JPH06174403A - Cable length detecting circuit - Google Patents

Abstract

PURPOSE:To provide accurate cable length detection data regardless of the phase adjustment of the image signal by comparing, in phase, the signals immediately before and immediately after a phase controller, and extracting and excluding the phase adjustment quantity of the phase controller. CONSTITUTION:The pulse width of the synchronized separation output signal 29 transmitted from a camera head via a cable and synchronously separated is changed by a phase controller IC1 for the phase adjustment with various pulses of a camera control unit. This output signal 45 is compared with the input reference signal 30 from the outside by a phase comparator IC2, and the output is converted into DC voltage 47 by transistors Q1, Q2 and the integrating circuit of an amplifier IC3. The input 29 and the output 45 of the IC1 are compared in phase by a phase comparator IC5, the input/output phase difference by the IC1 is extracted, and the DC voltage 48 of the phase adjustment change in the IC1 is extracted by an IC7. The output 48 is subtracted from the output 47, and the cable length detection output 49 is obtained regardless of the phase adjustment by the IC1.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention detects an accurate cable length against deterioration of frequency characteristics of a transmission signal transmitted in a cable for connecting video equipment or equipment such as information processing equipment, and detects its frequency. The present invention relates to a cable length detection circuit for the purpose of compensating for characteristics.

[0002]

2. Description of the Related Art As a conventional technique, in the case of a video equipment, for example, in the connection between the television camera 25 and a camera control unit (hereinafter referred to as CCU) 27 shown in FIG. 2, the connection between the television camera 25 and the CCU 27. The longer the cable 26 is, the more deteriorated the frequency characteristic of the video signal is. Therefore, there is a method in which the television camera 25 or the CCU 27 compensates the deteriorated frequency characteristic of the video signal.
To perform this cable compensation, the cable length detection circuit that automatically detects the cable length and the manual type that switches the compensation characteristics according to the length of the cable to be used in advance is automatically provided. There is something to compensate. A block diagram of this conventional automatic cable length detection circuit is shown in FIG. FIG. 3 is roughly divided into a camera head 1 and a CCU 2. Here, the synchronous system of the camera head 1 includes a phase comparator 55, a voltage controlled oscillator (VCO) 56, and a counter 57.
Phase-locked loop consisting of
(Referred to as LL). The synchronous system of the CCU 2 is a phase lock loop (hereinafter referred to as a second PLL) including a phase comparator 4, a VCO 5 and a counter 7.
, Phase comparator 58, VCO 59, counters 60, 61
And a phase lock loop (hereinafter referred to as a third PLL). Of these, the first PLL circuit and the second PLL circuit are connected in series.

For example, in FIG. 3, when phase adjustment is performed by the phase adjuster 3, the output signal 64 of the phase adjuster 3 is compared with the signal 62 from the third PLL by the phase comparator 4 and synchronized with this. As a result, the output of the VCO 5 is advanced or delayed by the time delay of the signal due to the cable and the phase change adjusted by the phase adjuster 3. Therefore, the output 14 of the counter 63 is sent to the camera head 1 with a delay and a phase difference, and is synchronized with the camera head output signal by the first PLL. Here, the inside of the camera head 1 is PLL
The reason for the configuration is that the camera head alone can operate. The input signal of the phase comparator 8 which constitutes the cable length detection circuit is used for the horizontal synchronizing signal (for example, the phase comparators 4, 55 and 58) used in another PLL in order to improve the detection accuracy of the cable length. Signal (repeated pulse signal) that is n times the frequency of the current signal).
The counter output 61 used for the third PLL and the second PL
By comparing the phase of the counter output 7 used for L, highly accurate cable information can be obtained.

[0004]

In the above-mentioned prior art,
In FIG. 3, the output 18 of the phase comparator 4 when detecting the cable length is added with the phase adjustment amount adjusted by the phase adjuster 3 in addition to the transmission delay amount due to the cable length. Causes the cable length detection information to change. It is an object of the present invention to eliminate these drawbacks and detect the amount of change in the phase adjustment to obtain accurate cable length detection data regardless of the phase adjustment.

[0005]

FIG. 1 is a block diagram showing an overall configuration diagram of the present invention. In the figure, the difference from the prior art is that the phase comparator 10, the integrator 11, and the subtractor 1
2 is added. The signal 15 immediately before the phase adjuster 3 and the signal 17 immediately after the phase adjuster 3 are compared in phase by the phase comparator 10, and the phase adjustment component in the phase adjuster 3 is extracted. The output of the phase comparator 10 is added to the integrator 11, and the integrator 1
By subtracting the output signal 22 of 1 from the output signal 23 of the phase comparator 8, the phase adjustment amount of the phase adjuster 3 is eliminated. As a result, the output signal 24 becomes a cable length detection signal that is not affected by the phase adjustment of the video signal.

