Radio frequency amplifier and automatic gain control system and automatic gain control method

Abstract

Automatic gain control can be implemented in a radio frequency amplifier in a hybrid fiber coax network using a wideband radio frequency tuner to select a plurality of pilot channels (e.g., frequencies of lower and higher portions of a radio frequency signal) for measuring power and determining a correction to apply to the radio frequency amplifier. The power of one or more pilot channels can be measured using a received signal strength indicator from the wideband radio frequency tuner or using a power detector circuit. Using a wideband radio frequency tuner allows selectable gain and / or tilt control over a wide frequency spectrum to maintain a stable radio frequency output level from the amplifier as the radio frequency input level varies. The radio frequency amplifier can be a line extension amplifier used in a community antenna television hybrid fiber coax network to amplify a wideband radio frequency spectrum up to 1.8 GHz.

Description

TECHNICAL FIELD

[0001] The present disclosure relates to radio frequency (RF) amplifiers, and more particularly, to automatic gain control using wideband RF tuners in radio frequency amplifiers in hybrid fiber coaxial (HFC) networks, such as community antenna television (CATV) networks. BACKGROUND

[0002] Radio frequency amplifiers are used to amplify radio frequency signals in communication systems, such as community antenna television (CATV) systems that provide downstream (forward) signals to subscriber locations and upstream (reverse) signals from subscriber locations. In a hybrid fiber coaxial (HFC) network that provides community antenna television (CATV) service, optical communication is provided between a headend / Hub and an optical node over an optical fiber, and electrical radio frequency communication is provided between the optical node and the subscriber locations over coaxial cables. In such hybrid fiber coaxial (HFC) networks, radio frequency amplifiers are used after the optical node to extend the transmission distance of the radio frequency signals, thereby extending the range of the community antenna television (CATV) service provided to the subscriber locations.

[0003] Cable companies increase the capacity of their networks (adding more television channels or more Internet bandwidth capacity) by increasing the frequency range of the radio frequency network. As the radio frequency cable plant frequency range expands to higher frequencies, cable loss increases. Therefore, the gain or output level of the radio frequency amplifiers needs to be increased to maintain the required signal level in the network. One of the challenges faced by expanding data and communication networks is to update the radio frequency amplifiers to operate at increased gain / output level over a higher frequency range without requiring major changes to the hybrid fiber coaxial network infrastructure (e.g., moving the radio frequency amplifiers in the hybrid fiber coaxial network closer to each other). In addition to providing the required gain, the radio frequency amplifiers should also account for changes in network frequency tilt, which can have a large impact given the non-linear characteristics of the response of the coaxial cable at higher frequencies. Maintaining a stable radio frequency output level of the amplifiers at higher frequencies over a wider radio frequency spectrum is particularly challenging in designing higher bandwidth radio frequency amplifiers to meet the higher bandwidth community antenna television / hybrid fiber coaxial (CATV / HFC) network requirements, as the input level varies due to changes caused by temperature. SUMMARY

[0004] According to one embodiment, a controlled radio frequency (RF) amplifier is provided for use in a hybrid fiber-coaxial (HFC) network. The controlled RF amplifier includes amplifier circuitry for receiving an input downstream RF signal having a wide spectrum and amplifying the input downstream RF signal to provide an output downstream RF signal having a wide spectrum. The controlled RF amplifier also includes automatic gain control (AGC) circuitry for controlling the gain of the amplifier circuitry. The AGC circuitry includes a wideband RF tuner for receiving samples of the downstream RF signal from the amplifier circuitry and selecting at least first and second pilot channels from the downstream RF signal. The samples of the downstream RF signal can be obtained at the input, immediate stage, output, or any other location within the controlled RF amplifier. The AGC circuitry also includes a power detector circuitry or a received signal strength indicator (RSSI) signal monitoring circuitry for measuring the power of at least the first and second pilot channels, and a controller for determining a correction based on the measured power of at least the first and second pilot channels, and providing one or more control voltages to the amplifier circuitry based on the correction.

[0005] According to another embodiment, an automatic gain control (AGC) system is provided for controlling the gain of a radio frequency (RF) line extender amplifier in a hybrid fiber-coaxial (HFC) network. The automatic gain control system includes a broadband RF tuner for receiving samples of a downstream RF signal from the RF amplifier and selecting at least first and second indexing channels from the downstream RF signal. The downstream RF signal has a broadband spectrum up to 1.8 GHz, wherein the first channel is located in the lower frequency range of the broadband spectrum and the second channel is located in the higher frequency range of the broadband spectrum. The automatic gain control system further includes a power detector circuit for measuring the power of the selected at least first and second indexing channels, and a controller for determining a correction based on the measured power of the at least first and second indexing channels and providing a control voltage to the RF amplifier according to the automatic gain control correction.

