System and method for coarse/fine PLL adjustment

#This application relates generally to receiver circuits and, in particular to a CATV tuner with a frequency plan and architecture that allows the entire receiver, including the filters, to be integrated onto a single integrated circuit.

#Radio receivers, or tuners, are widely-used in applications requiring the reception of electromagnetic energy. Applications can include broadcast receivers such as radio and television, set top boxes for cable television, receivers in local area networks, test and measurement equipment, radar receivers, air traffic control receivers, and microwave communication links among others. Transmission of the electromagnetic energy may be over a transmission line or by electromagnetic radio waves.

#The design of a receiver is one of the most complex design tasks in electrical engineering. In the current state of the art, there are many design criteria that must be considered to produce a working radio receiver. Tradeoffs in the design's performance are often utilized to achieve a given objective. There are a multitude of performance characteristics that must be considered in designing the receiver. However, certain performance characteristics are common to all receivers. Distortion and noise are two such parameters. The process of capturing the signal creates distortion that must be accounted for in the design of the radio receiver. Once a radio signal is captured, the noise surrounding the received signal in the receiver must be considered. Radio signals are often extremely weak and if noise is present in the circuit, the signal, even though satisfactorily received, can be easily lost in this noise floor. The current state of the art in receiver design is often directed to overcoming these receiver limitations in a cost effective manner.

#These and other features and advantages of the present invention will be better understood from the following detailed description read in light of the accompanying drawings, wherein

#FIG. 1 is an illustration of a portion of the over-the-air broadcast spectrum allocations in the United States;

#FIG. 2 is an illustration of the frequency spectrum of harmonic distortion products;

#FIG. 1 is an illustration of a portion of the radio frequency spectrum allocations by the FCC. Transmission over a given media occurs at any one of a given range of frequencies that are suitable for transmission through a medium. A set of frequencies available for transmission over a medium are divided into frequency bands 102. Frequency bands are typically allocations of frequencies for certain types of transmission. For example FM radio broadcasts, FM being a type of modulation, is broadcast on the band of frequencies from 88 MHz to 108 MHz 104. Amplitude modulation (AM), another type of modulation, is allocated the frequency band of 540 kHz to 1,600 kHz 106. The frequency band for a type of transmission is typically subdivided into a number of channels. A channel 112 is a convenient way to refer to a range of frequencies allocated to a single broadcast station. A station broadcasting on a given channel may transmit one or more radio frequency (RF) signals within this band to convey the information of a broadcast. Thus, several frequencies transmitting within a given band may be used to convey information from a transmitter to a broadcast receiver. For example, a television broadcast channel broadcasts its audio signal(s) 108 on a frequency modulated (FM) carrier signal within the given channel. A TV picture (P) 110 is a separate signal broadcast using a type of amplitude modulation (AM) called vestigial side band modulation (VSB), and is transmitted within this channel.

#In FIG. 1 channel allocations for a television broadcast band showing the locations of a picture and a sound carrier frequencies within a channel are shown. Each channel 112 for television has an allocated fixed bandwidth of 6 MHz. The picture 110 and sound 108 carriers are assigned a fixed position relative to each other within the 6 MHz band. This positioning is not a random selection. The picture and sound carriers each require a predetermined range of frequencies, or a bandwidth (BW) to sufficiently transmit the desired information. Thus, a channel width is a fixed 6 MHz, with the picture and sound carrier position fixed within that 6 MHz band, and each carrier is allocated a certain bandwidth to transmit its signal.

#In FIG. 1 it is seen that there are gaps between channels 114, and also between carrier signals 116. It is necessary to leave gaps of unused frequencies between the carriers and between the channels to prevent interference between channels and between carriers within a given channel. This interference primarily arises in the receiver circuit that is used to receive these radio frequency signals, convert them to a usable frequency, and subsequently demodulate them.