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I wanted a functional diagram for the MK 484, kind of like you will see for op amps (http://www.ti.com/lit/ds/symlink/lm741.pdf).

Instead, I only found this: http://www.datasheetcatalog.com/datasheets_pdf/M/K/4/8/MK484.shtml This only has applications, but not how the chip works, nor its functional relationship.

How does it work? What's inside.

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  • \$\begingroup\$ Did you not even open the PDF datasheet provided in your second link? It has the information for that part. \$\endgroup\$
    – DerStrom8
    Nov 5, 2019 at 1:46
  • \$\begingroup\$ The data sheet only has an application circuit \$\endgroup\$
    – ions me
    Nov 5, 2019 at 19:07

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The MK484 is a copy of the Ferranti ZN414. The ZN414 datasheet only shows a block diagram of the internals, but gives some idea of how it works.

It has several stages of rf amplification, AC coupled via small capacitors. The combination of small coupling capacitors and transistor cutoff frequency results in a relatively narrow bandwidth that covers the Long Wave, 455kHz IF, and AM broadcast bands.

These are followed by a transistor acting as an AM demodulator or 'detector'. Output current increases with higher signal strength, which increases voltage across the load resistor and reduces output voltage. This reduces bias current to the input stage which reduces its gain, providing some AGC (Automatic Gain Control) action.

The whole IC only has 10 transistors in it, so each stage may only consist of 1-3 transistors.

enter image description here

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  • \$\begingroup\$ How do the amplifiers get power? I'm trying to see how they can get away without having a v supply on the chip. \$\endgroup\$
    – ions me
    Nov 5, 2019 at 19:05
  • \$\begingroup\$ They get power through the load resistor. Seems crazy, but the 0.1uF capacitor keeps the voltage smooth at rf frequencies, and the lower voltage at higher signal strength probably provides some AGC action. However If the signal is very strong it gets distorted (this is not a Hi-Fi receiver!) \$\endgroup\$ Nov 5, 2019 at 19:12

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