[0006] According to another embodiment, a method is provided for providing automatic gain control (AGC) of a radio frequency (RF) amplifier in a hybrid fiber-coaxial (HFC) network. The method includes: receiving an input downstream RF signal having a wideband RF spectrum in the RF amplifier; amplifying the input downstream RF signal using RF amplifier circuitry to generate an output downstream RF signal having a wideband RF spectrum; selecting at least first and second indexing channels in the downstream RF signal having a wideband spectrum, wherein the selection of indexing channels is performed using a wideband RF tuner; measuring the power of at least the first and second indexing channels; determining a correction at least in part based on the measured power of the first and second indexing channels; and sending a control voltage to the RF amplifier circuitry according to the correction. Attached Figure Description

[0007] These and other features and advantages will be better understood by reading the following detailed description in conjunction with the accompanying drawings, in which:

[0008] Figure 1 This is a schematic diagram of a public antenna television network according to an embodiment of the present disclosure, including a radio frequency (RF) line extension amplifier with an automatic gain control (AGC) system, wherein the automatic gain control system uses a wideband RF tuner to select multiple lead channels for automatic gain control;

[0009] Figure 2 This is a schematic diagram of an RF amplifier according to an embodiment of the present disclosure, including an automatic gain control system for controlling the gain of a downstream or forward RF signal based on an cipher channel selected by a broadband RF tuner.

[0010] Figure 3 This is a schematic diagram of an embodiment of an adjustable automatic gain control system, including a broadband radio frequency tuner for selecting a lead channel and a power detector circuit for measuring the power of the selected lead channel.

[0011] Figure 4 This is a schematic diagram of another embodiment of an adjustable automatic gain control system, including a broadband radio frequency tuner for selecting a trigger channel and using a signal strength pointer to measure the power of the selected trigger channel.

[0012] Figure 5 This is a schematic diagram of an embodiment of an adjustable automatic gain control system, including a broadband radio frequency tuner for selecting an index channel in the lower and higher portions of the spectrum, and a block conversion circuit for moving a higher frequency in the higher portion of the spectrum into the range of the radio frequency tuner.

[0013] Figure 6This is a schematic diagram of another embodiment of an adjustable automatic gain control system, including a broadband radio frequency tuner for selecting an index channel in the lower and higher portions of the spectrum, and a block switching circuit for moving a higher frequency in the higher portion of the spectrum into the range of the radio frequency tuner.

[0014] Figure 7 This is a schematic diagram of another embodiment of an adjustable automatic gain control system, including a broadband radio frequency tuner for selecting index channels in the lower and higher portions of the spectrum, and a block switching circuit for shifting higher frequencies in the higher portion of the spectrum into the range of the radio frequency tuner; and

[0015] Figure 8 This is a flowchart illustrating one embodiment of a method for providing automatic gain control (AGC) of a radio frequency amplifier by selecting an indicative channel.

[0016] [Explanation of Labels in the Attached Image]

