About the IC ZN 415
In the late eighties “Ferranti" introduced this wonderful little chip (IC ZN414) which could receive and process AM radio signals all by itself without involving complex component and tuning networks normally associated with discrete radio circuits. Using this IC it became possible to manufacture very small match box-sized radio sets, which within no time became very popular among school kids and the electronic enthusiasts. Some years later the company further introduced an improved version of this IC in the form of the ZN 415.
Although to many, ICs are just “black boxes," it may be rather interesting to know what really goes on inside, especially when something is so tiny, yet equipped with such outstanding features:
A ZN415 actually consists of an embedded ZN414 inside its package.
The IC ZN414 is basically a ten stage radio tuner and is capable of performing the specified function of receiving and tuning the radio signals only. For amplifying these signals into the headphones, an external amplifier section needs to be employed for enabling the signals to be heard.
In the modified IC ZN415 version, the need for the above external amplifier stage is eliminated by incorporating a built-in two-transistor amplifier stage within the package. This feature enables direct connection of the headphones to the relevant IC pin outs for listening to the received radio signals. Thus making a radio with this IC becomes amazingly simple.
A more elaborate technical discussion is given below:
The frequency range of reception covered by this chip is from 150 kHz to 3 MHz. The range is pretty wide and clearly includes even the long wave bands along with all the MW broadcast bands.
The audio frequency output is around 1 and 1.5 milliwatts into a pair of 64 Ω headphones.
Selectivity is good: 8 kHz bandwidth at -6dB due to the high input sensitivity of the IC, which is typically around 4 MΩ.
An increase of less than 7 dB can be witnessed in the AF output for more than 30 dB RF input, as per the AGC characteristics of the IC.
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