Black Box Electronics

1
Black Box Electronics An Introduction to Applied
Electronics in Experimental Physics 2. Analog
BJTs to Opamps University of Toronto Quantum
Optics Group Alan Stummer, www.physics.utoronto.c
a/astummer
2
Active BJTs
Class A with four resistors
Class A with negative feedback
3
MOSFETs(Metal Oxide Semiconductor Field Effect
Transistor)

• Drain to source resistance and/or current 1 /
  gate to source voltage.
• Zero gate current!
• Operate in active region (analog), or saturation
  or cutoff (digital).

• Most common are N-channel for analog, both for
  digital.
• Limited in current ID, voltage VDS and power PD.
• Very very good saturation, RDS(on).
• Limited frequency range, capacitance dominates
  at high frequency.
• Select for current, voltage, speed and RDS(on)
  if saturating.
• Typical voltage VDS range 10V to 200V, extreme
  to 1.5KV.
• Typical current ID range 100mA to 10A, extreme
  to 100A.

4
Sample FET Transfer Curves
A general purpose 48A, 60V N-FET from Fairchild
(Digikey.ca). http//www.fairchildsemi.com/ds/ND/N
DP6060L.pdf
5
NDP6060L Data Sheet Parametric Section
6
Basic Q Switching
7
Sample Linear FET Circuit
Opamp uses a N-FET to increase current driving
capacity. The opamp can supply only tens of mA
but the laser needs ten times more.

• The opamp can drive the Q1 FET from cutoff
  through to saturation.
• All of the laser current goes through R2.
• The opamp monitors the R2 voltage.
• The opamp adjusts the FET gate voltage to control
  the FET conductance and therefore the laser
  current.

8
Less Common Active Parts
IGBT (Insulated Gate Bipolar Transistor)

• Current allowed through collector to emitter is
  proportional to voltage between gate and emitter.
• Voltage controlled like a FET, switches like a
  BJT.
• Used for power control such as motors.
• Pros High voltage and current. Cons slow,
  poor saturation.

Thyristers SCR (Silicon Controlled Rectifier)
Triac

• Anode/MT1 connects to cathode/MT2 once gate
  current exceeds threshold, stays on until
  anode/MT1 current drops below threshold.
• SCR is unipolar, Triac is bipolar.
• Used for motor and lighting controls (F
  control).
• Pros High voltage and current. Cons slow,
  poor saturation.

9
OpAmps(Operational Amplifiers)
_

• Three terminal linear device 2 inputs 1
  output (plus 2 power).
• Hard Rule The output goes positive if the
  input is positive (where input is defined as ve
  input relative to ve input).

• Soft Rule The inputs and output can only range
  between the rails (the positive and negative
  supply pins).

All else is imperfections
10
Basic Stable OpAmp
Almost all opamp circuits are a variation on
this. Understand why this is stable and the rest
is easy.
11
Sample Difference Amp
Output is difference between the inputs. Taken
from Analog Devices AD8605 data sheets, a very
good device series.
12
Sample Instrumentation Amp
Hi-Z (impedance) inputs, difference out, very
fast. Taken from Analog Devices AD8065-6 data
sheets.
13
Sample TIA
Current in, voltage out, used for
photodiodes. Taken from Analog Devices AD8605
data sheets.
14
Sample Filter
Active low pass filter of Sallen-Key
design. Taken from Texas Instruments OPA2735
data sheets.
15
Some OpAmp Errors
16
Basic OpAmp Amplifiers

• f-3dB 1 / 2p R1 C1
• In this example
• Av -100K / 10K -10
• f-3dB 1 / 2p 100K 1nF 1.59KHz
• 0V lt Vout lt 5V
• Vin range depends on Vref

17
? The End ?

• Next 3. Digital Electronics
• 4. Sample Circuits
• 5. Simulations Spice is your Friend
• 6. Eagle hands on If you can, bring a laptop
  with Eagle loaded and the sample schematic and
  board.
• Then More in depth on anything? Suggestions?