[0017] 100: Public Antenna Television Network

[0018] 110: Header / Hub

[0019] 111: Forward Path Fiber

[0020] 112: Fiber Optic Repeater

[0021] 113: Reverse path fiber

[0022] 114: Optical Node

[0023] 115: Coaxial cable

[0024] 116: Coaxial cable distribution network

[0025] 117: Tap Connector

[0026] 118: Client device

[0027] 119: Line Extension RF Amplifier

[0028] 200: Radio Frequency Amplifier

[0029] 202: First Port

[0030] 204: Second Port

[0031] 206: Positive signal

[0032] 208: Reverse signal

[0033] 212: Forward Test Point Circuit

[0034] 214: Reverse Test Point Circuit

[0035] 222: First Duplex Filter

[0036] 224: Second Duplex Filter

[0037] 232, 234: Directional Couplers

[0038] 242: Positive Gain Stage

[0039] 244: Inverting gain stage

[0040] 250: Automatic Gain Control System

[0041] 252, 352, 452, 552: Wideband RF tuners

[0042] 300, 400: Amplifier circuit

[0043] 306a, 306b, 406a, 406b: Downstream RF signals

[0044] 340, 440: Gain Stage

[0045] 342,442: Variable tilt compensation network

[0046] 350, 450: Automatic Gain Control System

[0047] 354,554: Power detector circuit

[0048] 356, 456, 556: Controller

[0049] 506: Radio Frequency Signal

[0050] 508: Automatic Gain Control Coupler

[0051] 560,560',560”: Block switching circuit

[0052] 561: Attenuator

[0053] 562: Separator

[0054] 563: High-pass filter

[0055] 564: Mixer

[0056] 565: Local Oscillator

[0057] 566, 567: Low-pass filter

[0058] 568: Switch

[0059] 569: Bandpass filter

[0060] 800: Method

[0061] 810-820: Steps Detailed Implementation

[0062] Automatic gain control (AGC) can be implemented in the radio frequency (RF) amplifier in a hybrid fiber-coaxial (HFC) network. Consistent with embodiments of this disclosure, a wideband RF tuner is used to select multiple index channels (e.g., frequencies of the lower and higher portions of the RF signal spectrum) for power measurement and to determine the correction to be applied to the RF amplifier. Power can be measured, for example, using a Received Signal Strength Indicator (RSSI) from the wideband RF tuner or using a power detector circuit following the wideband RF tuner. Using a wideband RF tuner allows for selectable gain and / or tilt control over a wideband spectrum (e.g., the channel spectrum of a downstream RF signal in a public antenna television network) to maintain a stable RF output level when RF amplifier performance or input level varies due to factors such as higher frequency operation or temperature-induced variations. In the embodiments described herein, the RF amplifier is a line extension amplifier for amplifying a wideband RF spectrum up to 1.8 GHz in a public antenna television hybrid fiber-coaxial network; however, the automatic gain control system and method using a wideband RF tuner described herein can be used in hybrid fiber-coaxial networks and other types of RF amplifiers across other frequency ranges.

[0063] As used herein, a “channel” refers to a frequency subrange within a frequency spectrum that can be modulated to carry a message. A “channel” can be identified as a single frequency within a frequency subrange, and as used herein, “selecting a channel” can include selecting a single frequency that identifies the channel. As used herein, a “downstream RF signal” (also known as a forward RF signal) is an RF signal transmitted from a source, such as a public antenna television headend / hub, to a destination, such as a public antenna television subscriber. As used herein, “composite power” refers to the total power from multiple frequencies of an RF signal. As used herein, a “channel spectrum” refers to a predefined frequency modulation range that is divided into multiple frequency subranges (called physical channels) and can be modulated to carry a message. A “public antenna television channel spectrum” is the channel spectrum used to transmit video and / or data in a public antenna television network and is not limited to a specific frequency range.

[0064] As used herein, “module” is a structural term referring to a separate assembly of elements (e.g., electronic, optical, or optoelectronic elements) that together perform a specific function. The “module” discussed herein (e.g., optical receiver module and RF amplifier module) is used as a structural name, and therefore the term “module” is not used as a nonce word in this application. As used herein, the term “circuit” refers to physical electronic components (i.e., hardware) and any software and / or firmware (i.e., program code) that can configure, be executed by, and / or otherwise associate with hardware. For example, a particular processor and memory may include a first “circuit” when executing a first portion of program code to perform a first function, and a second “circuit” when executing a second portion of program code to perform a second function. As used herein, the term “coupling” refers to any connection, coupling, link, etc., between elements. Such “coupled” elements are not necessarily directly connected to each other and may be separated by intermediate components.

[0065] Please refer to Figure 1 This section describes in more detail an example of a public antenna television network 100 implementing automatic gain control (AGC) using a broadband radio frequency tuner according to embodiments of the present disclosure. The automatic gain control system and method using a broadband radio frequency tuner can be implemented, for example, in a line extension radio frequency amplifier 119 within the public antenna television network 100, as described in more detail below. Generally, the public antenna television (CATV) network 100 is a hybrid fiber-coaxial (HFC) network capable of delivering cable television programming (i.e., video) and Internet Protocol address data services (e.g., Internet and Voice over IP) to customers or subscribers 102 via the same fiber optic cable and coaxial cable (i.e., trunk line). Such a public antenna television (CATV) network 100 is typically used by service providers such as Comcast to provide subscribers 102 with combined video, voice, and broadband network services. Although exemplary embodiments of a public antenna television (CATV) network are described herein based on various standards (e.g., the Data-Over-Cable Service Interface Specification or the Data-Over-Cable Service Interface Specification (DOCSIS)), the concepts described herein are applicable to other embodiments of public antenna television (CATV) networks using other standards.

[0066] Multiple cable television channels and Internet Protocol address (IPA) data services (e.g., broadband networks and IPA voice) can be simultaneously transmitted in a public antenna television network 100 using frequency division multiplexing (FDM) transmission signals on multiple physical channels in the public antenna television channel spectrum. An example of the public antenna television downstream channel spectrum (also known as the forward spectrum) includes channels from 650 MHz to 1794 MHz, but the public antenna television channel spectrum can be further extended to increase the bandwidth available for data transmission. Within the public antenna television channel spectrum, some physical channels can be allocated to cable television channels, while others can be allocated to IPA data services. Other channel spectrum and bandwidth can also be used and are within the scope of this disclosure.

