JPH05107626A - Camera and magnetically recorded information reproducing circuit - Google Patents

Abstract

PURPOSE:To decrease noise voltages by providing the magnetically recorded information reproducing circuit constituted by connecting a magnetic head to an amplifier circuit of a high-input impedance and connecting the output terminal of this amplifier circuit to a low-pass filter of 4th order or above. CONSTITUTION:The camera for which a film with a magnetic recording part is used is provided with the magnetically recorded information reproducing circuit 19 constituted by connecting the magnetic head 1 for reproducing the magnetically recorded information of the film to the amplifier circuit of the high-input impedance and connecting the output terminal of this amplifier circuit to the low-pass filter of the 4th order or above. The magnetically recorded information reproducing circuit 19 is lower in the cut-off frequency of the low-pass filter than the resonance frequency of the magnetic head 1 at the time of packaging in such a case. The electrostatic capacity on the periphery of the magnetic head 1 is decreased by providing the filter of the higher order behind the output of the amplifier of the initial stagein such a manner, by which the noise voltages superposed on the output of the amplifier of the initial stage are decreased. The signals are thus reproduced without errors even if the output signal from the magnetic head 1 is small.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a camera using a film with a magnetic recording section, and a magnetic recording information reproducing circuit for reproducing information recorded in a magnetic recording section mounted on the camera.

[0002]

2. Description of the Related Art Conventionally, a reproducing circuit for reproducing information recorded in a magnetic recording portion of a film has a circuit as shown in FIG. 13 which has been proposed by the same applicant as the present application.
Here, 1 is a magnetic head, 2, 3, 4, and 5 are bias resistors, 6 is a differential amplifier circuit (for example, AD524 manufactured by Analog Devices, Inc.), 7 and 8 are resistors, and 9 is an operational amplifier (OP.
Amplifiers, for example, Texas Instruments-TI TL071, 13 and 15 are comparators (for example, T
I company LM2903), 14 and 16 are reference voltage sources, 17
Is an RS flip-flop (for example, SN742 manufactured by TI)
79) and 18 are capacitors (capacity is Co [F]). Here, the voltage generated at both ends of the magnetic head 1 is amplified by the differential amplifier and then further amplified by the OP amplifier 9 with the amplification degree according to the ratio of the resistors 7 and 8. The output of the OP amplifier 9 is an analog output.

Next, the analog outputs are comparators 1 and 1.
Input to 5. In the comparator 13, the _negative input terminal is connected to the reference voltage 14 having the voltage value V _COMPH . or,
The + input terminal of the comparator 15 is connected to the reference voltage 16 having the voltage value V _COMPL . Therefore, the analog output is V
_{When COMPH} is exceeded, the output of the comparator 13 becomes 1 (H level), and when the analog output falls below V _COMPL , the output of the comparator 15 becomes zero (L level). The digital output as the output of the RS flip-flop 17 has a waveform as shown in FIG. 14 according to the analog output.
However, the horizontal axis is time, and the digital output uses the time between falling edges as one clock of one signal, and pulse position modulation (Pulse Position Positioning) that determines 0 or 1 of the signal according to the time from the falling edge to the rising edge. Modul
ation) system. Where the fall-
0 when the time between rising edges is shorter than 1/2 clock time,
It is 1 when it is long. By connecting the capacitor 18 to the magnetic head 1 in parallel, the peak of the real part of the impedance of the magnetic head 1 could be lowered as shown in FIG. In FIG. 15, the horizontal axis represents frequency and the vertical axis represents the real part of impedance. As shown in the figure, the magnetic head exhibits a resonance state in the real part of impedance as shown in the figure.

Therefore, referring to FIG.
The noise voltage that increases according to the real number part of the impedance due to the addition of is decreased at 0 to 100 KHz. Therefore, the noise voltage at 0 to 100 KHz was lowered by adding the capacitor 18. Since the frequency band required for signal reproduction is about 100 Hz to 40 KHz, the noise can be reduced by adding the capacitor 18 when considering a reproduction system using a filter with a small order.
The horizontal axis of FIG. 16 is the frequency, and the vertical axis is the logarithmic display of the analog output voltage when there is no input signal to the magnetic head 1.

