1. Part I: Amplifier Fundamentals

2. Agenda Ideal Amplifiers Configurations and Operation of Amplifiers
Common Amplifier Source Errors
Understanding Amplifier Specification

3. Why So MANY AMPS??? Lots of Specifications
Some are Important for Different Applications
Each Amplifier is Designed to Improve or Optimize One or a Combination of Specifications
No Ideal Op Amp; YET?
Specialty Amps for a Variety of Applications and Functions
Current Amplifier Trends
Power Consumption - Driven by portable applications
Rail-to-Rail – Higher Dynamic range on lower supply voltage
Smaller Packaging – Circuit density in portable applications
Price – Higher Performance at lower Price

4. What is an “Ideal” Op Amp?
VIN + - G X Y
VOUT
Amplifies a small signal (X) to a larger signal (Y) by Gain of G
Ideal Op Amp Characteristics
Voltage at + Input = Voltage at - Input
Infinite Input Impendence
Zero Output Impendence
Infinite Open Loop Gain
In closed loop Negative Input=Positive Input
Infinite Bandwidth

5. Standard Configurations
VIN + -
Non-Inverting R2 R1
VOUT R2
Inverting
VIN R1 - +
VOUT

6. Operation of an “Ideal” Inverting Amplifier
Virtual Ground Because +VIN = -VIN I2 R2 I1
Vin
Vout - + R1

7. Operation of an “Ideal” Non-Inverting Amplifier
Vin
Vout + - R2 V1 I1 R1

8. Gain-bandwidth product
GBW product = Gain x BandWidth
AOL
100000
GBP=1,000,000
10000
GBP=1,000,000 X
1000
ACL X
100 10 1

9. Nothing is ideal, friends..
- +
REAL
Real Characteristics
Finite open loop gain
Offset voltage
Input bias & offset currents
Finite bandwidth
And, these amplifiers are not free…

10. Input Error Sources - A + Ideal Input Impedance (ZIN) Output Impedance
- +
Ideal
Input Impedance (ZIN)
Output Impedance
(ZOUT) - A +
Input Offset Current (Ios)
Input Bias Current (Ib)
Offset Voltage (Vos)
VOS – The difference in voltage between the inputs [~mV]
IB – The Current into the Inputs [~pA to mA]
IOS – The difference between the + IB and – IB [~IB /10]
ZIN – Input Impedance [MW to GW]
ZOUT – Output Impedance [<1W]

11. Bias Current Drift and Offset Voltage Drift
Offset Voltage is affected by the temperature
Drift is Usually in Units of mV/ ºC
Often a minimum and maximum VOS is Specified over the Temperature Range of the amp
Bias Current is also affected by temperature
Drift is Usually in Units of nA/ ºC
Often a minimum and maximum I BIAS is Specified over the Temperature Range of the amp
FET amplifiers have the lowest input Bias current

12. Very Low Bias Current Fast FETs ™ Amplifier Family Applications+ R2
Low DC Errors
Low Ibias, Vos and Drift
Low Noise
High-Speed
Isc Ib
AD8065
Precision
Photo Diode Pre-Amp
Photodiode Isc is linear over 6-9 decades and is usually in the range of pA-mA
Sensitivity is determined by amount of Isc multiplied by R2
Minimizing Ib will ensure the highest possible sensitivity of the system
Additionally, maximizing the bandwidth minimizes the effects of Ib

13. Noise Gain Noise Gain - gain of error signals (VER) between the inputs
Non-Inverting noise gain = Voltage Gain [R2/R1]
Inverting Noise gain = absolute value of the Voltage Gain +1 I R2 I
Vout - +
VER R1

14. All Input Error Sources End up at the Output
Input Referred Errors are multiplied by the Noise Gain
Initial VOS and VOS Drift Shift VOUT from the expected DC level
VOS drift multiplied by the change in temperature in ºC
Example: 2mV initial offset + 10mV/C with 100C shift and a gain of 5 creates 15mV offset at the output.
IB and IB drift with resistance (R1II R2) at the summing node effectively create an additional VOS
Example: 10mA and R1 = R2 = 2k creates 10mV offset IB R2
IB=10mA
Vout - + R1

15. Input Voltage and Current Noise
CORNER FREQUENCY
FREQUENCY
Voltage or Current Noise Density
2 Sources of Voltage and Current Noise
Low frequency Noise
Magnitude Increases as frequency decreases (1/f)
Wideband noise is flat over frequency
Usually Specified in Noise Density [nV/Hz and pA/Hz]
Multiply by the square root of the frequency range to determine the RMS noise
The intersection is referred to as the corner frequency

