WO1998017062A1

WO1998017062A1 - Level control for a broadband distribution system

Info

Publication number: WO1998017062A1
Application number: PCT/US1997/019035
Authority: WO
Inventors: James R. Fetterolf, Sr.; Steven L. Flickinger; Ellwood D. Nonemacher; Joseph P. Preschutti
Original assignee: The Whitaker Corporation
Priority date: 1996-10-11
Filing date: 1997-10-10
Publication date: 1998-04-23
Also published as: AU5084698A

Abstract

This invention provides a level control system for achieving a consistent desired signal level at each of the outlets (27) of a broadband signal distribution system where the outlets (27) are each subject to signals experiencing varying amounts of attenuation. The level control system has two subsystems (10, 80). The cable system level control subsystem (10) consists of a closed loop feedback circuit having an RF pilot detector (60) for detecting a pilot signal generated at the distribution unit (38), a level control circuit (62), and a pair of cable simulating attenuators (16, 19) which are controlled by the level control circuit (62). The modulator level control subsystem (80) consists of a pair of flat response attenuators (86, 88) connected in series and a closed loop feedback circuit consisting of a broadband RF detector (96) and a level control circuit (98) connected to the output of the broadband RF detector for driving both flat response attenuators (86, 88) whereby a desired signal level output is achieved on the system output (21).

Description

LEVEL CONTROL FOR A BROADBAND DISTRIBUTION SYSTEM

This invention is related to a broadband signal distribution system, and more particularly to signal level control in such a system.

There are numerous instances where it is desired to distribute broadband signals modulated on to RF carriers over wire within a relatively local area, such as a building. A particular application is the distribution of video signals. For example, a school may have a number of classrooms and administrative offices, each having a television, and it may be desired at a given time to provide a program to all of the classrooms and offices, originating either from a source within one of the classrooms or offices, such as a VCR or from an outside source, such as a local cable system. Similarly, a corporation may have a building, or several closely spaced buildings, with numerous conference rooms equipped with television monitors and analogous program presentations may be desired. It is desirable in such a distribution system to have infrastructure which is relatively inexpensive and provides for easy expandability. Since new construction is commonly prewired by the local telephone company using category 5 twisted pair cable, a system has been developed to distribute video or other wideband signals through this existing infrastructure. Such a system is disclosed in related Patent Applications Serial Numbers 08/548,038 and

08/548,036 filed October 25, 1995 respectively by the assignee hereof.

As shown in FIGURE 1, the system consists of a distribution unit or a series of distribution units which may be cascaded to each other in a main wiring closet. These distribution units are connected via the category 5 twisted pair infrastructure to a plurality of outlets in different rooms. Each outlet may either be used as an input or an output. When used as an input, a baseband source signal such as one coming from a VCR is modulated and injected into the system through a breakout box having an enabling circuit which activates the input line. When used as an output, a television may be simply plugged into any wall outlet and tuned into the desired channel in order to receive the distributed program. This system is designed to support a plurality of channels in the frequency band of 5,75 MHz to 216 MHz.

This system provides means for modulating a baseband signal coming from, for example a VCR, as shown in Figure 1 to be transmitted on one of a plurality of channels in the frequency band 5.75 MHz to 216 MHz over the transmission path to a distribution unit for distribution to all the other outlets and cascaded distribution units in the system. Likewise, all of the modulated source signals will be distributed to all of the outlets each in different classrooms of the system.

A problem arises in that modulated signals will be attenuated over the length of the transmission path to the distribution unit, and then will be further attenuated over the transmission path from the distribution unit back to all of the outlets where monitors will display the source signal. This attenuation level will be variable and proportional to the distance between the wall outlet and the distribution unit. For example, outlets which are farther from the distribution unit will experience higher levels of attenuation then outlets which are located closer to the distribution unit. The varying levels of attenuation will result in varying signal levels at each of the outlets or monitors in the system. Because it is desirable to drive each monitor at the same signal level, the problem of varying attenuation levels depending on distance from the distribution unit must be overcome.

It is therefore an object of this invention to provide a level control system for achieving a consistent desired signal level at each of the outlets of a broadband signal distribution system where the outlets are each subject to signals having varying amounts of attenuation.

The object of this invention has been achieved by providing a cable system level control system consisting of a closed loop feedback circuit having an RF pilot detector for detecting a pilot signal generated at the distribution unit, a level control circuit, and a variable attenuator which is controlled by the level control circuit.

