Electronic Design

Dual RF Tuner Brings Flexibility To Satellite Set-Top Boxes

Satellite TV installations use a set-top box (STB) that works with a remote low-noise block (LNB) converter at the antenna so the Ku band signals (10.95 to 14.5 GHz) are downconverted to the 950- to 2150-MHz range, making them more friendly to the coax connection between the LNB and STB. But this creates compromises in multi-set installations, as extra wiring is often needed. Any other special arrangement typically results in a more complex and expensive installation.

The TDA20136 dual tuner from NXP Semiconductors solves the problem (see the figure). It integrates a dual eightphase shift keying (8PSK) satellite tuner with some highly desirable pre-tuner circuitry to create a platform that is more flexible in diverse installation scenarios without any hardware changes. This will dramatically reduce design cost and complexity.

The pre-tuner circuitry provides the flexibility that allows set-top boxes to use either a single cable input, splitting the signal internally to the device, or legacy mode with two separated inputs. In both cases, an optional dual loop-through function is available.

The single-input setting is most commonly used when the set-top box is used with a single-cable reception outdoor unit (ODU). In this case, signals from multiple LNBs are multiplexed onto a single cable at the ODU. This single cable can then provide the required signals for many STBs in a single home or multidwelling unit (MDU). With no hardware changes, an STB using this IC can also be used in an installation with a legacy multi-LNB, multi-cable ODU. In this legacy installation, each tuner gets its signal from a separate cable.

“The industry trend towards singlecable reception (SCR) has the potential to dramatically reduce installation costs because there are fewer cables to install, but implementing SCR circuitry in a settop box using a standard satellite tuner is complex and expensive,” said Tim Kirstein of NXP Semiconductors. “We have created the TDA20136 with the highest levels of RF integration to directly address these problems, while also providing the settop box maker with the flexibility to be backwards-compatible with traditional multi-LNB, multi-cable ODUs.”

The TDA20136 system is based on the company’s proven dual-tuner technology with its CX24132. This unique secondgeneration complete dual 8PSK tuner offers outstanding performance and low power consumption. It includes all of the necessary low-noise amplifiers (LNAs), voltage-controlled oscillators (VCOs), synthesizers, mixers, and filters for common applications. Additionally, its small size (7 by 7 mm) enables system designers to reduce the size of front ends. Production will begin this month.



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