Analog Electronics

Your reference guide to analog electronics for your electronics projects.

Edited by Lim Siong Boon, last dated 06-Jul-08.

email:    contact->email_siongboon  

website: http://www.siongboon.com


 

Short cut to your reference guides and charts

  1. Op-amp
  2. Capacitor for Signal Filtering
  3. Transistor Switching

 

 

 

 

Op-amp  

Op Amps for Everyone, by Bruce Carter and Ron Mancini from Texas Instruments.

op amps for everyone (Texas Instrument).pdf

op amps for everyone third edition 2009 (Texas Instrument).pdf

op amps for everyone

 

Op-amp application notes from National Semiconductor,

An applications guide for op-amps.pdf

 

Single rail op-amp design from Texas Instruments

single power supply design.pdf

 

Various precision op-amp rectifier design.

http://sound.westhost.com/appnotes/an001.htm


From National Semiconductor and Texas Instruments
op_amp_circuit collection_AN-31.pdf
snla140a, Op Amp Circuit Collection.pdf

Others
op-amp awith offset (bias).pdf
Single Supply Op Amp Design.pdf
CH9 Paul Smith notes.pdf




Type of Op-amp circuit


1) Non-Inverting amplifier
2) Inverting amplifier
3) Unity Buffer amplifier (Voltage follower)
4) Differetial amplifier
5) Suming amplifier
6) Instrumentation ampilfier
7) Oscillator
8) Comparator
9) Threshold detector
10) Zero Level detector
11) Schmitt trigger
12) Integration
13) Differentiation
14) Rectifier
15) Logarithmic output
16) Exponential output

1) Non-Inverting amplifier

Vout = (1+ R2/R1) Vin
- high input impedance
- low output impedance
- higher bandwidth
- minimum gain of 1

A resistor R1||R2 = (R1 x R2) / (R1 + R2) is inserted just before the +ve terminal will keep the input current better balanced.
The added voltage divider has introduced a voltage offset to the output signal Vout.
   

2) Inverting amplifier

Vout = -(Rf/Rin) Vin
- gain can be less than 1

 

When analysing the op-amp as an amplifier (ideal op-amp), the +ve and -ve is to be having the same voltage potential.

A resistor Rin||Rf = (Rin x Rf) / (Rin + Rf) is inserted just before the +ve terminal will keep the input current better balanced.

The added voltage divider has introduced a voltage offset to the output signal Vout.
The voltage divider provides a voltage level which the amplification will be based from. Signal with the same voltage level will not be shift in position, while the rest of the voltage level will be amplified.
   

3) Unity Buffer amplifier (Voltage follower)

Vout = Vin
- high input impedance
- low output impedance

   

4) Differetial amplifier.

- Poor input impedance

Voltage follower added in the front of the input to improve the input impedance. This is also similar to an instrumental op-amp.

Instrumentation amplifier.

 

Op-amp Selection

Brand Part no. Power Supply Spec1 Spec2 Spec3 Comment Price
MAXIM MAX4242 1.8 to 5.5V (single rail) Precision 1
-40 to 85C clean analog signal (best) X
intersil ISL28276 2.4 to 5.0V (single rail) Precision 2
-40 to 125C clean analog signal X
Analog Devices AD8629 2.7 to 5.0V (single rail) Precision 3
-40 to 125C

ok. Can be use for precision analog.(used for Hall sensor project)

X
Analog Devices AD8572 2.7 to 5.0V (single rail) Precision 4
Input Offset 1uV
  -40 to 125C Seems better and cheaper than AD8629 X
Analog Devices AD8602 2.7 to 5.0V (single rail) Precision
Input Offset <0.5mV
  -40 to 125C (used for LED controller project) ok
Analog Devices ADA4665-2ARZ 5 to 16V, 2.5 to 8V

Precision (CMOS)
Input bias current <1pA,
Input offset 1-6mV

  -40 to 125C (used for LED controller project) Fair
intersil ISL28218 3.0 to 40V (single rail) Precision
-40 to 125C --- ---
Texas Instruments OPA2374 2.3 to 5.0V (single rail) Precision
-40 to 125C --- X
Texas Instruments TLC272 4 to 16V (single rail) Precision Output will not reach Vcc 0 to 70 C, -55 to 125C

general use

ok
intersil CA3260 4 to 16V, 2 to 8V Normal
-55 to 125C single/dual supply application X
National Semiconductor LM321, LM324 3 to 32V, 1.5 to 16V wide supply voltage
-40 to 85 C single/dual supply application ok
National Semiconductor