The invention will now be described by way of example with reference to the accompanying drawings of which:

Figure 1 shows a pictorial representation of the broadband signal distribution system.

Figure 2 shows a block diagram of bi-directional breakout box used in this system.

Figure 3 shows a block diagram of the frequency agile modulator used in this system. Figure 4 shows a high level schematic diagram of the level control system.

Figure 5 shows a schematic diagram of the pilot detector circuit used in the level control system of Figure 4. Figure 6 shows a schematic diagram of the cable system AGC drive circuit used in the system of Figure 4.

Figure 7 shows a schematic diagram of the modulator system AGC drive circuit used in the system of Figure 4.

Figure 8 shows a schematic diagram of the modulator attenuator circuit used in the system of Figure 4. Figure 9 shows a schematic diagram of the cable system attenuator interface circuit used in the system of Figure 4.

Figure 10 shows a high level schematic diagram of the cable system level control subsystem utilized in the frequency agile modulator of Figure 3.

Figure 11 shows a schematic diagram of the pilot level detector circuit used in the system of Figure 10. Figure 12 shows the AGC controller circuit used in the system of Figure 10.

Figure 13 shows a schematic diagram of the attenuator circuit used in the system of Figure 10.

The level control system of this invention consists of two level control subsystems as shown in Figures 2A and 2B. First the cable system level control subsystem 10 (Figure 2B) is designed to adjust the level of attenuation in order to compensate for the particular level of attenuation that has occurred as a result of the signal traveling from the distribution unit 38 over the transmission path 32 to the outlet 26. This circuit may be physically located for example in the breakout box 27. The modulated signal enters through an electrical connector 12 and proceeds down the RF input line 14 to a cable simulating attenuator 16. The output of the cable simulating attenuator 16 is fed into a directional coupler 18 which has two outputs 68 and 70.

The first output 70 allows the modulated signal to enter a closed feedback control loop consisting first of a bandpass filter 20 which is designed to pass a desired pilot frequency signal generated in the distribution unit 38 to an RF detector 60. The RF detector output will then drive a level control circuit 62. An attenuator control signal is generated by the level control circuit 62 and passes over output line 64 to control the cable simulating attenuators 16. The system output signal having a desired level of attenuation exits the second output 68 of the directional coupler 18 to an output connector 66 for connection to the monitor 22 of Figure 1. The attenuator control signal generated by the level control circuit 62 also controls the cable simulating attenuator 19. This cable simulating attenuator 19 is coupled to the output 94 of the modulator level control subsystem 80 and is controlled along with cable simulating attenuator 16 to achieve the same level of attenuation in each 16,19.

Referring to Figure 2A, the second level control subsystem 80 will now be described. This level control subsystem 80 is designed to achieve a desired signal level from the output of the modulator 29 (Figure 1) . Once again this circuit may be located for example in the breakout box 27 (Figure 1) . The modulated source signal enters the circuit through an electrical connector 82 and passes down the input line 84 to a series of flat response attenuators 86,88. The output of the second flat response attenuators 88 is fed to a directional coupler 90 having two outputs 92,94. The first directional coupler output 92 is fed into a closed loop feedback circuit having an RF detector 96 which detects the signal level on its input and generates a control signal which has a level proportional to the signal level on its input. The control signal is then fed to a level control circuit. An attenuator control signal is the output from the level control circuit 98 which drives each of the flat response attenuators 86,88 to achieve a desired signal level output on the directional coupler output line 94. It should be understood that while these circuits are both shown here located together in the breakout box 27, they may be located in a modulator 29 that has a fixed output signal level. An example of such an arrangement is shown in the block diagram of Figure 3. Figure 3 shows a block diagram of the frequency agile modulator as disclosed in copending U.S. Patent Application Serial No. 60/008,741 with the addition of cable system level control subsystem 10. It should be noted that the modulator level control subsystem 80 is not necessary for this particular frequency agile modulator because the modulator is designed to have a specified output signal level. In such systems as shown in Figure 1 where a modulator having a variable signal level output is utilized, then a modulator level control subsystem 80.

