AmplifiersAmplifiersAmplifiers An electronic amplifier , amplifier , or amp - is an electronic device that increases the power of a signal . [http:// en .wikipedia .org /wiki /] AAA WheatstoneWheatstoneWheatstone bridgebridgebridge A Wheatstone bridge is an electrical circuit used to measure an unknown electrical resistance by balancing two legs of a bridge circuit . A R1 R3 CD Vcc Vg R2 Rx B Rx is the unknown resistance to be measured . R1, R2 and R3 are resistors of known resistance and the resistance R2 is adjustable . If the ratio of the two resistances R2 / R1 is equal to the ratio of Rx / R3, then the voltage between the two midpoints ; C and D will be zero. AAA WheatstoneWheatstoneWheatstone bridgebridgebridge At the point of balance , the ratio of : R2 = Rx R1 R3 R2 Rx = R3 R1 If all resistor values and the supply voltage (Vcc ) are known , and the resistance of the galvanometer is high , the voltage across the bridge (Vg) can be found by working out the voltage from each potential divider and subtracting one from the other . The equation for this is : Rx R2 Vg = ( − )Vcc R3+ Rx R1+ R2 BBBridgeridgeridge CC Circuitsircuitsircuits Resistive elements are some of the most common sensors . Sensor elements' resistances can range from less than 100 Ω to several hundred kΩ, depending on the sensor design and the physical environment to be measured . Resistance of popular sensors : -Strain Gages (czujniki nap ręż enia ) 120 Ω , 350 Ω , 3500 Ω -Pressure Sensors (czujniki ci śnienia) 350 Ω - 3500 Ω -Relative Humidity (czujniki wigotno ści ) 100k Ω - 10M Ω -Resistance Temperature Devices (czujniki temperatury) 100 Ω , 1000 Ω -Thermistors (termistory) 100 Ω - 10M Ω [www .analog. com ] BBBridgeridgeridge CC Circuitsircuitsircuits The basic Wheatstone bridge [www .analog. com ] BBBridgeridgeridge CC Circuitsircuitsircuits Bridge Circuits In many bridge applications , there may be two , or even four elements which vary . Four commonly used bridges suitable for sensor applications . [www .analog. com ] AmplifiersAmplifiersAmplifiers R R Vcc - Vout K + R R Bridge Amplifier The Differential Amplifier circuit is a very useful op -amp circuit and by adding more resistors in parallel with the input resistors R1 and R3, the resultant circuit can be made to either "Add " or "Subtract " the voltages applied to their respective inputs . One of the most common ways of doing this is to connect a " Resistive Bridge " commonly called a Wheatstone Bridge to the input of the amplifier . [http:// www .electronics -tutorials .ws ] AmplifiersAmplifiersAmplifiers Vcc t Relay Thermistor R1Vcc Rf D - V- K V+ + R3 P R2 Adjust Temperature Activated Switch The circuit acts as a temperature -activated switch which turns the output relay either "ON" or "OFF" as the temperature level detected by the thermistor exceeds or falls below a pre -set value at V+ determined by the position of P. AmplifiersAmplifiersAmplifiers Instrumentation Amplifier Instrumentation Amplifiers (in -amps ) are very high gain differential amplifiers which have a high input impedance and a single ended output . Instrumentation amplifiers are mainly used to amplify very small differential signals from strain gauges , thermocouples or current sensing devices in motor control systems . The instrumentation amplifier also has a very good common mode rejection ratio , CMRR (zero output when V1 = V2) well in excess of 100dB at DC. [http:// www .electronics -tutorials .ws ] AmplifiersAmplifiersAmplifiers V1 + K1 - RB R2 RA Va - R1 K3 R2 RA + Vout Vb - K2 RB + V2 High Input Impedance Instrumentation Amplifier [http:// www .electronics -tutorials .ws ] AmplifiersAmplifiersAmplifiers Instrumentation Amplifier Equation 2R2 RB Vout = (V 2 −V )[1 1+ ]( ) R1 RA AmplifiersAmplifiersAmplifiers Precision Instrumentation Amplifier AD524 FEATURES -Low noise: 0.3 µV p-p at 0.1 Hz to 10 Hz -Low nonlinearity: 0.003% (G = 1) -High CMRR: 120 dB (G = 1000) Low offset voltage: 50 µV -Low offset voltage drift: 0.5 µV/°C -Gain bandwidth product: 25 MHz -Pin programmable gains of 1, 10, 100, 1000 -Input protection, power-on/power-off -No external components required -Internally compensated [www .analog. com ] AmplifiersAmplifiersAmplifiers