Amplifiers: From Ideal to Real • Why amplify?• Gain = Vout / Vin = sensitivity• Ideal Op Amp• Negative gain summation amplifier• Positive gain for increased Rin• Differential amplifier circuit• Gain-bandwidth product; CMRR• Nonlinear gain: The ideal diode• Instrumentation Amp• Isolation Amplifier

•Horowitz & Hill, The Art of Electronics, Cambridge Univ Press• James K. Roberge, Operational Amplifiers: Theory & Practicecan download at: http://web.mit.edu/klund/www/books/opamps181.pdf• Burr-Brown HANDBOOK OF OPERATIONAL AMPLIFIER APPLICATIONScan download at: http://focus.ti.com/lit/an/sboa092a/sboa092a.pdf

References:

If Rf = 1000*Rs and G is 106, then Vin is in the range of 1mV, a so-called virtual ground.

Summation

Input impedance of NGSA

mechatronics.mech.northwestern.edu/design_ref/electrical_design

• Input resistance = Vin/Iin = R1= Rs ≈ 1KΩ • Way less than the 1012Ω of the op amp itself• NG: R1 may become voltage divider withsensor output resistance• Impedance includes frequency-dependent current-voltage relationship e.g. V(jω)=jωC*I(jω);impedance is a complex number

Unity Gain Voltage Follower

http://ytdp.ee.wits.ac.za/cctpng/Follower.png

A good circuit for isolation

Positive gain single input op amp ckt

If Rs = 0 then Vout = Vin, UGVF

The positive gain amplifier cannot have a gain less than 1.

It can have only one input.

Differential amplifier with external resistors

Current-voltage relationship of a diode

• Where kT/q is about 25mV at room temp

http://keywon.com/wiki/images/http://electricalandelectronics.org

Ideal diode / half wave rectifer

• When VIN > 0 volts output current can flow through the diode and does so until Vin = Vout. (low Rf, like UGVF) • When Vin < 0 the the diode looks like a high resistance, the op amp output saturates at the negative supply voltage, and the left resistor "pulls down" VOUT until it's zero.

Log amplifier

http://www.regentsprep.org/Regents/math/algtrig/ATP8b/exponentialFunction.htm

Absolute value / Full wave rectifier

www.eleinmec.com/

www.physics.udel.edu/~nowak/phys645/More_opamp_circuits.htm

A compression function of input: suppresses large spikes on input

www.corollarytheorems.com/Design/opamp.htm

Exponential (anti-log) amplifier

A non-linear amplifier used to emphasis positive spikes in waveform; makes sense only when Vs > 0.

… getting the signs of Vin and Vout figured out…

Op Amp as integrator

Where we know a capacitor’s current-voltage relationship is (from Laplace transforms)

GBWP and CMRR (LF353)

dB = 20*log10(out/in)

(Implies first order LP filter in op amp)

Instrumentation Amplifier AD524

• No external components needed• pins to select gains of 10, 100, 1000. • GBWP 25MHz• Common mode rejection ratio of 120 dB• Data sheet: www.analog.com/static/imported-files/data_sheets/AD524.pdf• p. 4: differential resistance 109Ω• p. 8: Absolute Maximum Ratingsdimensions in mm• p. 10: CMRR (freq)Gain (freq)• Settling time: 10μsec• p. 18: Ground, analog and digital; ground mecca•www.analog.com/en/other-products/militaryaerospace/ad524/products/product.html#ppa_print_table

Isolation Amplifier AD203

• UGVF • optical isolation; (wireless isolation) • transformer isolation• www.analog.com/en/amplifiers-and-comparators/isolation-amplifiers/ad203/products/product.html•Data sheet: www.analog.com/static/imported-files/data_sheets/AD203SN.pdf • Modulator is a Volt→Freq converter on input, and “tach” on output • single +15v supply• input impedance 1012Ω• low GBWP about 1MHz• CMRR about 120 dB

Iso Amp block diagram

Op amp as example of negative feedback

• When we come later to the topic of automatic control by negative feedback, we will see the op amp as a good example