Referring now to Figures 4 through 9, an example of a circuit for achieving the level control subsystem 10,80 will be described in greater detail. Figure 4 shows both the cable system level control subsystem 10 (Figure 4B) and the modulator level control subsystem 80 (Figure 4A) . A modulated signal enters the cable system level control subsystem 10 through the electrical connector 12 from the distribution unit 38 (Figure 1) and travels down the input line 14 to the cable system attenuator 17. The block 17 represents both cable simulating attenuators 16,19 of Figure 2. These cable simulating attenuators 17 are controlled by the level control circuit 62 which consists of AGC shunt and series drive circuits. The pilot detector 61 receives the modulated signal from the directional coupler 18 on its output line 70. The pilot detector 61 as shown in this figure contains both the bandpass filter 20 and the RF detector 60 of Figure 2. An output signal is fed down line 63 to the level control circuit 62 which compares this output signal to a reference signal. The output signal is proportional to the signal level of the pilot signal received by the pilot detector on line 70. It should be noted that the level of the pilot signal entering line 70 will be directly proportional to the distance between the outlet 26 (Figure 1) and the distribution unit 38. This is due to the fact that the signal will experience an attenuation level which is proportional to the length of cable in the transmission path 32. Returning now to Figure 4B, the level control circuit 62 has shunt and series outputs 65,67 which comprise the attenuator control signal 69 of Figure 2B.

These outputs 65,67 are responsive to the output signal of the pilot detector 61 entering on line 63 and drive shunt and series PIN diodes which are in the cable simulating attenuators 17. Finally, the attenuated RF signal is output back to the distribution unit 38 and into the system on output line 21 through the electrical connector 12. The cable simulating attenuators 17 are provided with a test point at connector J8.

Turning now to the modulator level control subsystem 80 shown in Figure 4A, the modulated input signal enters the subsystem through the electrical connector 82 on the input line 84 which feeds the modulator attenuators 87. It should be understood that the modulator attenuators 87 shown here includes both flat response attenuators 86,88 shown in Figure 2A. The modulator controller 97 includes both the level control circuits 98 and RF detector 96 shown in Figure 2A. This controller 97 operates similar to the cable system level control circuit 62. The modulated signal is fed into the modulator controller 97 which detects the signal level and compares it to a reference signal for controlling the modulator attenuators 87. Each of the flat response PIN diode attenuators 86,88 control attenuation levels in various ranges in order to achieve attenuation of an input signal varying between 43 to 65 dbmv to achieve a constant output level of 36 dbmv on the output line 94. An example of the pilot detector circuit 61 of Figure 4B is shown in Figure 5. The RF signal is received on line 70 and enters the bandpass filter 20 which consists of an RLC circuit which passes only the pilot signal of a desired frequency. In this case, the pilot signal is at a frequency of 240 MHz. The pilot signal is then fed to the pilot detector circuit 60 which will output a DC signal proportional to the RF signal received on line 70. The DC signal is then fed to a DC amplifier U4A and the DC control signal is then fed to output line 64 to the cable system level control circuit 62. Referring to Figure 6, an example of a cable system level control circuit 62 is shown. A DC control signal enters the circuit on line 63 from the pilot detector circuit 61 of Figure 5. Two signals are generated from the DC control signal to drive the cable simulating PIN diode attenuators 17 as shown in Figure 4. A shunt control signal is provided on line 64a and a series control signal is provided on line 64b. Each of these signals drive shunt and series PIN diode attenuators 16,19 in the cable simulating attenuator circuits 17. Figure 7 shows an example of the cable simulating attenuator circuit 17 which are driven by the shunt control signal and the series control signals. These signals enter on lines 64A and 64B as shown in Figure 7A. Figure 7A shows the first cable simulating attenuator 19 which attenuates the modulated source signal coming from the modulator level control subsystem 80 as shown in Figure 2. This cable system attenuator consists of a series PIN diode U-10 and a shunt PIN diode U-ll which are controllable by the series and shunt control signals respectively. Figure 7B shows a similar PIN diode attenuator circuit having a series PIN diode U-12 in a shunt PIN diode U-13 which are controlled by the series and shunt control signals respectively. The pilot out signal coming from the capacitor C26 is fed to a directional coupler 18 as shown in Figure 2. The RF_IN_A and the RF_IN_B signals are those coming from the electrical connector 12. These are then passed through a balun circuit consisting of L7, T2, and T5 before being fed to the cable simulating attenuator 16 on line 14.

