furthermore, in the configuration shown in Fig. 1, the negative feedback transistor Q
If the current amplification factor hFE in the differential amplification transistors Q1 and Q2 is insufficient, a Darlington circuit configuration may be used instead.

Further, in the case of the embodiment shown in FIG. 1, bias resistors R4 and R7 are used as means for supplying bias voltage to transistors Q3 and Q5 of the common base amplifier circuits BEI and BF2.
Although the case has been described in which a transistor is used, instead of this, a bias may be applied using a transistor.

Furthermore, in the embodiment shown in FIG.
I inserted a DC cut capacitor C between the emitters of the differential amplification transistors Q1 and Q2 to prevent unnecessary current from flowing when there is no signal and the DC balance is not maintained. In this case, this capacitor C may be omitted.

In the embodiment shown in FIG. 1, the present invention is applied to a DVTR recording circuit, but the present invention can also be applied to an AVTR recording circuit that records analog signals instead.

According to the present invention, by reducing the input impedance seen from the secondary winding side of the rotary transformer, it is possible to expand the cutoff frequency [L] in the low range, and also to increase the linear By generating a recording current for the recording head by differential amplification, a recording circuit that can be adjusted more easily can be obtained.

[Brief explanation of drawings]

FIG. 1 is a connection diagram showing an embodiment of the recording circuit according to the present invention, FIG. 2 is a connection diagram showing an equivalent circuit around the rotary transformer, and FIG. 3 is the input circuit INI and IN2 of FIG.
FIG. 4 is a partial connection diagram showing the main part of another embodiment of the present invention. RK... Recording circuit, HR... Recording head, RT... Rotary transformer, AMP...
... Differential amplifier circuit, INI, IN2 ... Input circuit, BEI, BF2 ... Base-grounded amplifier circuit, NFl, NF2 ... Negative feedback circuit, LIN
...Linear operation circuit, MYl, MY2...
・Current mirror circuit.

Claims (1)

[Scope of Claims] (a) It has a pair of differential amplification transistors and a linear operation circuit that linearly differentially operates the pair of differential amplitude transistors, and (b) a differential amplifier circuit that supplies a recording current to the recording head; (b) a common-base amplifier circuit that receives a recording signal from a rotary transformer; A negative feedback circuit having a negative feedback transistor that provides negative feedback to the input terminal of the amplifier circuit, and a current mirror circuit that grounds the base of the negative feedback transistor to the base of one of the pair of differential amplification transistors. , comprising a pair of input circuits that generate the recording current in the differential amplifier circuit by respectively inputting recording signals input from the rotary transformer to the bases of the pair of differential amplifier transistors. recording circuit.