Match the following : Codes :List - I List - II (a) A/D Convertor (i) Impedance Matching (b) Emitter Follower (ii) VCO (c) Schmitt Trigger (iii) Successive Approximation (d) Phase Locked Loop (iv) Hysteresis
(a)-(iii), (b)-(i), (c)-(iv), (d)-(ii)
Each item in List-II is the one word that identifies its circuit.
(a) A/D converter → (iii) successive approximation. This is the standard medium-speed conversion technique: a SAR performs a binary search, setting each bit from the MSB down, comparing an internal DAC output with the input at every step. An n-bit conversion takes exactly n clock cycles, independent of the input value.
(b) Emitter follower → (i) impedance matching. The common-collector stage has voltage gain just under unity but a very high input impedance \(\beta(r_{e}+R_{E})\) and a very low output impedance \(r_{e}+R_{S}/\beta\). It therefore takes a signal from a weak, high-impedance source and delivers it to a heavy load without loading the source — the definition of a buffer.
(c) Schmitt trigger → (iv) hysteresis. Positive feedback gives the comparator two different thresholds, an upper trip point for a rising input and a lower one for a falling input:
\(V_{UT},\ V_{LT}=\pm\dfrac{R_{2}}{R_{1}+R_{2}}V_{sat}\)
The gap between them is the hysteresis, and it is what stops a slowly changing or noisy input from producing multiple false transitions at the switching point.
(d) Phase locked loop → (ii) VCO. A PLL is three blocks — a phase detector, a loop filter and a voltage-controlled oscillator — connected in a loop. The phase detector compares input and VCO phases, the filtered error steers the VCO, and the loop settles when the two frequencies are locked.
| Circuit | Signature | Code |
|---|---|---|
| A/D converter | Binary search, n clocks | (iii) |
| Emitter follower | High Zin, low Zout | (i) |
| Schmitt trigger | Two trip points | (iv) |
| Phase locked loop | Contains a VCO | (ii) |
The order (iii), (i), (iv), (ii) is option 2. Note that one certain link is enough here: only option 2 pairs the Schmitt trigger with hysteresis.
Hence, the correct match is (a)-(iii), (b)-(i), (c)-(iv), (d)-(ii).
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