Your Answer : (Not Answered)

Correct Answer : B

The half-LSB offset is added to reduce the maximum quantization error.

Without the offset, a successive approximation converter truncates: every input between two code levels is rounded down, so the error ranges from 0 to almost 1 LSB. Shifting the D/A comparison levels by half an LSB makes the converter round to the nearest level instead, so the error lies between -1/2 and +1/2 LSB and its maximum magnitude halves.

The offset does not change the number of comparisons, so it does not affect speed; it does not add output bits; and it does not widen the input range, since the full-scale code is unchanged.

Your Answer : (Not Answered)

Correct Answer : C

A Schmitt trigger is a positive feedback op-amp circuit.

Part of the output is fed back to the non-inverting input, so once the input crosses a threshold the output is driven hard to the opposite saturation level. The feedback shifts the threshold, giving two switching levels (upper and lower trip points) and hysteresis, which makes the circuit immune to noise on slowly varying inputs.

An open loop comparator switches at a single threshold and chatters with noise. Negative feedback produces linear amplifiers, not switching circuits. 'Differential input' describes every op-amp and does not distinguish the configuration.

Your Answer : (Not Answered)

Correct Answer : A

The phase error must stay between 0 and π.

In a phase locked loop, the phase detector converts the phase difference between the VCO output and the incoming signal into a control voltage. For the common XOR-type detector, the average output rises linearly as the phase error goes from 0 to \(\pi\) and then falls again from \(\pi\) to \(2\pi\). The loop can correct the VCO only while the error stays on the rising part, 0 to \(\pi\), with the locked operating point normally near \(\pi/2\).

Outside that range the slope reverses, so the feedback has the wrong sign and lock is lost. The ranges 0 to \(\pi/2\), 0 to \(2\pi\) and \(\pi\) to \(2\pi\) are not the monotonic range of that characteristic.

Your Answer : (Not Answered)

Correct Answer : B

The output can be increased by increasing ground pin voltage.

A fixed regulator such as the 78xx holds a fixed voltage between its output and its ground (common) pin. If the ground pin is lifted above circuit ground by a resistor, a Zener diode or a potential divider, the output rises by the same amount: V_out = V_reg + V_{ground pin}.

An external pass transistor increases the current the regulator can deliver, not its voltage. Cascading two regulators only drops the voltage further, and a voltage doubler at the input raises the input, which the regulator then removes, so the output stays fixed.

Your Answer : (Not Answered)

Correct Answer : D

The LM723 is suited to regulation from 2 to 37 V.

The LM723 is a general-purpose adjustable regulator. Its data sheet specifies an output voltage adjustable from 2 V to 37 V, with input voltages from 9.5 V up to 40 V, and an output current of up to 150 mA without an external pass transistor.

The option '9.5 to 40 V' is the input voltage range, not the regulated output. '0 to 40 V' and '0 to 27 V' are wrong because the 723 cannot regulate down to zero; its lowest output is about 2 V.

Your Answer : (Not Answered)

Correct Answer : C

The current sense resistor is placed in series with the emitter of the pass transistor.

In a series regulator, the whole load current flows through the pass transistor and out of its emitter to the load. A small resistor in that path develops a voltage proportional to the load current. When this voltage reaches about 0.6 to 0.7 V, it turns on a current-limit transistor that diverts base drive from the pass transistor, limiting the output current and protecting the circuit from overload or short circuit.

A resistor across the pass transistor or in parallel with the load would not carry the load current, and the collector side is the unregulated input, so the standard current-limiting arrangement senses at the emitter.

Your Answer : (Not Answered)

Correct Answer : A

The cut-off frequency is 1.273 kHz.

For a first order RC low pass filter, active or passive, the cut-off frequency is

\[ \begin{aligned} f_{c} &= \frac{1}{2\pi RC} \\ &= \frac{1}{2\pi (2.5 \times 10^{3})(0.05 \times 10^{-6})} \\ &= \frac{1}{2\pi \times 1.25 \times 10^{-4}} \\ &\approx 1273\ \text{Hz} = 1.273\ \text{kHz} \end{aligned} \]

The other options are the same digits with the decimal point moved, the result of a slip with the powers of ten for kilo-ohms and microfarads: 12.73 kHz and 127.3 kHz are ten and a hundred times too high, and 127.3 Hz ten times too low.