10/11/2015Lecture 51 بسم الله الرحمن الرحیم In the name of god

10/11/2015Lecture 52 Electronicmicro. mihanblog.com در این وبلاگ سعی گردیده مطالبی ارایه گردد که برای دانشجویان دوره کاردانی مثمر ثمر بوده و یاور آنان باشد. مطالب جدید نیز در راه است. این فایل به صورت زبان اصلی به دانشجو ارایه میگردد امید است که بهروری لازم را.ببرد

10/11/2015Lecture 53 Contents of this Lecture:  Outlines of signal conditioning circuits design: amplification and filtering  Learn from Examples

Why Need Signal Amplification? 10/11/2015Lecture 54

Outlines of Signal Amplifiers l Designed to amplify input signals to a right level to be noticeable for further uses. l Typical input signals are: thermocouple, RTD, pressure, strain, flow, pH, etc. l Typical outputs include: high level dc voltages (0 to 5 or 0 to 10 volts), process current (0 to 20 mA or 4 to 20 mA) l There are commercial signal conditioners with computer interface ready. 10/11/2015Lecture 55

Operational Amplifier (Op Amp) An operational amplifier (Op Amp) is an integrated circuit of a complete amplifier circuit. A=10 5 typically Op amps have an extremely high gain (A=10 5 typically). R=4 M , typically in order of 100 , typically Op amps also have a high input impedance (R=4 M , typically) and a low output impedance (in order of 100 , typically). 10/11/2015Lecture V i1 V out A B V i2

Characters of Operational Amplifiers   high open loop gain   high input impedance   low output impedance   low input offset voltage   low temperature coefficient of input offset voltage   low input bias current   wide bandwidth   large common mode rejection ratio (CMRR) 10/11/2015Lecture Offset null Not used

Voltage Output from an Amplifier The linear range of an amplifier is finite, and limited by the supply voltage and the characteristics of the amplifier. overdriven If an amplifier is driven beyond the linear range (overdriven), serious errors can result if the gain is treated as a constant. 10/11/2015Lecture 58 A Linearregion Non-linearregion V out V in

Analysis of Op-Amp Circuits The following rules can be applied to almost all op-amp circuits with external feedback: o The current to the input is very small, and may assume that the inputs current is negligible. o It is a reasonable approximation to assume that both inputs are at the same voltage. 10/11/2015Lecture V i1 V out A B V i2

Ideal Amplifiers with or without feedback 10/11/2015Lecture 510 VSVSVSVS V1V1V1V1 V2V2V2V2 VSVSVSVS V1V1V1V1 V2V2V2V2 R1R1 R2R2 VFVFVFVF An ideal op-amp has very high open gain at 0 Hz. Actual amplifier commonly has external feedback.

Inverting Amplifier Point B is grounded, so does point A (very small). Voltage across R 1 is V in, and across R F is V out. The output node voltage determined by Kirchhoff's Current Law (KCL). Circuit voltage gain determined by the ratio of R 1 and R F. 10/11/2015Lecture V in V out R1R1 RFRF A B

Analysis of Inverting Amplifier Ideal transfer characteristics: 10/11/2015Lecture V in V out R1R1 RFRF A B R i+i+i+i+ V+V+V+V+ iFiFiFiF i1i1i1i1 i-i-i-i- V-V-V-V- or

Noninverting Amplifier Op-amp circuit is a voltage divider. 10/11/2015Lecture V in V out R1R1 RFRF A B Circuit voltage gain determined by the ratio of R 1 and R F. Point V A equals to V in.