[0005]

However, in the conventional example described above, when the output signal from the magnetic head 1 is small in a camera having a slow film feeding speed,
The output signal becomes smaller than the noise voltage level, and there is a problem in S / N when the signal is reproduced. The present invention has been made to solve the above problems, and it is an object of the present invention to provide a camera capable of reproducing a signal without error even when an output signal from a magnetic head is small in a camera having a slow film feeding speed. To aim.

[0006]

In order to achieve the above object, the camera of the present invention connects a magnetic head for reproducing magnetically recorded information on a film to an amplifier circuit of high input impedance, The magnetic recording information reproducing circuit has an output terminal connected to a low-pass filter of fourth order or higher, and this magnetic recording information reproducing circuit has a low-pass filter which is lower than the resonance frequency of the magnetic head at the time of mounting. The cutoff frequency is low, and the magnetic recording information reproducing circuit according to claim 3 is arranged near the magnetic head so that the resonance frequency of the magnetic head is higher than the reproducing frequency of the magnetic recording information. According to another aspect of the present invention, in the magnetic recording information reproducing circuit, the magnetic head is surrounded by electrodes which are held at the same voltage as the terminal voltage of the magnetic head. It is.

[0007]

According to the present invention, a noise filter superimposed on the analog output can be reduced by providing a high-order filter after outputting the analog output to reduce the electrostatic capacity around the magnetic head.

[0008]

1 to 9 show an embodiment of the present invention.
FIG. 1 is a block diagram of an electric circuit unit according to an embodiment of the present invention, FIG. 2 is a perspective view showing a configuration of a camera of the present invention, and FIGS. 3 to 5 are views showing flow charts of an embodiment of the present invention. 6 is a diagram showing a magnetic reproducing circuit of an embodiment of the present invention, FIG. 7 is a diagram showing a real part of impedance of a magnetic head of an embodiment of the present invention, and FIG. 8 is a noise voltage characteristic of the embodiment of the present invention. FIG. 9 is a diagram showing a voltage waveform of one embodiment of the present invention. 1 to 9, 1 is a magnetic head, 2, 3,
4, 5 are resistors for bias, 6 is a differential amplifier circuit (for example, AD524 manufactured by Analog Devices, Inc.), 7, 8 are resistors, 9
Is an OP amplifier (for example, TL071 manufactured by TI), 10 is a filter circuit block, 11 and 12 are filter circuits (for example, SR-4BL3 manufactured by NF circuit block), 13 and 15
Is a comparator circuit (for example, LM2903 manufactured by TI),
Reference numerals 14 and 16 are reference voltage sources, 17 is an RS flip-flop (for example, SN74279 manufactured by TI), 19 is a magnetic recording / reproducing circuit including FIG. 6, 20 is a microcomputer,
Reference numeral 21 is a release switch, 22 is an auto focus (AF), auto iris (AE) in the camera, a shutter control circuit, 23 is a motor driver, 24 is a feeding motor, 25 is a main switch, 26 is a perforation detection switch, and 27 is a magnetic switch. Film with recording unit, 28 is a magnetic recording unit, 29 and 30 are perforations, 31 is a film feeding fork, 32 is a film feeding gear unit, 33 is a magnetic head pressing pad, 34 is a cartridge, and 35 is a release button. is there.

In FIG. 1, the microcomputer 20 detects the main switch 25 to start the operation, detects the release switch 21, and detects the AF, AE, and shutter control circuit 2.
2, the release operation is performed, and the feeding motor 24 is driven to feed the film 27. Also,
The signal from the magnetic head 1 is converted into a digital signal by the magnetic recording / reproducing circuit 19, and the signal is decoded in the microcomputer 20.

In FIG. 2, the release switch 21 is turned on by operating the release button 35. The magnetic head 1 is covered with the film 27 by a member (not shown) and the pressing pad 33.
It is pressed against the upper magnetic recording portion 28. Film 27
Is fed by the feeding motor 24 via the feeding fork 31 and the feeding gear unit 32.