[0067] In addition to transmitting signals downstream (also known as forward signals) to deliver video and Internet Protocol address data to subscriber 102, the public antenna television network 100 can also carry signals from upstream of the subscriber (such as Internet Protocol address data or control signals) (also known as reverse signals), thereby providing bidirectional communication via a trunk. According to one example, the signal spectrum of the reverse signal carried upstream can be as high as 600 MHz.

[0068] A public antenna television network 100 typically includes a headend / hub 110 connected via fiber optic trunk 112 to one or more optical nodes 114, which in turn are connected via a coaxial cable distribution network 116 to customer premises equipment (CPE) 118 at subscriber location 102. The headend / hub 110 receives, processes, and combines content (e.g., broadcast video, narrowcast video, and Internet data) as optical signals for transmission via the fiber optic trunk 112. The fiber optic trunk 112 includes a forward path fiber 111 for transmitting downstream optical signals from the headend / hub 110 and a return or reverse path fiber 113 for transmitting upstream optical signals back to the headend / hub 110. The optical nodes 114 provide an optical-to-electrical interface between the fiber optic trunk 112 and the coaxial cable distribution network 116. Therefore, optical node 114 receives downstream optical signals and transmits upstream optical signals, and transmits downstream (forward) radio frequency signals and receives upstream (reverse) radio frequency signals.

[0069] The coaxial cable distribution network 116 includes coaxial cable 115, which includes a relay coaxial cable connected to optical node 114 and a feed coaxial cable connected to the relay coaxial cable. Subscriberdrop coaxial cables are connected to the distribution coaxial cable using a tap 117 and to client equipment 118 at subscriber location 102. Client equipment 118 may include set-top boxes for video and a modem for data. One or more line extension RF amplifiers 119 may also be coupled to coaxial cable 115 for amplifying positive signals (e.g., CATV signals) transmitted downstream to subscriber 102 and for amplifying reverse signals transmitted upstream from subscriber 102. In this embodiment, line extension RF amplifiers 119 may include an automatic gain control (AGC) system using a broadband RF tuner for controlling the gain of at least the downstream or positive RF signals, as described herein. In other embodiments, the systems and methods for automatic gain control using a broadband RF tuner can be used in other RF amplifiers.

[0070] Please refer to Figure 2 The diagram illustrates and describes in more detail an RF amplifier 200 including automatic gain control (AGC) using a wideband RF tuner to select the indicative channel. In one example, the controlled RF amplifier 200 may be a line extension amplifier supporting DOCSIS 4.0 FDD (frequency division duplex) capability, with downstream operating frequencies up to 1794 MHz and upstream operating frequencies up to 684 MHz. Frequency division duplex refers to bidirectional wideband RF communication where downstream and upstream each have their own dedicated, non-overlapping spectrum. The RF amplifier 200 may be a line extension RF amplifier, such as the line extension RF amplifier 119 used in the aforementioned public antenna television network 100.

[0071] The RF amplifier 200 includes at least first and second ports 202, 204 for coupling to electrical paths transmitting forward and reverse (RF) signals 206, 208, such as a coaxial cable 115 transmitting RF signals downstream and reverse RF signals upstream in a public antenna television network 100. The RF amplifier 200 may be located within an amplifier housing 201, such as a weatherproof housing configured for outdoor environments, with the first and second ports 202, 204 located outside the amplifier housing 201. The first port 202 provides an input for the forward signal 206 and an output for the reverse signal 208, and the second port 204 provides an input for the reverse signal 208 and an output for the forward signal 206. The RF amplifier 200 may include forward and reverse test point circuits 212, 214 coupled to the respective first and second ports 202, 204 via corresponding directional couplers 232, 234. Forward and reverse test point circuits 212, 214 allow for testing of forward and reverse signals 206, 208 before and after amplification, for example as described in U.S. Patent No. 6,769,133, which is incorporated herein by reference in its entirety.

[0072] The RF amplifier 200 further includes a first duplex filter 222 coupled to a first port 202, a second duplex filter 224 coupled to a second port 204, and forward and reverse gain stages 242 and 244 coupled between the first and second duplex filters 222 and 224. The first and second duplex filters 222 and 224 separate the forward and reverse signals propagating on the same electrical path at the first and second ports 202 and 204. The first duplex filter 222 separates and transmits the forward signal 206 received at the first port 202 for amplification via the forward gain stage 242, and the second duplex filter 224 separates and transmits the reverse signal 208 received at the second port 204 for amplification via the reverse gain stage 244. The duplex filters and gain stages can be implemented using known circuit components in RF amplifiers. The RF amplifier 200 may also include other circuit components (not shown), such as attenuators, equalizers, high-pass filters, low-pass filters, system trimming circuitry, and inverse 6 dB switching circuitry.