Referring to Figure 8, an example of the level control circuit 98 used in the modulator level control subsystem 80 will be described in greater detail. A modulated input signal enters the subsystem 80 on line 84 and passes through a series of flat response PIN diode attenuators 86,88 to a directional coupler 90. The output signal having a desired signal level, for example 36 dbmv, will exit the subsystem 80 on line 94.

A feedback signal is supplied from the directional coupler 90 on line 92 to the level control circuit 98. The feedback line 92 serves as an input to a broadband RF detector 96 which supplies the input signal to the level control circuit 98. Two output signals similar to those described above in Figs. 6 and 7 are supplied from the level control circuit 98 to drive both flat response PIN diode attenuators 86,88. One of the output signals 99b controls shunt PIN diodes in the attenuators and the other output signal 99a controls series PIN diodes in the attenuators . Figure 9 shows both of the modulator level control subsystem attenuator circuits 86,88 which are controlled by the level control circuit 98 of Figure 7. These circuits are similar to the attenuators 16,19 of Figure 7 described above.

Figs. 10-13 are circuit examples of the cable system level control subsystem 10 which is incorporated into a frequency agile modulator 29 of Figure 3. Figure 10 shows a high level schematic diagram of the circuit having a pilot detector, an AGC controller which consists of the level control circuits of Figure 3 and the AGC attenuators which consist of the cable simulating PIN diode attenuators of Figure 3. The operation of this circuit is the same as that of the circuit described earlier in Figure 4. Figure 11 shows an example of the pilot detector circuit used in this subsystem. Its operation likewise is the same as that of the pilot detector described earlier with reference to Figure 5. Figure 12 shows a wiring schematic of the cabling system level control circuits and is similar in operation to the circuit described earlier Figure 6. Finally, Figure 13 shows schematic diagrams of the cable simulating PIN diode attenuator circuits which are similar in operation to those described earlier with reference to Figure 7. The advantage of the modulator level control subsystem 80 is that a constant desired signal level output is provided on line 94 to the broadband distribution system when a modulated input is provided on the input 82 within the signal level range of 43 to 65 dbmv.

An advantage of the cable system level control subsystem 10 is that the modulated signals will be attenuated according to the distance between the outlet 26 and the distribution unit 38 so as to achieve a consistent desired signal level at each outlet 26 in the entire broadband distribution system of Figure 1. This is accomplished by sensing the signal level of a pilot signal of known signal strength generated at the distribution unit 38 after having traveled over the transmission path 32 to the outlet 26. The modulated signals can then be attenuated accordingly to account for the variable attenuation in the transmission paths 32.

Claims

WE CLAIM ;

1. A cable system level control system comprising: an input line connected to a first cable simulating attenuator which is variable and controllable, an output line connected to a second cable simulating attenuator which is variable and controllable, the cable second simulator being coupled to a modulated input signal. a directional coupler having one input connected to the output of the cable simulating attenuator, the directional coupler having a feedback output and a system output, a bandpass filter connected to the feedback output of the directional coupler for passing a desired pilot frequency band, an RF detector connected to the output of the bandpass filter, and; a level control circuit connected to the output of the RF detector for generating a control signal proportional to the level of the pilot band signal supplied on its input, the level control circuit being connected to control inputs of the first and second cable simulating attenuators in order to drive the attenuators for achieving a controlled signal level output on the system output of the directional coupler and the output line.

2. The cable system level control system of claim 1 wherein the level control circuit compares the pilot band signal on its input to a reference signal to produce a control signal output for driving the cable simulating attenuator.

3. The cable system level control system of claim 2 wherein the cable simulating attenuator comprises a PIN diode attenuator.

4. The cable system level control system of claim

3 wherein the PIN diode attenuator consists of a series PIN diode and a shunt PIN diode, both PIN diodes being controllable by the level control circuit.

5. The cable system level control system of claim

4 wherein the control output signal of the level control circuit consists of a shunt control signal for driving the shunt PIN diode of the PIN diode attenuator, and a series control signal for driving the series PIN diode of the PIN diode attenuator.

6. A modulator level control system comprising: a flat response attenuator having an output and an input , a second flat response attenuator having an output, and an input being connected in series with the output of the first flat response attenuator , a directional coupler connected to the output of the second flat response attenuator and having a system output and a feedback output, a broadband RF detector connected to the feedback output of the directional coupler, and; a level control circuit connected to the output of the broadband RF detector for driving control inputs of both flat response attenuators whereby a desired signal level output is achieved on the system output of the directional coupler.