LM158, LM258, LM358, LM2904

3 to 32V, 1.5 to 16V

Normal Output will not reach Vcc 0 to 70 C, -55 to 125C single/dual supply application. Encountered input offset issue. V+ < V- may result in a positive Vout ok
Texas Instruments TLV2402 2.5 to 16V (single rail) Normal
0 to 70 C, -40 to 125C general use X
Microchip Technology MCP6L02 1.8 to 6.0V (single rail)

Normal 1
Input Offset <1~5mV

Near full swing Vout -40 to 125C

general use. Encountered input offset issue. V+ < V- may result in a positive Vout.

ok








Texas Instruments TL061 2V to 15V Normal Output will not reach Vcc -40 to 85 C, -55 to 125C   ok
Texas Instruments TL071 4V to 15V Normal Output will not reach Vcc -40 to 85 C, -55 to 125C   ok
intersil CA741, LM741 5V to 15V Normal Output will not reach Vcc 0 to 70 C, -55 to 125C   ok
Texas Instruments LMV722IDR 2.2 to 5.5V (single rail)
Near full swing Vout -40 to 105 C

On Semiconductor MC33202DR2G 0.9V, 0V to 12V
Near full swing Vout -40 to 105 C, -55 to 125C

National Semiconductor LMP2022MA 2.2 to 5.5V (single rail) Precision
-40 to 125C unable to it make operating
On Semiconductor MC33072 3 to 44V
Output will not reach Vcc -40 to 85C, -40 to 125C

 

(cheap precision op-amp)

Precision usually means a low input offset voltage, which is quite important for voltage comparator, or amplifying small differential input signal.
Input offset <0.5mV will be consider as precision op-amp.
Input offset guide from Analog Device "MT-037, Tutorial Op-amp Input offset voltage.pdf"

   

 

 

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Capacitor for Signal Filtering

 

The following article is a simplied understanding of signal filtering. Basic knowledge of signal filtering is still required before reading this section.

 

 Other references for signal conditioning / filtering
Analog Sensor Conditioning Circuits - An Overview - 00990a.pdf (from Microchip)

The simplest signal low pass filter (LPF) is presented on the right consist of a resistor and capacitor. It is commonly known as RC filter.

This RC layout is applied to circuit with low impedance input, high impedance output. The resistor will be required to complete the filter function. Signal oscillation may occured is the resistor is omitted.

One example would be LPF filtering at the output of the op-amp amplifier circuitry, where filtering is applied to the varying input signal/voltage.

The cutoff frequency of this RC filter
fc = 1/(2πRC)

R will need to be significantly small compare to the load. If the load impedence is high (infinity), then the value of R becomes not very important. If the load impedence is finite, R should be smaller than 1/10 of the load.

Click here for the calculator for the LC filter. frequency and time domain results are on the fly.
- http://sim.okawa-denshi.jp/en/CRtool.php (generate freq/time domain graph on the fly)
- http://www.2pif.com/high-low-pass-filter.php (simple calculator)

RC filter, the simplest low pass filter.

Another way of looking at the same RC filter.

Ideal analysis of the circuit
The signal in the DC or lower frequency signal can be fully transfered to the high impedence (open circuit) output, while the high frequency signal will be absorbed on the resistor (R) components.

What the high frequency signal will see:
AC signal see resistor as a load, capacitor as a short circuit, while inductor as an open circuit. High frequency signal is able to see the capacitor (C) component as a short circuit. The voltage potential of Vout is seen to be the same as the ground reference. This means that the AC signal will be completely absorbed by the resistor R component. High frequency component will not be available at Vout. They are filtered by the RC filter.

What the low frequency signal will see:
DC signal see resistor as a load, capacitor as an open circuit, while inductor as a short circuit. Low frequency signal is unable to see the capacitor (C) component well. The point Vout is seen to have a very high impedance load. This means that the DC signal will be completely transfer to the open circuit output load at Vout. The R component will be seen as small as compare to the open circuit output load. Using the voltage divider concept, most of the low frequency signal will fall on the output Vout. The low frequency signal managed to pass through the RC filter.

Please note that the above explaination is a simplfied analysis of a filter. Ideal analysis helps us to understand the circuit topology (function) at a glance without the need for detail computation. In reality, the open/short circuit represent the degree of attenuation faced by the signal. The degree of signal attenuation is dependant on the frequency of the signal and the capacitor's capacitance.

 

This is another low pass filter consist of only a capacitor. This type of filter will work for current source input. Vin = Vout.

One example would be the capacitors that are found on typical dc power supply filtering at its input or output. Decoupling capacitors (100nF) that are normally found near the power input of an IC is also another example.

 

A capacitor as a low pass filter.
This is a simple high pass filter (HPF) using resistor and capacitor (RC) components. The ideal analysis is similar to the LPF as anaylzed eariler, allow high frequency signal to pass through while low frequency signal are attentuated. RC filter, the simplest high pass filter.

