Phase Locked Loops (PLLs), Voltage Controlled Oscillators (VCOs), Mixers

Question 1

What frequency synthesizer circuit uses a phase comparator, look-up table, digital-to-analog converter, and a low-pass antialias filter?

Answer 1

A direct digital synthesizer.

Question 2

A circuit that compares the output of a voltage-controlled oscillator (VCO) to a frequency standard and produces an error voltage that is then used to adjust the capacitance of a varactor diode used to control frequency in that same
VCO is called what?

Answer 2

Phase-locked loop.

Question 3

R input to a mixer is 200 MHz and the local oscillator frequency is 150 MHz. What output would you expect to see at the IF output prior to any filtering?

Answer 3

50, 150, 200 and 350 MHz.

Question 4

What spectral impurity components might be generated by a phase-locked-loop synthesizer?

Answer 4

Broadband noise.

Question 5

In a direct digital synthesizer, what are the unwanted components on its output?

Answer 5

Spurs at discrete frequencies.

Question 6

What is the definition of a phase-locked loop (PLL) circuit?

Answer 6

A servo loop consisting of a phase detector, a low-pass filter and voltage-controlled oscillator.