7. The modulator level control system of claim 6 wherein the level control circuit compares the output of the broadband RF detector to a reference signal to produce a control signal output for driving the flat response attenuators.

8. A bi-directional breakout box for use in a wideband signal distribution system comprising: a modulator level control subsystem consisting of an input, a first flat response attenuator connected in series with a second flat response attenuator, and a feedback control circuit, for achieving a desired signal level output from the modulator control subsystem, and a cable system level control subsystem consisting of a pair of cable simulating attenuators, the first cable simulating attenuator being connected to an input from the wideband signal distribution system and the second cable simulating attenuator being connected to the output from the modulator control subsystem, each of the cable simulating attenuators being controllable by a level control feedback circuit, for sensing a pilot signal generated at a remote location in the wideband signal distribution system and driving the cable simulator attenuators according to the signal level of the pilot signal received therein.

9. The bi-directional breakout box according to claim 8 wherein the modulator level control subsystem feedback circuit further comprises: a directional coupler connected to the output of the second flat response attenuator and having a system output and a feedback output, a broadband RF detector connected to the feedback output of the directional coupler, and; a level control circuit connected to the output of the broadband RF detector for driving control inputs of both flat response attenuators whereby a desired signal level output is achieved on the system output of the directional coupler.

10. The modulator level control system of claim 9 wherein the level control circuit compares the output of the broadband RF detector to a reference signal to produce a control signal output for driving the flat response attenuators.

11. The bi-directional breakout box according to claim 8 wherein the cable system level control subsystem level control feedback circuit further comprises: an input line connected to the first cable simulating attenuator, a directional coupler having one input connected to the output of the cable simulating attenuator, the directional coupler having a feedback output and a system output, a bandpass filter connected to the feedback output of the directional coupler for passing a desired pilot frequency band, an RF detector connected to the output of the bandpass filter, and; a level control circuit connected to the output of the RF detector for generating a control signal proportional to the level of the pilot band signal supplied on its input, the level control circuit being connected to a control input of the first cable simulating attenuator and to a control input of a second cable simulating attenuator in order to drive the attenuators for achieving a controlled signal level output from each of the cable simulating attenuators.

12. The cable system level control system of claim 11 wherein the level control circuit compares the pilot band signal on its input to a reference signal to produce a control signal output for driving the cable simulating attenuators.

13. The cable system level control system of claim 12 wherein each of the cable simulating attenuators comprises a PIN diode attenuator.

14. The cable system level control system of claim

13 wherein each of the PIN diode attenuators consists of a series PIN diode and a shunt PIN diode, both PIN diodes being controllable by the level control circuit.

15. The cable system level control system of claim

14 wherein the control output signal of the level control circuit consists of a shunt control signal for driving each of the shunt PIN diodes of the PIN diode attenuators, and a series control signal for driving each of the series PIN diodes of the PIN diode attenuators .

16. A frequency agile modulator capable of modulating a baseband signal to a desired frequency channel and having a fixed signal level output comprising:

A cable system level control system having an input line for receiving the fixed level output being connected to a cable simulating attenuator, a directional coupler having one input connected to the output of the cable simulating attenuator, the directional coupler having a feedback output and a system output, a bandpass filter connected to the feedback output of the directional coupler for passing a desired pilot frequency band, an RF detector connected to the output of the bandpass filter, and; a level control circuit connected to the output of the RF detector for generating a control signal proportional to the level of the pilot band signal supplied on its input, the level control circuit being connected to a control input of the cable simulating attenuator in order to drive the attenuator for achieving a controlled signal level output on the system output of the directional coupler.

17. The cable system level control system of claim

16 wherein the level control circuit compares the pilot band signal on its input to a reference signal to produce a control signal output for driving the cable simulating attenuator.

18. The cable system level control system of claim

17 wherein the cable simulating attenuator comprises a PIN diode attenuator.

19. The cable system level control system of claim

18 wherein the PIN diode attenuator consists of a series PIN diode and a shunt PIN diode, both PIN diodes being controllable by the level control circuit.

20. The cable system level control system of claim

19 wherein the control output signal of the level control circuit consists of a shunt control signal for driving the shunt PIN diode of the PIN diode attenuator, and a series control signal for driving the series PIN diode of the PIN diode attenuator.