Capacitances required to attenuate or suppress signal of certain frequency. Please note that this formula and the table presented on the right is an approximation for filtering noise from a DC signal.

 

Xc = 1 / (2π f C)

C = 1 / (2π f Xc )

where Xc is the reactance of the capacitor. Xc of 1.0 for the capacitor (open circuit) is possible with lower fequency signal or lower capacitance. To attenuate the AC signal of a particular frequency, Xc has to be low with the correct capacitance implemented.

 

Example:

To attenuate a 50Hz signal by 10 times.

C = 1 / (2π x 50Hz x 1/10) = 31,830uF

This means that to attenuate the 50Hz component by 10 times requires about 33,000uF capacitor connected from the signal to the ground line. This capacitor will filter any frequncy >50Hz on the line.

The table on the right is a simplified guide, which recommend the capacitance to use as a low pass filter for attenuating a particular frequency.

Frequency to Attenuate
Attenuating Factor (Xc)

1/√2
1/2
1/10
1/100
50Hz
2200uF
6800uF
33000uF
330000uF
500Hz
220uF
680uF
3300uF
33000uF
1KHz
113uF
330uF
1600uF
16000uF
10KHz
11uF
33uF
160uF
1600uF
100KHz
1.1uF
3.3uF
16uF
160uF
1MHz
113nF
330nF
1.6uF
16uF
10MHz
11nF
33nF
160nF
1.6uF
100MHz
1.1nF
3.3nF
16nF
160nF
1GHz
113pF
330pF
1.6nF
16nF

 

Max frequency for capacitor (taken from "Op Amps for Everyone")

Capacitor type Max Frequency
Aluminum Electrolytic 100 KHz
Tantalum Electrolytic 1 MHz
Mica 500 MHz
Ceramic 1 Ghz

 

The table on the right summeries the typical capacitor value available commercially. Standard Commercial Capacitor Value:
pF pF pF nF nF nF uF uF uF uF uF
1 10 100 1 10 100 1 10 100 1,000 10,000
1.1 11 110 1.1              
1.2 12 120 1.2              
1.3 13 130 1.3              
1.5 15 150 1.5 15 150 1.5 15 150    
1.6 16 160 1.6              
1.8 18 180 1.8              
2.0 20 200 2.0              
2.2 22 220 2.2 22 220 2.2 22 220 2,200  
2.4 24 240 2.4              
2.7 27 270 2.7              
3.0 30 300 3.0              
3.3 33   3.3 33 330 3.3 33 330 3,300  
3.6 36 360 3.6              
3.9 39 390 3.9              
4.3 43 430 4.3              
4.7 47 470 4.7 47 470 4.7 47 470 4,700  
5.1 51 510 5.1              
5.6 56 560 5.6              
6.2 62 620 6.2              
6.8 68 680 6.8 68 680 6.8 68 680 6,800  
7.5 75 750 7.5              
8.2 82 820 8.2              
9.1 91 910 9.1              
                     
                     
                     

Active filter with op-amp

For flat frequency response, use Butterworth filter

For a sharp cutoff frequency, use Chebyshev filter

For linear phase, use Bessel filter.

 

 

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Transistor Switching  
 

I didn't realised that transistor switching speed can be so important until I had encountered a problem using it for SPI communication. The data communication gets corrupted. Go through all the codes, and eventually found that the transistor switching speed was slow. The current batch of transistor is different from my previous batch; and I always thought that all BC817 npn transistor is the same. I am wrong, it is not. The problem might have been due to my design as well, unable to discharge the base signal in time, to turn off the transistor.

Ch1(yellow) shows the signal input through a 1kohm resistor to the base of the npn transistor. Ch2(blue) is the output at the transitor's collector terminal, with a pull up resistor of 560ohm. The is

The following present the various BC817 transistor's switching digital speed.

Switching speed of my original transistor.

delay of about 0.7us.

using npn BC846

delay of about 2us.

using npn BC817

delay of about 2.5us.

BC817-16LT1G

delay 2us

MMBT4401LT1G

delay 4.5us

MMBTA05LT1G

delay 0.25us

   
Effect of the signal switching without a resistor across the Vbe terminal of a npn transistor BC817.

Effect of the signal switching without a 10kΩ resistor across the Vbe terminal of a npn transistor BC817.

There is a slight improvement in delay, but not very noticable.

Effect of the signal switching without a 10kΩ resistor across the Vbe terminal of a npn transistor BC817.

More than 100% improvement shortening the delay, of the inverted signal by about 1us.

 

 

 

 

email:    contact->email_siongboon  

website: http://www.siongboon.com


 

 

Keyword: op-amp, buffer, inverter, amplifier