G6B

ICs, connectors and ferrites

Tell analog, digital and microwave ICs apart, pick the right RF connector, and explain how ferrite chokes and toroids work.

11 pool questions1 on the exam

Syllabus: Analog and digital integrated circuits (ICs); microwave ICs (MMICs); display devices; RF connectors; ferrite cores

ICs come in analog, digital and microwave flavours

An integrated circuit packs many parts onto one chip. An op-amp works on smoothly varying signals, so it is analog. Logic chips work on ones and zeros and are digital. A MMIC (Monolithic Microwave Integrated Circuit) is a whole microwave stage on a single chip.

Analog = smooth signals. Digital = ones and zeros. MMIC = microwave stage on one chip.

Of the digital families, CMOS draws much less power than TTL. That is its advantage.

RememberOp-amp = analog. MMIC = Monolithic Microwave IC. CMOS beats TTL on low power.

An LED glows when forward biased

An LED is a diode that emits light. Connect it forward biased (anode toward +) and current flows and it lights. Reverse it and it stays dark.

Forward: the anode is on the + side, so current flows.

RememberLED emitting light = forward biased.

Pick the connector by frequency and job

Each connector has a typical range and use. The higher the frequency, the smaller and more precise the connector must be.

Match the connector to the job: DC and audio, HF and VHF, or microwave.

Type N: moisture-resistant, useful to 10 GHz. It is not a plated PL-259.
BNC: low SWR to about 4 GHz at 50 Ω.
SMA: small threaded connector for signals up to several GHz.
RCA phono: low frequency or DC connections.

Memory hookN for Nasty weather, SMA for Small, RCA for audio and DC.

A ferrite adds impedance to common-mode current

Common-mode current flows along the outside of a coax shield, all in the same direction. The wanted signal inside the cable is equal and opposite, so the ferrite does not affect it. The ferrite just creates an impedance in the path of the common-mode current.

The ferrite adds impedance to common-mode current only. The wanted signal passes untouched.

RememberFerrite choke = impedance in the common-mode path. It blocks, it does not cancel or convert.

Ferrite cores: the mix sets the frequency range

A ferrite's behaviour at different frequencies depends on its composition, or mix, not on its size or shape. Wound as a toroid it gives a large inductance, a mix chosen for your frequency range, and a field that stays mostly in the core. All three are advantages.

Toroid: big inductance from few turns, field kept in the core, and the mix tuned to a frequency range.

RememberMix decides the frequency. Toroid: large inductance, tailored mix, contained field.

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Compendium articles on the ideas in this lesson, beyond what the exam asks.

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Practise the 11 pool questions for this group. Answers are shuffled, and every one comes with a one-line "why".

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