Pop Quiz!



Put away your books and take out a sheet of paper. Each question relates to one of The Signal blogs over the past 15 months. If you have difficulty answering, click on the link to bootstrap knowledge on the topic. Answers are at the end so you can score yourself. Have fun!

1.   A gain of -0.1 (inverting) amplifier…

  • a)      is very likely to oscillate.
  • b)      requires an op amp with special stability criteria.
  • c)       will likely be stable with a unity-gain-stable amplifier.
  • d)      requires a special attenuator at the input to assure stable operation.
  • The Inverting Attenuator, G = -0.1

2.    Using an op amp as a comparator…

  • a)      is okay if you don’t connect for hysteresis.
  • b)      can achieve faster response and reduce power.
  • c)       is necessary if you need push-pull “totem pole” type output drive.
  • d)      may require care to avoid turning on differential input clamps.
  • Op Amps used as Comparators—is it okay?

3.   Power supply bypass capacitor(s)...

  • a)      are not generally required in SPICE simulations
  • b)      are important to get accurate SPICE simulations
  • c)       values can be optimized using SPICE simulations.
  • d)      circuit layout can be determined with SPICE simulations.
  • SPICE Simulations and Power Supply Bypassing

4.   For two equal resistors connected in parallel, the resulting thermal (Johnson) spot noise…

5.   Dual op amps will…

  • a)      likely have well-matched offset voltage.
  • b)      likely have well-matched offset voltage drift.
  • c)       a and b.
  • d)      may save space and cost.
  • Matchy Matchy—how alike are dual op amps?

6.   For unused op amps in a dual or quad package, it’s best to…

  • a)      connect in G=1 with input connected within its C-M range.
  • b)      leave all pins unconnected.
  • c)       connect both inputs to ground and leave output unconnected.
  • d)      !  This is an unwise practice. You should use a single op amp instead.
  • The Unused Op Amp—what to do?

7.   Photodiodes…

  • a)      have a more linear response when forward biased.
  • b)      generate a linear output voltage with incident light power.
  • c)       provide a light dependent current with zero applied voltage.
  • d)      behave as a light-dependent resistor in photoconductive mode.
  • Illuminating Photodiodes ;-) 

8.   The input impedance of a practical transimpedance amplifier (TIA)…

9.   Regarding comparators and hysteresis, …

  • a)      high performance types have low hysteresis.
  • b)      it’s possible to add hysteresis to control “chatter” at transitions.
  • c)       hysteresis creates delay in the transition and should be avoided in high speed circuits.
  • d)      hysteresis occurs in comparators driving inductors that use certain core materials.
  • Comparators—some practical stuff

10.   Potentiometers…

  • a)      should not be used as variable resistors.
  • b)      should be used ratiometrically, when possible.
  • c)       cannot be replaced with electronic components.
  • d)      perform best with a logarithmic taper.
  • When Potentiometers go to Pot

11.   When multiple precision signal processing stages are required…

  • a)      it’s generally best to put substantial gain in the first stage.
  • b)      lower gain in the first stage improves temperature stability and reduces its offset.
  • c)       the last stage is generally the most critical and needs greatest attention.
  • d)      gain should be equally distributed in all stages.
  • Where to Put Your Gain—waxing philosophical

12.   The ESD tolerance of an IC component provided in a data sheet…

  • a)      applies to handling and assembly prior to circuit operation.
  • b)      applies to “typical” circuit operation conditions.
  • c)       is tested on every production IC.
  • d)      is sample tested in production of most ICs.
  • ESD… Zapp!  

13.   Equalizing the effective resistance at the inputs of an op amp…

  • a)      is standard practice and conforms to specified operating conditions.
  • b)      is often unnecessary.
  • c)       reduces offset voltage created by input offset current.
  • d)      improves op amp stability.
  •  Input Bias Current Cancelation Resistors

14.   The output voltage of a thermocouple…

  • a)      is approximately proportional to temperature Kelvin.
  • b)      is generated at the junction of two dissimilar conductors.
  • c)       a)  and  b)
  • d)      is approximately proportional to the temperature difference of the two junctions.
  • Thermocouples—stuff that every analog designer should know

15.   The noise (flat-band) of an amplifier is 5uV measured from 20kHz to 100kHz bandwidth. Its spectral noise density is…

16.   Flicker (or 1/f) noise…

  • a)      ends at the corner frequency.
  • b)      rolls off at approximately 20dB/decade of frequency.
  • c)       rolls off at approximately 10dB/decade of frequency.
  • d)      has equal energy in each 1Hz of bandwidth.
  • 1/f, Flicker Noise—the flickering candle

17.    Decompensated op amps…

  • a)      provide wider gain-bandwidth than similar unity-gain-stable op amps.
  • b)      are generally more stable in G=1.
  • c)       have greater offset voltage drift over temperature.
  • d)      have higher quiescent current.
  • Decompensated Op Amps

18.    Chopper op amps…

  • a)      are generally less stable than standard continuous-time op amps.
  • b)      have nearly flat (constant) spectral density throughout their useful range.
  • c)       should be used when very low input bias current is required.
  • d)      should be used on big, noisy motorcycles.
  • Chopper Op Amps—are they really noisy?

19.    The stripe on one end of a tubular polyester capacitor…

  • a)      should be connected to ground.
  • b)      should be connected to the more negative potential node.
  • c)       should be connected to the lower impedance node.
  • d)      indicates capacitance tolerance.
  • PCB Layout Tricks—striped capacitors and more

20.    For a low noise op amp stage with low source impedance…

Score yourself…

  • 18-20   Bob Pease1 would be so pleased!  (see note below)
  • 16-17   Analog-savvy!
  • 14-15   Analog-capable.
  • 12-13   Possibly a digital designer.
  • 0-11     Are you a software wonk?  :-)

This was just a sampling of 60+ scintillating The Signal topics over the past 15 months. I hope this was fun and comments are welcome, as always.

Bruce       email:  thesignal@list.ti.com

Note:  Launch of this blog coincides with the second anniversary of the death of Bob Pease. He would be so pleased with your interest in analog, no matter what your score!  RIP RAP