The operation of the embodiment shown in FIGS. 1 and 2 will be described with reference to the flow charts shown in FIGS. FIG. 3 is a flowchart of the main program. First, start (S
101). Next, it is checked whether the main switch 25 is ON (S102). It is checked whether the film 27 has been prewound (S103). In the camera of this embodiment, the film 27 is drawn out from the cartridge 34 in advance before shooting.
It is a prewind camera that returns the film 27 to the cartridge 34 for each frame. Therefore, whether or not the film 27 has been prewound is recorded in the memory in the microcomputer 20, and it is checked whether the film 27 has been prewound based on the value of the memory. Then, the prewind subroutine is entered, which is shown in detail in FIG.
Will be explained. Then enter the release sequence (S
105). This release sequence will also be described in detail with reference to FIG. Finally, it is checked whether the main switch 25 is ON (S106). If it is ON, the release sequence (S105) is performed. If it is OFF, the operation ends (S107).

The processing of the prewind subroutine of FIG. 4 will be described. First, the operation is started (S20
1), the feeding motor 24 is turned on, and the feeding gear unit 3
The film 27 is taken out from the cartridge 34 through the 2 and the feeding fork 31 (S202). Then, it is checked whether the perforation detection switch 26 is ON or OFF (S203). The perforation detection switch 26 is a perforation 29.3 on the film 27.
It turns ON at the 0 position. Next, the perforation counter is reset. That is, the counter for counting the number of perforations in the microcomputer 20 is reset to zero (S204). Then, the timer counter is started (S205). Although the movement of the film 27 is detected by the perforation detection switch 26, when the perforation detection switch 26 does not turn on and off during a certain time (here, T ₀ ), it is determined that the film 27 has stopped. Next, the magnetic recording / reproducing circuit 19 is turned on (S206), the digital output signal of the magnetic recording / reproducing circuit 19 is decoded, and the film 2
The information recorded in the magnetic recording unit 28 on the No. 7 is reproduced (S
207). It is checked whether the timer counter has exceeded T ₀ (S208). When the timer counter is smaller than T ₀ , the perforation detection switch 26 is checked (S212). When T ₀ or more, the film 27 did not move for some reason.
FF is performed (S209), and the feeding motor 24 is stopped (S
210). Then, the process returns to the starting point (S211). next,
In S212, the perforation detection switch 26 is checked, and the perforation detection switch is turned off.
If so, the timer counter is checked again (S20
8). On the other hand, when it is ON, the perforation counter is incremented by 1 (S213). Since the number of perforations is known in advance from the maximum number of frames of the film, when the number of perforations increases due to any factor, the reproducing circuit 19 is turned off as described above (S209), and the feeding motor is moved. 24 is stopped (S21
0). Therefore, it is checked whether the perforation counter has exceeded a predetermined number (S214), and if not, the timer counter starts counting (S2).
15) It is checked whether the timer counter has exceeded a certain time T ₀ (S216). When the timer counter <T ₀ , the reproducing circuit 19 is turned off (S209), and the feeding motor 24
Is stopped (S210). Further, the perforation detection switch 26 is checked (S217).

The operation of the release sequence of FIG. 5 will be described. First, the operation is started (S301), and it is checked whether or not the release switch 21 is turned on (S301).
302), the same autofocus (A
F), auto iris (AE), shutter control AF,
This is performed by controlling the AE and shutter control circuit 22 (S303). Until the perforation detection switch 26 comes to the position of the perforations 29, 30, the feeding motor 24 is driven in the direction opposite to that in the prewind (S304).

The main part of the present invention will be described below with reference to FIG. Reference numeral 1 is a magnetic head, and reference numerals 2, 3, 4, and 5 are bias resistors of a differential amplifier circuit. This bias resistor 2, 3,
4 and 5 are 10 in comparison with the impedance of the magnetic head 1.
It is more than twice the value. The bias current of the differential amplifier circuit 6 can be supplied by the bias resistors 2, 3, 4, and 5. The OP amplifier 9 amplifies the output of the differential amplifier circuit 6 with an amplification degree determined by the resistors 7 and 8. The filter circuit block 10 is composed of filter circuits 11 and 12. Here, SR-4B manufactured by NF Circuit Blocks
L3 is used. One filter circuit can form a fourth-order low-pass filter. Therefore, in the filter circuit block 10, an 8th-order low-pass filter is configured by 2 stages of 4th-order filters. Although there are several methods for constructing the filter, the Butterworth type or the Bessel type is desired here in view of the waveform transfer characteristics. The output of the filter circuit block 10 is used as a filter output. The reference voltage V _COMPH 14 for comparison is connected to the-input terminal of the comparator 13. Therefore, when the filter output exceeds V _COMPH , the output of the comparator 13 becomes 1 (HI) output. A reference voltage V _COMPL 16 for comparison is connected to the + input terminal of the comparator 15. Therefore, when the filter output is smaller than V _COMPL , the output of the comparator 15 becomes 1 (HI) output. RS flip-flop circuit 17
When 1 is input to the S input terminal and 0 is input to the R input terminal, 1 is output to the output terminal Q. When zero is input to the S input terminal and 1 is input to the R input terminal, zero is output to the output terminal Q. The output Q of the RS flip-flop circuit 17 is used as a digital output.