[0073] In this example, the automatic gain control (AGC) system 250 is coupled at least to the positive gain stage 242 of the amplified positive (downstream RF) signal 206. The AGC system 250 provides automatic gain control (AGC) and / or automatic level / slope control (ALSC) based on selected index channels in the positive (downstream RF) signal 206. The AGC or ALSC is used to maintain a stable RF output level of the positive (amplifier) ​​gain stage 242 in the event of RF input level variations (e.g., due to temperature variations and coaxial and passive losses). As will be described in more detail below, the AGC system 250 uses a wideband RF tuner 252 to select multiple index channels (also called test channels) from a sample of the downstream or positive (RF) signal 206 and determine appropriate gain and / or slop compensation. The AGC system 250 can sample the positive (downstream RF) signal 206 at the input, direct stage, output, or any other location within the controlled RF amplifier 200.

[0074] Please refer to Figure 3 An embodiment of the amplifier circuit 300 and the automatic gain control system 350 is shown in more detail. The amplifier circuit 300 is used to receive the input downstream RF signal 306a and amplify the input downstream RF signal 306a to provide an amplified output downstream RF signal 306b. In one example, the operating gain of 1794MHz can be in the range of 46 to 50 dB. In this embodiment, the amplifier circuit 300 includes a gain stage 340 to provide amplification over a wideband RF spectrum and a variable tilt compensation network 342 to provide tilt compensation over a wideband RF spectrum. The variable tilt compensation network 342 may include attenuators and / or equalizers, such as those known to those skilled in the art for automatic gain control and / or automatic level / slope control, to correct for frequency response shifts with temperature. The attenuator may include, for example, a variable attenuator, such as an adjustable pad with a flat response. The equalizer may include a variable equalizer with a tilt response, such as a flat or linear tilt response or a bow or cable tilt response.

[0075] The automatic gain control system 350 includes a wideband RF tuner 352, a power detector circuit 354, and a controller 356, such as a microcontroller. The wideband RF tuner 352 may include a commercial terrestrial television tuner, such as the Si2141 tuner available from Skyworks Solutions or the MXL608 tuner available from MaxLinear. The wideband RF tuner 352 receives a portion or sample of downstream RF signals 306a, 306b and selects a lead channel for automatic gain control. Although the illustrated embodiment shows a sample acquired at the output, samples of the downstream RF signals 306a, 306b may be acquired at the input, direct stage, output, or any other location within the controller's RF amplifier. In one example, the wideband RF tuner 352 selects a first lead channel (i.e., a lower lead channel) in the lower portion of the RF spectrum frequency range and a second lead channel (i.e., a higher lead channel) in the higher portion of the RF frequency range. For example, in an embodiment of a 1.8 GHz RF amplifier with a forward band or RF spectrum frequency range of 54 MHz to 1.8 GHz, the lower indexing channel may be below 750 MHz, while the higher indexing channel may be above 1.2 GHz. In one embodiment of a 1.2 GHz RF amplifier with a forward band of 54 MHz to 1.2 GHz, the lower indexing channel may be below 500 MHz, while the higher indexing channel may be above 700 MHz.

[0076] The indexing channels for the broadband RF tuner 352 can be selected based on amplifier configuration or user input. For example, the number and / or location of indexing channels can be set according to the amplifier's operating frequency range or set to specific customer-defined locations. This flexibility in the broadband tuner's indexing channel location allows for adjustment of automatic gain control operation as the positive bandwidth changes. In some embodiments, lower indexing channels or frequencies may be older indexing channels, and higher indexing channels or frequencies may be the highest channels in use. Selecting more than two indexing channels and / or selecting indexing channels over a wider frequency range can, for example, allow for more accurate tilt compensation to compensate for nonlinear tilt in coaxial cables.

[0077] The power detector circuit 354 provides a detector voltage derived from the signal level of the selected priming channel selected and passed to it by the broadband tuner. When using multiple priming channels, the power detector circuit 354 measures the power of each channel separately and generates a detector voltage for each channel. The power detector circuit 354 may include known power detector circuits, such as the LMH2110 available from TI or the LT5537 available from Linear Technologies.

[0078] Controller 356 receives individual trigger channel power measurements from power detector circuit 354 and determines the desired amplifier correction based on those measurements and / or user input. Controller 356 then generates the required control voltage or multiple voltages to be applied to amplifier circuit 300 for automatic gain control purposes. The gain and / or tilt of amplifier circuit 300 is adjusted in response to one or more control voltages to achieve amplifier correction. Controller 356 may include a microcontroller, such as the STM32G0B1RCT6 available from ST Microelectronics. Controller 356 is capable of receiving user input including automatic gain control parameters such as target gain and target tilt.