16. Common Mode Rejection Ratio (CMRR) & Power Supply Rejection Ratio (PSRR)
CMRR is a ratio (output to input) of amplifier’s ability to reject an equal signal on both of the inputs
Similarly, PSRR is a ratio (output to power supply variation) of amplifier’s ability to reject power supply noise 4V
-4V + -
4mV
-4mV 4V
-4V

17. Rail to Rail Amplifiers
Rail-to-rail amplifiers maximize signal swing, either on the input, the output or both.
True Rail-Rail op amps can swing to within a few mV of their power supply rails.
Non rail-to-rail op amps usually require between 1-3 volts of headroom to the supply rail
Analog Devices Rail to Rail Amplifiers
Rail to Rail Output
Fast FETsTM
AD8091/2 Very Low Cost, High-Performance
Rail To Rail Input
AD8031/2 Low Power High-Speed

18. Rail to Rail vs. Non Rail to Rail Amplifiers
VIN
+VS
Out
-VS In
VOUT In
+VS
R-R
Out
-VS

19. Output Swing Operating Region Decreases with Increased Frequency
Vout
Saturation
Increasing
Frequency
Vout
Operating Region
Iout
Short Circuit
Iout
Operating Region Decreases with Increased Frequency
Output Power [dBm] = 10log[V2rms/(RL)] x1mW

20. Low-Power, Application Considerations
Minimize supply voltage circuitry or battery requirements
Reduce cooling requirements
Lower Heat Dissipation Saves Cost and Space
Smaller heat sinks
Essential in higher density PCB
Increases system stability and reliability
Example:
System with 5 AD8058
(+/-5V)*(6.5mA/amp max)* (10 amps) = 650mW
Using AD8039
(+/-5V)*(1.7mA/amp max)* (10 amps) = 170mW
½ W Power savings

21. Relation Between Open Loop Gain and Phase
Oscillation will occur when Phase Delay 360° and a Gain >0dB
Phase Margin is the phase remaining before oscillation where the gain curve crosses 0dB
Margin of Less than 30 degrees is too little for safe operation
Open Loop Gain vs Freq..
-20
-10 10 20 30 40 50
0.01
0.1 1
100
1000
Frequency (MHz)
AOL (dB)
Degrees
315
180
405
360
270
225
450
Phase margin
Gain
Phase

22. Why Phase Margin is Important
Excessive Peaking in the closed Loop Frequency Response will reduce the phase margin.
In the Time Domain, Low Phase margin causes Ringing
Reducing phase margin further will create sustained ringing or oscillation

23. Slew Rate and Large Signal Bandwidth
Maximum Change in Voltage
Change in Time
Slew Rate Determines the Limit for Large Signal Bandwidth
High Slew Rate
AD8014 + X Y -
Slew Limited

24. Distortion
Changes in the output wave form relative to the input wave form
For pure sign wave in, the output will have some energy at multiples of the input frequency - harmonics 10
-10
-20
-30
-40
-50
-60
-70
-80
-90
-100
-110
-120
[dB] 5 15 20 25 30
Frequency [MHz]
Fundamental
3rd
2nd

25. Ultra Low-Distortion and Noise Applications
Ideal for Buffering ADC Driver
Other Applications
IF/Baseband Amplifiers
Precision Instruments
Baseband and Video Communications
Pin Diode Receivers
Precision Buffer + Rf Rg
AD8007
Passive Filter

26. Various Distortion Specifications
THD – used for Audio and other systems
Total Harmonic Distortion - sum of all distortions at all harmonics
Usually 2nd and 3rd harmonics contribute the most
SFDR - used for communications and other systems
Spurious-Free Dynamic Range in dB
Range between the input signal and largest harmonic

27. NEW High Value, Low Price Products
Fast FETsTM
AD8034 and AD8065
The Highest Bandwidth per Dollar among all FET input Amps 1k (AD8034)
Precision FET (PRA)
Low-Cost High-Performance
AD8091/2
1k (AD8091)
Auto Zero (PRA)
Fast Speed-Low Power
AD8038 and AD8039
Highest Speed per mA at only 1k (AD8038)
CMOS (PRA)
Low Distortion, Low Power
AD8007/8
Best Distortion at specified Is at only 1k (AD8007)

28. Packaging Considerations
All of the Amplifiers are available in small packaging
Maximizes the density of the board
Refer to the datasheet for particular amplifier package
mSOIC
Sewing Needle
SOIC
SC70
SOT23

29. To Be Continued…
Part II: Various Amplifier Configurations