Here, FIG. 7 is a diagram showing a real part characteristic of the frequency vs. impedance of the magnetic head 1. The peak value of the real part of the impedance is C _{0 in} the conventional example.
It becomes larger than the case where the capacitor 18 of [F] is added, and the frequency also moves to the higher side. When there is no input signal in the magnetic head 1 and the noise voltage generated from the magnetic head 1 is observed in the analog output, FIG.
As shown in. Further, FIG. 8 is a diagram showing the frequency-versus-noise voltage. The noise voltage V _{noise in} FIG. 8 is almost {4k
It is proportional to TBReal (Z)} ^1/2 . However, k: Boltzmann constant 1.38 × 10 ⁻²³ [J
/ ° K] T: Absolute temperature [° K] B: Frequency band [Hz] Here, every 1 Hz Real (Z): Real part of impedance Therefore, the peak of noise voltage is analog output (no C ₀ )
Is larger than the analog output (with C ₀ ), and the frequency is moving to the higher side. However, when the noise voltage at the filter output is observed, it becomes as shown by the dotted line in FIG. Here, a case where the cutoff frequency of the low-pass filter of the filter circuit block 10 is set to around 15 KHZ is shown. At this time, the filter output (without C ₀ ) is
Compared to the filter output (with C ₀ ), it is reduced over the entire frequency band. However, it is clear from FIG. 8 that the noise voltage of the filter output is reduced to about 1/2 to 1/3 as compared with the analog output. FIG. 9 is a diagram showing changes with time of analog output, filter output, and digital output of the amplifier circuit shown in FIG. In the analog output shown in FIG. 9, the noise voltage superimposed on the output of the magnetic head 1 is the reference voltages V _COMPH and V _{COMPL of the} comparators 13 and 15.
There was a case that the signal was exceeded and the wrong signal was reproduced. On the other hand, in the filter output, the noise voltage dropped to 1/2 to 1/3 as shown in FIG. 9, so that a digital output signal could be obtained without error. Further, since the capacitor 18 (FIG. 13) added to the magnetic head 1 was removed, the noise voltage could be further reduced.

FIG. 10 shows another embodiment of the present invention.
1 is a magnetic head, 36 and 37 are input patterns on the substrate 43 of the differential amplifier 38, 38 is a differential amplifier IC chip,
Reference numeral 40 is a power supply pattern on the substrate 43, 41 is a GND pattern on the substrate 43, 39 is a bypass capacitor, and 42 is an output pattern on the substrate 43. As is clear from FIG. 10, the distance between the magnetic head 1 and the IC chip of the differential amplifier 38 is shortened, that is, the IC chip is mounted on a chip-on-board, and the electrostatic capacity existing there is considered from the viewpoint of mounting. I reduced it. Therefore, since the electrostatic capacitance is further reduced, the noise voltage can be reduced even if the same high-order filter is used.