[0006]

As a result, in the cable length detection, a stable output voltage or detection information can be obtained regardless of the phase of the phase adjuster which adjusts the phase difference between the video signal from the camera head and the CCU.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT An embodiment of the present invention will be described below with reference to FIG. The sync separation output signal 29, which is transmitted from the camera head via the cable and separated in synchronization, is C
In order to adjust the phase relationship between various pulses of the CU, the pulse width is changed by the phase adjuster IC1 (one-shot IC). Since the output pulse 45 is an edged trigger, its phase is variable. The phase of the signal 45 and the input reference signal (for example, external synchronization signal) 30 from the outside are compared by the phase comparator IC2. The output of the phase comparator IC2 is converted into the DC voltage 47 by the integrating circuits of the transistors Q1 and Q2 and the amplifier IC3. On the other hand, the sync separation output signal 29 and the output 45 of the phase adjuster IC1 are compared in phase by the phase comparator IC5, and the input / output phase difference by the phase adjuster IC1 is extracted. The output pulse of this phase comparator IC5 is applied to transistors Q3 and Q4, amplifiers IC6 and IC.
The integrator circuit 7 and the amplifier 7 extract the DC voltage 48 corresponding to the phase adjustment change in the phase adjuster IC1. Then, by subtracting the output 48 corresponding to the phase adjustment change from the output 47 and setting it to an appropriate voltage by the amplifier IC4, a cable length detection output 49 which is not affected by the phase adjustment of the phase adjuster IC1 can be obtained. .

Next, another embodiment is shown in FIG. The difference from FIG. 1 is that the output 51 of the phase comparator 32 is subtracted from the output of the phase comparator 8 through the gate circuit 31, this output 54 is integrated by the integrator 33, and the cable length detection output 34
Is to get. Also, this cable length detection output 34
, Is used as an analog output by the integrator 33, but the same operation can be performed by adding this as a digital signal to the computer as a cable length detection output. In FIG. 6, a DC voltage obtained by integrating the output of the phase comparator 38 by the integrator 37 is added to the power supply voltage section of the waveform forming circuit 35 to change the pulse phase of the waveform forming circuit output, thereby eliminating the influence of the phase adjustment. The extracted cable length detection output 40 is extracted. Figure 7
The specific circuit is shown in. The input and output of the phase adjuster (one-shot IC) IC1 are phase-compared by a phase comparator IC5, and the phase difference pulses are Q3, Q4, IC6, IC7.
Is integrated into a current-voltage output 50. This output 50
Is connected to an element that determines the time constant connected to the waveform forming circuit IC8, thereby correcting the phase change of the phase adjusting circuit portion in the cable length detecting circuit and eliminating the influence of the phase adjustment.

[0009]

According to the present invention, the video signal of the camera and the C
Even when the phase adjustment with the CU is performed, a stable cable length detection output can be obtained regardless of the phase adjustment.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention.

FIG. 2 is a diagram showing a connection state of a camera and a CCU cable.

FIG. 3 is a block diagram of a conventional camera and a CCU.

FIG. 4 is a circuit diagram showing an embodiment of the present invention.

FIG. 5 is a block diagram showing another embodiment of the present invention.

FIG. 6 is a block diagram showing another embodiment of the present invention.

FIG. 7 is a specific circuit diagram of FIG.

[Explanation of symbols]

1 Camera Head 2 CCU 3 Phase Adjuster 4, 8, 10, 32, 36, 38, 55, 58 Phase Comparator 5, 56 VCO 7, 57 Counter 9, 11, 33, 37, 39 Integrator 12 Subtractor 13 , 14, 15 Cable 16 External reference signal

Claims (1)

[Claims] 1. A cable is connected between two electronic devices,
When transmitting and receiving a signal between these devices, the phases of the signal sent from the first device to the second device and the signal received by the second device and sent back to the first device are compared, and both are compared. In a cable length detection circuit that includes a phase comparison circuit for synchronously coupling signals, and detects the cable length by a change in the output of the phase comparison circuit, the phase of the signal sent from the first or second device is intentionally changed. A cable length detection circuit comprising: a circuit for changing and a means for controlling the cable length detection data according to the phase amount changed by the circuit.