Differential Amplifier Point B is grounded, so does point A (very small). Voltage across R 1 is V 1, and across R 2 is V 2. Normally: R 1 = R 2, and R F = R 3. Commonly used as a single op- amp instrumentation amplifier. 10/11/2015Lecture 514 RFRF - + V1V1 V out R1R1 A B R3R3 V2V2 R2R2

Design an Instrumentation Amplifier Design a single op-amp instrumentation amplifier. R 1 = R 2, R F = R 3 Determine the instrumentation gain. 10/11/2015Lecture V1V1 V out R1R1 RFRF A B R3R3 V2V2 R2R2

Instrumentation amplifier 10/11/2015Lecture 516 Difference Gain: R6R6 R5R5 R6R V2V2 V1V1 V cm - + V out R1R1 RFRF R3R3 R2R2 VBVB VAVA

Outlines of Filter Design 10/11/2015Lecture 517 Filter inputoutput Filtering: Certain desirable features are retained Other undesirable features are suppressed

Classification of Filters 10/11/2015Lecture 518 Signal Filter Analog FilterDigital Filter Element TypeFrequency Band Active Passive Low-Pass High-Pass Band-Pass Band-Reject All-Pass

Terminology in Filter Design  Signal-To-Noise Ratio (S/N) 10/11/2015Lecture 519  Bandwidth the range of frequencies of |G(j  )|>0.707  Cutoff Frequency the end of pass-band frequency  Break-point of a filter the point with a gain of -3dB

Passive Low-Pass Filter   The pass-band is from 0 to some frequency w p.   Its stop-band extends form some frequency w s, to infinity.   In practical circuit design, engineers often choose amplitude gain of 0.95 for passive RC filters: 10/11/2015Lecture 520  pp ss V out V in C R V out V in RLRL

Passive High-Pass Filter   Its stop-band is form 0 to some frequency  s   The pass-band is from some frequency  p to infinity.   In practical circuit design, engineers choose amplitude gain of 0.95 for passive CR filters: 10/11/2015Lecture 521  ss pp V out V in R C V out V in

Design of Passive Filters 10/11/2015Lecture 522 Transfer Function The amplitude response: The 3dB break-point is at: The amplitude gain: C R V out V in RLRL

Guideline of Pass Filter Design 10/11/2015Lecture 523 R Transfer Function C V out V in RLRL Time Constant Select resistor based on amplitude gain: Select capacitor based on cut-off freq:

Higher Order Filters 10/11/2015Lecture 524 C R V out V in First Order RC Low Pass Second Order RC Low Pass C2C2 V out V in C1C1 R1R1 R2R2 The higher the order of the filter, the closer it approaches ideal characteristics.

Active Filters l Active filters employ Op-Amps to attenuate select frequencies and amplify signal during filtering process. l Q factor of a filter is defined as the ratio of the center frequency f c to the bandwidth f H - f L : 10/11/2015Lecture 525

Design of Low Pass Active Filters Example: Design a low pass filter with cut-off frequency of 5kHz, and DC gain of 10: Two equations, three unknowns 10/11/2015Lecture V in V out R1R1 RFRF A B C2C2 Transfer Function: The -3 dB cut-off frequency: The DC gain:

Design of High Pass Active Filters The -3 dB cut-off frequency: The DC gain: Two equations, three unknowns Select one component based on other conditions, and determine the values of the other two components. 10/11/2015Lecture 527 V out - + V in R1R1 RFRF A B C1C1 Transfer Function:

Filter Class o A filter of a given order can be made to approximate to ideal characteristics in a number of ways, depending on the values of the filter components (or say: depending on the filter class. o Two useful classes are Butterworth (maximally flat) and Chebyshev (equal-ripple) filters (n is the filter order) 10/11/2015Lecture 528 Butterworth FilterChebyshev Filter

Higher Order Active Filters 10/11/2015Lecture 529 V out - + V in R2R2 RbRb C1C1 R1R1 RaRa C2C2 Gain=K Filter Class R1R1 R2R2 C1C1 C2C2 K Buterworth 3.01 dB at  H Chebyshev 1 dB ripple The above list gives the gain and component valves for one of the many choices for  H =1. You may find more combinations from filter design handbook(s).

Learn from Example: Filter Design 10/11/2015 Lecture 5 30 Problem: Problem: Assume a torque sensing device outputs very noisy voltage signal at millivolt range, and the shift being measured is turning at 3,000 rpm. Try to design a signal conditioner for this sensing device. (Assume the input impedance of the signal display device is very large). Electronicmicro. mihanblog.com