11 and 12 are views showing still another embodiment of the present invention. In FIGS. 11 and 12, 1 is a magnetic head, 36 and 37 are input patterns on the substrate 43 of the differential amplifier 45, 39 is a bypass capacitor, and 40 is substrate 4.
3 is a power supply pattern, 41 is a GND pattern on the substrate 43, 44 is a feedback pattern on the substrate 43, and 45.
Is a differential amplifier, 47, 48, 49 and 50 are input protection diodes, 51, 52, 53 and 54 are bias resistors,
55, 56, 57, 58 are OP amplifiers, 59, 60, 6
Reference numerals 1, 62, 63, 64 and 65 are resistors that determine the amplification degree. The pin numbers of the differential amplifier 45 are shown for the input terminal and the output terminal. The differential voltage applied to the differential input terminals 101, 102 is {1+ (R ₆₀ + R ₆₁ ) / R ₅₉ } (R ₆₃ / R ₆₂ ), where R ₆₂ = R ₆₄ , R ₆₃ = R ₆₅ It is amplified by the amplification degree. The OP amplifier 55 outputs the same voltage as the-input terminal voltage of the OP amplifier 57, that is, the + input terminal voltage of the OP amplifier 58. Therefore, the output of the OP amplifier 55 is fed from the third terminal of the differential amplifier 45 to the feedback pattern 44.
The voltage of the input pattern 37 and the voltage of the feedback pattern 44 become equal to each other, and the capacitance is canceled.

[0018]

As described above, in the camera of the present invention and the magnetic recording information reproducing circuit mounted therein, a high-order filter is provided after the output of the first-stage amplifier to reduce the capacitance around the magnetic head. The noise voltage superimposed on the output of the first-stage amplifier can be reduced, and the signal can be reproduced without error even when the output signal from the magnetic head is small in a camera having a slow film feeding speed.

[Brief description of drawings]

FIG. 1 is a block diagram of an electric circuit unit according to an embodiment of the present invention.

FIG. 2 is a perspective view showing a configuration of a camera of the present invention.

FIG. 3 is a flowchart showing an operation in one embodiment of the present invention.

FIG. 4 is a flowchart showing an operation in one embodiment of the present invention.

FIG. 5 is a flowchart showing an operation in one embodiment of the present invention.

FIG. 6 is a diagram showing a magnetic reproducing circuit according to an embodiment of the present invention.

FIG. 7 is a diagram showing a real part of impedance of a magnetic head according to an embodiment of the present invention.

FIG. 8 is a diagram showing a noise voltage characteristic of an example of the present invention.

FIG. 9 is a diagram showing voltage waveforms according to an embodiment of the present invention.

FIG. 10 is a plan view of a chip showing another embodiment of the present invention.

FIG. 11 is a plan view of a chip showing still another embodiment of the present invention.

FIG. 12 is a circuit diagram showing still another embodiment of the present invention.

FIG. 13 is a diagram showing a conventional amplifier circuit.

FIG. 14 is a diagram showing output waveforms of respective parts of FIG.

FIG. 15 is a diagram showing the impedance of the circuit of FIG.

16 is a diagram showing a noise voltage of the circuit of FIG.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 magnetic head 2,3,4,5 bias resistance 6 differential amplification circuit 7,8 resistance 9 OP amplifier 10 filter circuit block 11,12 filter circuit 13,15 comparator circuit 14,16 reference voltage source 17 RS flip-flop 19 magnetic recording / reproducing circuit 20 microcomputer 21 release switch 22 auto focus (AF), auto iris (AE), shutter control circuit in camera 23 motor driver 24 feeding motor 25 main switch 26 perforation detection switch 27 film with magnetic recording section 28 Magnetic Recording Section 29, 30 Perforation 31 Film Feed Fork 32 Film Feed Gear Unit 33 Magnetic Head Press Pad 34 Patrone 35 Release Button

Claims (4)

[Claims] 1. In a camera using a film with a magnetic recording portion, a magnetic head for reproducing magnetically recorded information on the film is connected to an amplifier circuit with high input impedance, and the output terminal of the amplifier circuit is of a fourth or higher order. A camera having a magnetic recording information reproducing circuit connected to a low-pass filter. 2. The magnetic recording information reproducing circuit according to claim 1, wherein the cutoff frequency of the low-pass filter is lower than the resonance frequency of the magnetic head when mounted. 3. The magnetic recording information reproducing circuit according to claim 1, wherein the magnetic recording information reproducing circuit is arranged near the magnetic head so that the resonance frequency of the magnetic head when mounted is higher than the reproducing frequency of the magnetic recording information. Magnetic recording information reproducing circuit. 4. The magnetic recording information reproducing circuit according to claim 1, wherein the magnetic head is surrounded by electrodes which are held at the same voltage as the terminal voltage of the magnetic head.