JPH02137521A - A/d converter for magnetic recording and reproducing device - Google Patents

Abstract

PURPOSE:To attain A/D conversion with less adjustment portions by providing a resistance circuit network to an output terminal of a switching circuit, applying a prescribed voltage to the comparator by the resistance circuit as a reference voltage of the comparator and obtaining a digital output from the output terminal of a controller. CONSTITUTION:An analog signal is fed to a sample-and-hold circuit 27 as an input and a comparator 28 whose one input terminal is connected to the output of the circuit 27 is provided. Then the controller 36 is provided, which integrates an analog signal and whose output terminal is connected to an input terminal of a reference voltage generator, and a switching circuit 33 is provided, whose input is connected to the output of an integration circuit 29 and to the output of the controller 36 and whose output is connected to other reference voltage input terminal of the comparator 28. A resistance circuit network 36 is provided to the output terminal of the circuit 33, a prescribed voltage is fed to the comparator 28 by the circuit network 34 as the reference voltage of the comparator 28 and a digital output is obtained from output terminals 42, 43...45 of the controller 36.

Description

DETAILED DESCRIPTION OF THE INVENTION (A) Field of Industrial Application The present invention relates to an AD converter that is most suitable for simple video recording and reproducing among magnetic recording and reproducing devices.

(b) Conventional technology In general, for home color VTRs, three systems have been put into practical use: the β system using the β format as a cassette type, the VH8 system using the VHS format, and the 8mm system, which has a standardized standard. A dedicated cassette is also used, and VTRs of the same format are compatible and can be used for recording and playback.

For example, signal processing during recording and playback is based on analog signal processing, as described in 'NHK Home Video Technology' edited by Japan Broadcasting Corporation, published by Japan Broadcasting Publishing Association, P67 and P93.
~96.

(c) Problems to be Solved by the Invention In the conventional example described above, each component of the luminance signal and the color signal is amplified by a linear amplifier, and most of the processing of the color signal, etc., is performed using analog processing. However, there are many adjustment points, and the number of steps involved in assembling the device is large, which increases the cost of the device.

In view of the above-mentioned drawbacks, an AD converter for use in the magnetic recording/reproducing apparatus of the present invention is proposed for use in a simple type, that is, a tape cassette called a C cassette for audio, which is capable of recording and reproducing data.

(d) Means for Solving the Problems The present invention provides an AD converter for a magnetic recording/reproducing device that converts an analog signal from an image sensor into a digital signal, which includes a sample/hold circuit to which the analog signal is applied as an input, and a sample/hold circuit to which the analog signal is input. - a comparator with one input end connected to the output side of the hold circuit, an integrating circuit that integrates the analog signal and whose output end is connected to the input end of the reference voltage generation means, and an output end of the comparator. and a switching circuit whose input side is connected to the output side of the reference voltage generating means and the output side of the controller, and whose output side is connected to the other reference voltage input terminal of the comparator, A resistor network is provided at the output end of the switching circuit, a predetermined voltage is applied to the comparator by the resistor network as a reference voltage of the comparator, and a digital output is obtained from the output end of the controller.

(e) Effect In the present invention, when converting an analog video signal into a digital signal, the analog video signal applied to the sample/hold circuit is compared with a reference voltage, and a value weighted by the reference voltage by a resistor network is calculated. Since the reference voltage obtained by DA conversion at the output of the controller can be varied depending on the magnitude of the average value of the analog input, the digital output operates as if automatic gain control is operating.

Embodiment) The drawings show an AD Lombard of the magnetic recording and reproducing device of the present invention, FIG. 1 is a block diagram of the main part, FIG. 2 is an overall block diagram of the device, and FIG. 3 is an explanatory characteristic diagram of the AD converter. Fourth
The figure shows a timing chart of the AD converter.

In the drawings, (1) is an image sensor as a photoelectric conversion element, (2) is a first preamplifier, (3) is a DC regeneration circuit, (4) is a variable step AD converter, (5) is a pre-emphasis circuit, and (6) is a DC regeneration circuit. ) is a counter type FM modulator,
(7) is a head driver, (8) is a magnetic head, (9)
is the first switching circuit, (10) is the second Benoanbu,
(11) is a limiter amplifier, 12) is a counter type FM
Demodulator, <13) is a controller that outputs various control signals, (14) is a sensor driver, (15) is an iris adjustment circuit, 16) is an image integration circuit, (17) is an iris adjustment terminal, (18) is a control input terminal, (19) is a de-emphasis circuit, (20) is a dropout detection circuit, (21) is a second switching circuit, (22) is an image memory, (23) is a DA converter, and (24) is a mixing circuit. vessel,
(25) is an RF modulator, (26) is a magnetic tape, the image signal is obtained from the image sensor (1) as an analog video signal, and the image sensor output is amplified by the first preamplifier (2) and included therein. Only valid signal components are extracted.

The next stage DC regeneration circuit (3) outputs OP B (0ptical Black) of the image sensor (1).
DC reproduction is performed using the signal as a reference, and the DC reproduced video signal is applied to a video integration circuit (16) and a variable step AD converter (4). In the former, the average value, peak value,
Alternatively, a value corresponding to the intermediate value can be obtained by setting a desired time constant.

As a result, the video integrated output signal is sent to the iris adjustment circuit (15).
The sensor driver (14) is connected to the sensor driver (14) through the iris, and iris adjustment is performed by reverse charge transfer or the like. In this case, when using a mechanical iris adjustment method, the output of the iris adjustment circuit drives the driver of the mechanism.

