Radio-frequency circuits are represented here by only a few general examples, because the circuits and design methods that have to be used are fairly specialized, particularly for transmission; the reader who wishes more information on purely RF circuits is referred to the excellent amateur radio publications.

At one time, a reference book would have shown discrete circuits for RF and IF receiver stages, but for conventional analogue radio reception these functions are now invariably carried out by ICs.

The Philips TEA5711 is an IC, now quite old (1992) and established, that integrates all the functions of an AM/FM radio from front end to AM detector and FM stereo output in a 32-pin DIL package.

Figure 7.37 shows a suggested application from the datasheet, using a separate TDA5070 output chip. The TEA5711 chip allows a wide range of supply voltage, from 1.8 V to 12 V, and has a low current consumption of 15 mA on AM and 16 mA on FM.

fig 7.37

The input sensitivity for FM is 2.0 ╬╝V, with high selectivity, and the FM input uses a high impedance MOSFET. The main applications are in portable radios.

The Chorus FS1010 from Frontier Silicon is a 179-pin BGA package that implements the most difficult sections of a DAB digital radio receiver, needing only an external RF stage, audio D to A, flash memory, keypad and display for a complete radio.

The chip incorporates 16 K of ROM, 384 K of RAM, and two 8 K cache memories. It is likely that some day we shall have all of these functions on one chip, but until DAB radios sell in more significant numbers and until gaps in transmitting areas are filled in this is not likely to happen rapidly.  One significant difference from radio as we used to know it is that there is no chance of using discrete components.

Much more specialized devices are used for microwave frequencies, and a specialist in semiconductors for these ranges is Tquint Semiconductors. As example, the Tquint TGC1430G multiplier is intended as a ×3 multiplier with an output in the range of 20–40 GHz using stripline architecture with GaAs semiconductors.

No comments:

Post a Comment