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Addressing traditional radio design issues

Posted: 10 Oct 2011     Print Version  Bookmark and Share

Keywords:Radio  tuning wheel  frequency display 

Radio technology has been in existence for more than a century, and traditional wheel-tuned radio products have been used for decades by countless listeners around the world. They have a simple user interface based on a tuning wheel to dial the frequency and a moving needle with a frequency mark to show the tuned station. During the past decade, high-performance DSP-based radio designs have enabled sophisticated new user interfaces with buttons for auto seek/tune capabilities and liquid crystal displays (LCDs) that display the frequency.

As a growing number of portable applications such as mobile phones and portable media players integrate the FM radio function, there's a misconception in the market that traditional radios are no longer needed. The reality is, wheel-tuned radios have remained immensely popular for a number of reasons. For instance, it can be technically challenging to integrate the AM and shortwave (SW) radio feature in portable multimedia devices due to interference and size constraints. Many consumers still prefer to listen to sports news and other audio broadcast content through AM and SW radios such as boom boxes, smart phone docking stations and other portable radio products. Traditionally, these radio products have adopted the appearance of a tuning wheel and a needle with frequency marking to show the tuned frequency.

 traditional radio

Figure 1: Here's a typical wheel-tuned, digital-display radio.

In recent years, DSP-based radios have attracted consumer interest by offering convenient LCD/LED frequency displays and pushbuttons designed to auto-seek the frequency. However, while many radio users appreciate the convenience of displaying frequencies on an LCD or LED panel, they still prefer to use the intuitive tuning wheel (figure 1). For simplification, let's call this market the "wheel-tuned, digital-display" radio, also known as the "analogue-tuned, digital-display" (ATDD) market. (Note that the "analogue" designation is no longer accurate since digital radio ICs predominate in this market; however, we still use the popular industry acronym, ATDD.)

 analogue receiver IC

Figure 2: Simplified system schematic using a traditional analogue receiver IC.

There are multiple ways to design an ATDD radio. Let's consider each design approach from a system level including RF performance, level of complexity, feature differentiation and finally bill of materials (BOM). We'll start by examining the traditional approach of using analogue ICs to design an ATDD radio, then look at creative designs such as "click-wheel" radios using DSP-based radio ICs, and conclude with an overview of new multi-band radio IC technology optimised for the ATTD market.

Analogue IC for ATDD radios
Traditional analogue radio ICs can be used in wheel-tuned digital-display radio designs. However, due to the limitation of the AM/FM receiver's analogue architecture, the receiver IC requires a large BOM because much of the signal processing is performed off chip by other components. In addition, the analogue IC does not provide the tuned frequency information for the display driver. Thus, in these traditional radio solutions, an intermediate-frequency (IF) counter IC is needed to interpret the local oscillator pulses as tuned frequency and translate these pulses to a display driver, which then displays the calculated tuned frequency (figure 2).

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