[0079] To adjust the tilt, controller 356 can sense changes in response level at various frequencies (e.g., multiple indexing channels) and adjust the variable attenuator and / or equalizer to compensate for the tilt (e.g., to achieve a user-defined target tilt). A user can access controller 356 (e.g., via application software) and instruct it to change the variable attenuator and / or equalizer as needed. For example, if a user examines the input test points in an RF amplifier and determines that the attenuator and / or equalizer needs adjustment, the user can access controller 356 to make that adjustment. The user can also instruct controller 356 to set the amplifier to a predetermined configuration, and controller 356 will follow an algorithm to complete the user configuration.

[0080] Please refer to Figure 4 Another embodiment of the amplifier circuit 400 and the automatic gain control system 450 is shown and described in more detail. Similar to the embodiment described above, the amplifier circuit 400 includes a gain stage 440 to provide gain and a variable tilt compensation network 442 to provide tilt compensation over a wideband radio frequency spectrum. In this embodiment, the automatic gain control system 450 also includes a wideband radio frequency tuner 452 to select a trigger channel, but uses an RSSI (Received Signal Strength Indication) signal 454 from the wideband radio frequency tuner 452 instead of a power detector circuit to provide a signal level indication for the selected trigger channel. A controller 456, such as a microcontroller, can then generate an automatic gain control control voltage or multiple control voltages derived from the RSSI signal 454 of each tuned trigger channel for adjusting the gain and / or tilt in the amplifier circuit 400. In this embodiment, the controller 456 or a separate received signal strength indication monitoring circuit can be used to receive the RSSI signal 454.

[0081] In both embodiments, the automatic gain control systems 350 and 450 can also be used to prevent the automatic gain control from railing the amplifier to a full-gain state due to RF signal loss at the selected lead channel. For example, the wideband RF tuners 352 and 452 can be used to select a different lead channel if signal loss is detected at a previously selected lead channel. If first and second lead channels in a lower and higher frequency range are used, different lead channels can be selected in the respective lower and higher frequency ranges. In other embodiments, the automatic gain control systems 350 and 450 can be used to revert to thermistor-based gain control, where the gain is adjusted in response to thermal measurements. In yet another embodiment, the automatic gain control systems 350 and 450 can be used to lock the gain setting at the level or state prior to RF signal loss at the selected lead channel.

[0082] In some embodiments, a broadband radio frequency tuner (e.g., a terrestrial television tuner) may not be able to select an index channel at a higher forward band frequency supported by the radio frequency amplifier. For example, some television tuners may only operate at frequencies up to 1.0 GHz, while newer radio frequency amplifiers have a forward band up to 1.8 GHz. In these embodiments, the automatic gain control system may also include block switching circuitry to shift higher frequencies down to lower frequencies within the broadband tuner's range, as will be described in more detail below.

[0083] Figures 5 to 7 Different embodiments of block switching circuits 560, 560', 560" that can be used in the automatic gain control system described above are shown. In the embodiments shown, the block switching circuits 560, 560', 560" discussed above are used in the automatic gain control system described above. Figure 3 Similarly, the automatic gain control system includes a broadband radio frequency tuner 552 for selecting a lead channel, a power detector 554 for measuring the power of the selected lead channel, and a controller 556 (e.g., a microprocessor) for providing automatic gain control control signals to amplifier circuitry (e.g., a variable attenuator and an equalizer).

[0084] like Figure 5As shown, an automatic gain control coupler 508 can be used to guide a sample of the RF signal 506 into the automatic gain control circuitry. An attenuator 561 can be used to attenuate the sampled RF signal, and a splitter 562 separates the sampled RF signal and routes it to low-frequency and high-frequency paths. The low-frequency path includes a low-pass filter 567 and allows RF signals within the range of the wideband RF tuner 552 to pass through. The high-frequency path includes a high-pass filter 563 to allow RF signals outside the range of the RF tuner 552 to pass through. The high-frequency path block uses a mixer 564 to convert those RF signals above the tuning range of the RF tuner 552 to lower frequencies within the range of the wideband RF tuner 552. The mixer 564 is coupled to a local oscillator 565, followed by a low-pass filter 566.