On the other hand, the latter is applied to a variable step AD converter (4). This changes the step according to the input and
This is a circuit that performs conversion. This function is automatic gain control (AGC) of the oven loop, and even if the average value of the input signal fluctuates, conversion data with a substantially constant average value can be obtained. One of the outputs of the variable step AD converter (4) is sent to the second switching circuit (21) as a direct display signal.
) to the image memory (22) and the memo 1 bar 2
2), the composite video signal is outputted through the DA converter (23) and mixer (24).

On the other hand, data corresponding to high frequency parts of the image is emphasized through a pre-emphasis circuit (5), and applied to a counter-type FM modulator (6), where the digital signal is FM-modulated and sent to the head driver (7) and the first switching circuit. (9
) to the magnetic head (8), and the magnetic tape (2
6) can be recorded.

Next, during reproduction, the video signal recorded on the magnetic tape (26) is detected as an FM signal by the magnetic head (8), and the video signal is detected as an FM signal by the first switching circuit (9) - second preamplifier (10) -
Limiter amplifier (11) - Power counter type FM demodulator (12)
) - second switching circuit (21) - image memory (22
)-DA converter (23)-mixer (24), a composite video signal is obtained. The concrete configuration of the variable step AD converter (4) shown in FIG. 2 is shown in FIG. The voltage is applied to the negative end of the comparator (28) and passes through an integrating circuit (<31) consisting of a resistor (29) and a capacitor (30), and its center value constitutes a reference voltage generation source ζ distortion as a reference voltage generation means. It is applied to the amplifier 32〉 which has an amplification factor of n times. The output of the amplifier (32) is an AD conversion reference voltage (
Vr). At this time, the switching circuit (
33), a control signal is output from the controller (36) according to the output of the comparator (28). Here, the resistance value R of the weighting resistors (37) (38) (39) (40>)
, R2, ......R, (for example, each bit 1, 2, 4
．． 8), the resistance value R of the resistor (41), and the capacitance value (Cp) of the capacitor (35)
Even if the digital output from (44) and (45) is constant, the value DA (digital-to-analog converted) from the controller (36) varies depending on the average value of the analog input applied to the terminal (46). (Even when the digital output is constant) The switching circuit (33) is connected to latches (47) (48) (49) (50) and analog switches (51) (52) (53) corresponding to each bit. (54) has a power supply path for each of the resistors (37), (38), (39), and (40), and according to constant current operation, the resistance value of each resistor R□
,R. ,R. The comparison terminal reference voltage is applied to the comparator (28) at the resistance ratio of R4 and Ro.The voltage at point P is the highest value of the digital data, that is, the switching circuit (33
), αX
The resistance value is set to be Vr/n. M in the diagram
SB indicates the most significant digit, and LSB indicates the least significant digit.

In the example shown in Figure 4, the ratio α between the dynamic range and the initial value is set to 2.5, which can be set to any desired value.

As shown in this case, the dynamic range is set with a margin for the MSB value.

Here, as shown in Fig. 3, the clock signal (Fig. 4 (a)
), the reset signal (R) is shown in FIG. The signals shown in (c) to (h) are output.

The output signal has a waveform that rises and falls every time the clock signal (CLK) rises.

With the above configuration, the dynamic range of AD conversion changes in response to the average value of the analog input, and accordingly, the step in digital conversion, that is, the voltage step can be changed depending on the magnitude of the analog input, The sharpness of the screen can be made to be the same for small (dark screen) and large (bright screen) analog inputs, just like the automatic gain control (AGC) circuit in the analog signal processing circuit. Become.

In FIG. 1, when reflecting the peak value of the analog input signal to the reference voltage (Vr), a resistor (29
) by connecting a series circuit consisting of a diode (55) and a resistor (56) in parallel, a configuration that follows the peak value from average value operation can be obtained.

(G) Effects of the invention According to the AD converter of the magnetic recording/reproducing device of the present invention,
When processing an analog signal obtained from an image sensor, digital processing can be performed compared to automatic gain control (AGC) using a linear circuit, so it is possible to obtain a gain that requires fewer adjustments in the subsequent signal processing, and also When using digital signal processing called histogram processing, the image signal has a wide range of brightness and darkness, and if you want to process it with a wide dynamic range,
0 bit is required, but in the present invention, for example, steps can be changed for signals on both bright and dark screens using several bits, and the merits of both analog processing and digital processing can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram of the AD converter of the magnetic recording/reproducing device of the present invention, FIG. 2 is a block diagram of the device, FIG. 3 is an explanatory characteristic diagram of the converter, and FIG. 4 is a timing chart of the converter. . 1)...Image sensor, (4)...Variable steering wheel
(6)...Counter type FM modulator, (8)...Magnetic head, (26)...Magnetic tape, (27)...Sample/hold circuit,
(28)...Comparator, (29>...Integrator circuit, (
32)...Amplifier, (33>...Switching circuit, (34)...Resistance circuit network.

Claims (1)

[Claims] (1) In an AD converter of a magnetic recording/reproducing device that converts an analog signal including an image output obtained from an image sensor for photoelectric conversion into a digital signal, a sample/hold circuit to which the analog signal is added as an input; a comparator with one input end connected to the output side of the sample-and-hold circuit; an integrating circuit that integrates the analog signal and whose output end is connected to the input end of the reference voltage generating means; and an output of the comparator. and a switching circuit whose input side is connected to the output side of the integrating circuit and the output side of the controller, and whose output side is connected to the other reference voltage input terminal of the comparator, A magnetic device characterized in that a resistor network is provided at the output end of the switching circuit, a predetermined voltage is applied to the comparator by the resistor network as a reference voltage of the comparator, and a digital output is obtained from the output end of the controller. AD converter for recording/playback equipment.