1. Field of the Invention
The present invention relates to radio frequency signal tuners, and specifically to configurations with multiple tuners connected to one signal source.
2. Prior Art
It is often desired to have two or more tuners receive different, or occasionally identical, signal channels from the same input source simultaneously. This situation arises, for example, in picture-in-picture applications. Another example is a watch-and-record set-top box where one tuner is used for receiving the channel for the TV whereas the other tuner is receiving a channel that is being recorded. The signal source to the multiple tuners can be taken directly from a coaxial cable connector or alternatively from an amplified or filtered signal inside a set-top box.
In prior art, the radio frequency (RF) input signal is usually distributed to the tuners through a daisy-chain, as shown in FIG. 1. This has benefits when using traditional can tuners. These tuners tend to be physically large and the interconnect between them can have significant physical and electrical length. For this reason, the interconnect is usually done with transmission lines or coaxial cables to avoid reflections and other undesirable loading effects. However, this interconnection requires that the loop-through outputs as well as the RF inputs must be controlled impedances that match to the transmission line characteristic impedance, for example 75 Ohms.
In this type of system, the loop-through output can be derived from the RF input by using an RF splitter. This is highly linear but entails loss in both the tuner input signal as well as the loop-through output. Consequently, the signal-to-noise ratio will be degraded for both. Alternatively, an active splitter using an amplifier can be used, which reduces the signal-to-noise degradation but introduces distortion. The end result is that the signal quality is degraded through each stage of the daisy chain.
U.S. Patent Application Publication, US 2003/0035070 A1 published Feb. 20, 2003 to Fanous, et al, entitled “Method and System for Multiple Tuner Application Using a Low Noise Broadband Distribution Amplifier”, incorporated herein by reference, discloses a system for multiple tuners using an active splitter, which degrades the signal passed to the tuners.
U.S. Patent Application Publication, US 2005/0253663 A1 published Nov. 17, 2005 to Gomez, et al, entitled “Multi-tuner Receivers with Cross Talk Reduction”, incorporated herein by reference, discloses multi-tuner receivers with cross talk reduction that uses an amplifier and alternatively a passive splitter, which degrades the signal passed to the tuners.
U.S. Patent Application Publication, US 2005/0195335 A1 published Sep. 8, 2005 to Gomez, et al, entitled “Multi-input Multi-output Tuner Front Ends”, incorporated herein by reference, discloses a front-end circuit for a multiple tuner television receiver that uses adjustable gain amplifiers and separates the signal into a multi-band signal. A multiplexer and switch directs bands to individual tuners. Each of these circuit elements degrades the signal passed to the tuners.
The aforementioned patent application publications illustrate the prior art approach of using amplifiers or a splitter to distribute the RF signal to multiple tuners.
U.S. Pat. No. 6,897,904 issued May 24, 2005 to Potrebic et al., entitled “Method and apparatus for selecting among multiple tuners”, incorporated herein by reference, discloses a multiple tuner receiver for a broadcast signal. This disclosure concerns the selection among tuners, each receiving a common signal, but does not address how to couple the signal to multiple tuners with minimal signal degradation. The disclosure simply shows two tuners connected to the same source without addressing impedance matching or signal degradation.
The prior art tuner interconnection causes signal quality degradation when multiple tuners receive the same signal, even when the tuners are selecting different channels from the same source.