[0085] A switch 568, such as a single-pole double-throw (SPDT) switch, selects at any given time which of the two paths to route to the wideband RF tuner 552. The wideband RF tuner 552 selects a specific lead channel and converts it to an intermediate frequency (IF) channel, which is filtered by a bandpass filter 569 and sent to a power detector 554. The power detector 554 measures the level of the IF channel and outputs a voltage representing that level. This process can be repeated at different points throughout the RF signal band to select additional lead channels. The controller 556 then uses the power level information from the power detector 554 and other information programmed into the controller 556 to determine the necessary corrections in the amplifier circuitry, such as determining which variable attenuators and / or equalizers to adjust and by how much.

[0086] Figure 6 The embodiment of the block switching circuit 560' shown is similar to Figure 5 However, the positions of splitter 562 and switch 568 have been reversed to improve path isolation and provide better termination within the circuit. Low-pass filter 566 has also been moved to the common signal path after splitter 562 to eliminate the need for multiple low-pass filters. Figure 7 The embodiment of the block conversion circuit 560 shown is similar to Figure 6 However, using a second switch 568b (e.g., an SPDT switch) instead of a decoupler provides better path isolation.

[0087] If necessary, other variations of the block switching circuit can be used to shift higher frequencies into the range of the broadband RF tuner. In other embodiments, the broadband RF tuner may be a channel capable of selecting higher frequencies of the RF amplifier, and the block switching circuit may not be required.

[0088] Please refer to Figure 8This document illustrates and describes a method 800 for providing automatic gain control of a radio frequency (RF) amplifier in a hybrid fiber-coaxial network, consistent with this disclosure. This method can be performed using any embodiment of the automatic gain control system described above. According to method 800, an input downstream RF signal having a wide RF spectrum (e.g., 1.8 GHz) is received in an RF amplifier, such as a line extender RF amplifier in a hybrid fiber-coaxial network (step 810). The input downstream RF signal is amplified in the amplifier to produce an output downstream RF signal having a wide RF spectrum (step 812). Amplifying the RF signal may include increasing the operating gain at 1794 MHz, for example, in the range of 46 to 50 dB.

[0089] As described above, at least first and second lead channels in the downstream RF signal are selected using a broadband RF tuner (step 814), for example, upper and lower lead channels. The power of at least the first and second lead channels is measured (step 816), for example, using a power detector circuit or RSSI circuit in the broadband RF tuner. A correction is then determined at least in part based on the measured power of at least the first and second lead channels (step 818), and one or more control voltages are sent to the amplifier circuitry, for example, a variable tilt compensation network and / or gain stage, based on this correction (step 820). The RF amplifier gain and / or tilt are adjusted in response to the one or more control voltages determined from the measured power of the selected at least the first and second lead channels.

[0090] Therefore, using a wideband RF tuner to select the trigger channel for automatic gain control on the wideband RF spectrum (e.g., 1.8 GHz) avoids the need to reposition RF amplifiers in hybrid fiber-coaxial networks and allows RF amplifiers in hybrid fiber-coaxial networks (e.g., public antenna television networks) to maintain a stable RF output level when RF amplifier performance and / or input levels change (e.g., due to temperature variations). The wideband RF tuner also supports an adjustable automatic gain control system, which helps users configure and adjust the desired gain and / or tilt, for example, to address variations in the positive band of the RF signal and the nonlinear frequency response of the coaxial cable.

[0091] While the principles of the invention have been described herein, it should be understood by those skilled in the art that this description is by way of example only and not as a limitation on the scope of the invention. Other embodiments are contemplated within the scope of the invention, in addition to the exemplary embodiments shown and described herein. Modifications and substitutions made by those skilled in the art are considered to be within the scope of the invention.

Claims

1. A controlled radio frequency (RF) amplifier for use in a hybrid fiber coaxial (HFC) network, the controlled RF amplifier comprising: an amplifier circuit for receiving an input downstream RF signal having a wideband RF spectrum and amplifying the input downstream RF signal to provide an output downstream RF signal having the wideband RF spectrum; an automatic gain control (AGC) circuit for controlling a gain of the amplifier circuit, the AGC circuit comprising: a wideband RF tuner for receiving a sample of the downstream RF signal from an output of the amplifier circuit and selecting at least first and second pilot channels from the sample of the downstream RF signal; means for measuring power of the at least first and second pilot channels; and a controller for determining a correction based on the power of the at least first and second pilot channels and providing a control voltage or voltages to the amplifier circuit based on the correction.

2. The controlled RF amplifier of claim 1, wherein the wideband RF tuner is for receiving a sample of the downstream RF signal at an output of the amplifier circuit.

3. The controlled RF amplifier of claim 1, wherein the amplifier circuit comprises a variable tilt compensation network, and wherein the correction comprises a gain correction and a tilt compensation.

4. The controlled RF amplifier of claim 1, wherein the wideband RF tuner is for selecting the first pilot channel in a lower portion of the wideband RF spectrum and for selecting the second pilot channel in an upper portion of the wideband RF spectrum.

5. The controlled RF amplifier of claim 4, wherein the controlled RF amplifier is for amplifying the downstream RF signal at frequencies up to 1.8 GHz, and wherein the first pilot channel is below 750 MHz and the second pilot channel is above 1.2 GHz.

6. The controlled RF amplifier of claim 4, wherein the wideband RF spectrum of the downstream RF signal is up to 1.2 GHz, and wherein the first pilot channel is below 500 MHz and the second pilot channel is above 700 MHz.

7. The controlled RF amplifier of claim 1, wherein the controlled RF amplifier is for use as a line extension amplifier at a feeder of the HFC network.

8. The controlled RF amplifier of claim 1, wherein the controlled RF amplifier supports DOCSIS 4.0 FDD (frequency division duplexing) capability.

9. The controlled RF amplifier of claim 1, wherein the means for measuring power comprises the wideband RF tuner providing a received signal strength indicator (RSSI) indicative of the power.

10. The controlled RF amplifier of claim 1, wherein the means for measuring power comprises a power detector circuit after the wideband RF tuner.

11. The controlled RF amplifier of claim 1, wherein the wideband RF tuner is for selecting the at least first and second pilot channels in response to user input. ​ 12. The controlled RF amplifier of claim 1, wherein the wideband RF tuner is configured to receive a user selection of a number and location of the pilot channels.

13. The controlled RF amplifier of claim 1, wherein the controller is configured to receive a plurality of automatic gain control parameters.

14. The controlled RF amplifier of claim 1, wherein the wideband RF tuner is a terrestrial TV tuner, and wherein the AGC circuit further comprises a block conversion circuit configured to down-convert high frequencies of the downstream RF signal to low frequencies within a range of the terrestrial TV tuner.

15. An automatic gain control (AGC) system for controlling gain in an RF amplifier in a hybrid fiber coaxial (HFC) network, the AGC system comprising: a wideband RF tuner configured to receive an output downstream RF signal from the RF amplifier and select at least first and second pilot channels from a sample of the downstream RF signal, wherein the downstream RF signal has a wide frequency spectrum up to 1.8 GHz, wherein the first pilot channel is located in a lower frequency range of the wide frequency spectrum, and wherein the second pilot channel is located in a higher frequency range of the wide frequency spectrum; a power detector circuit configured to measure power of the selected at least first and second pilot channels; and a controller configured to determine a correction based on the measured power of the at least first and second pilot channels and provide a control voltage or voltages to the RF amplifier in accordance with the correction for automatic gain control.

16. The AGC system of claim 15, wherein the wideband RF tuner is a terrestrial TV tuner, and further comprising a block conversion circuit configured to down-convert high frequencies of the downstream RF signal to low frequencies within a range of the terrestrial TV tuner.

17. A method for providing automatic gain control (AGC) of a radio frequency (RF) amplifier in a hybrid fiber coaxial (HFC) network, the method comprising: receiving an input downstream RF signal having a wideband RF spectrum in the RF amplifier; amplifying the input downstream RF signal using an RF amplifier circuit to produce an output downstream RF signal having the wideband RF spectrum; selecting at least first and second pilot channels from a sample of the downstream RF signal having the wideband RF spectrum at a location in the RF amplifier, wherein selecting the at least first and second pilot channels is performed using a wideband RF tuner; measuring power of the at least first and second pilot channels; determining a correction based at least in part on the measured power of the first and second pilot channels; and sending a control voltage or voltages to the RF amplifier circuit in accordance with the correction.

18. The method of claim 17, wherein the correction comprises a gain correction and a tilt compensation.

19. The method of claim 17, wherein the first pilot channel is located in a lower portion of the wideband RF spectrum, and wherein the second pilot channel is located in a higher portion of the wideband RF spectrum.

20. The method of claim 19, wherein the wideband RF spectrum of the downstream RF signal is up to 1.8 GHz, and wherein the first pilot channel is below 750 MHz and the second pilot channel is above 1.2 GHz.

21. The method of claim 19, wherein the wideband RF spectrum of the downstream RF signal is up to 1.2 GHz, and wherein the first pilot channel is below 500 MHz and the second pilot channel is above 700 MHz.

22. The method of claim 17, wherein the power is measured using a power detector circuit after the wideband RF tuner.

23. The method of claim 17, further comprising receiving a user selection of at least one of the first and second pilot channels.

24. The method of claim 17, further comprising receiving a user selection of a number and location of the pilot channels.

25. The method of claim 17, further comprising receiving user input of at least one automatic gain control parameter selected from the group consisting of target gain and target tilt.

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