Functional block diagram [www .analog. com ] AmplifiersAmplifiersAmplifiers Metallization Photograph Contact factory for latest dimensions ; Dimensions shown in inches and (mm) [www .analog. com ] AmplifiersAmplifiersAmplifiers Indirect Ground Returns for Bias Currents —Thermocouple [www .analog. com ] AmplifiersAmplifiersAmplifiers Typical Bridge Application [www .analog. com ] AmplifiersAmplifiersAmplifiers Single Supply Bridge Transducer Amplifier AD22055 FEATURES : APPLICATIONS : -Gain of 400. Alterable from 40 to Interface for Pressure 1000 Transducers, Position, -Supply Voltage: +3 V to +36 V Temperature Transducers -Peak Input Voltage (40 ms): 60 V Indicator, Strain Gages and Other Low Level Signal Sources -Reversed Supply Protection: –34 V -Operating Temperature Range: – 40°C to +125°C [www .analog. com ] Functional block diagram [www .analog. com ] Typical Application Circuit for a Pressure Sensor Interface [www .analog. com ] AmplifiersAmplifiersAmplifiers LT1101 Precision , Micropower , Single Supply Instrumentation Amplifier (Fixed Gain = 10 or 100) APPLICATIONS : FEATURES: a. Differential Signal Amplification in Presence of Common Mode Voltage -Supply Current : 105 µA Max b. Micropower Bridge Transducer -Offset Voltage : 160 µV Max Amplifier -CMRR, G = 100: 100dB Min -CMRR, G = 100: 100dB Min – Thermocouples -Gain Bandwidth Product : -Gain Bandwidth Product : – Strain Gauges 250kHz Min – Thermistors -Single or Dual Supply Operation c. Differential Voltage -to -Current Converter d.4mA to 20mA Bridge Transmitter [www .linear .com ] AmplifiersAmplifiersAmplifiers Block diagram [www .linear .com ] AmplifiersAmplifiersAmplifiers Micropower , Battery Operated Remote Temperature Sensor Trim output to 250mV AT 25 °C, Temperature range = 2.5 °C TO 150 °C, Accuracy = ±0.5 °C [www .linear .com ] AmplifiersAmplifiersAmplifiers Voltage Controlled Current Source [www .linear .com ] AmplifiersAmplifiersAmplifiers Differential Voltage Amplification from a Resistance Bridge [www .linear .com ] AmplifiersAmplifiersAmplifiers INA333 Micro -Power (50mA), Zer ø-Drift , Rail -to -Rail Out Instrumentation Amplifier FEATURES : -Low offset voltage : 25mV (max), -High CMRR: 100dB (min), G ≥ 10 , APPLICATIONS: Supply range : +1.8V to +5.5V , -Bridge amplifiers , Input voltage : (V –) +0.1V to (V+) – -Pressure sensors , 0.1V , -Medical Instrumentation , Output range : (V –) +0.05V to (V+) – -Thermocouple amplifiers , 0.05V , -Data acquisitionn . Operating temperature : –40 °C to +125 °C. [www .ti .com ] AmplifiersAmplifiersAmplifiers Block diagram [www .ti .com ] AmplifiersAmplifiersAmplifiers Basic Connections [www .ti .com ] AmplifiersAmplifiersAmplifiers Single -Supply Bridge Amplifier [www .ti .com ] OscillatorsOscillatorsOscillators An electronic oscillator is an electronic circuit that produces a repetitive , oscillating electronic signal , often a sine wave or a square wave . [http:// en .wikipedia .org /wiki /] OscillatorsOscillatorsOscillators Amplifier Vin+B Vout + A Vin Vout Attenuator B B Vout Vout Basic Oscillator Feedback Circuit OscillatorsOscillatorsOscillators A- open loop voltage gain B- feedback fraction A(Vin + BVout ) = Vout AVin = Vout 1( − AB ) Vout = A Vin 1− AB Oscillator s are circuits that generate a continuous voltage output waveform at a required frequency with the values of the inductors, capacitors or resistors forming a frequency selective LC resonant tank circuit and feedback network . This feedback network is an attenuation network which has a gain of less than one ( B <1 ) and starts oscillations when AB >1 which returns to unity ( A B =1 ) once oscillations commence . OscillatorsOscillatorsOscillators Types of Oscillators Sinusoidal Oscillators - generates a purely sinusoidal waveform which is of constant amplitude and frequency . Non -Sinusoidal Oscillators - generate complex non -sinusoidal waveforms as " Square -wave ", " Triangular -wave " or "Sawtoothed - wave " RCRCRC OscillatorsOscillatorsOscillators The RC Oscillator A single stage amplifier will produce 180 O of phase shift between its output and input signals when connected in a class -A type configuration . In an RC Oscillator circuit the input is shifted 180 O through the amplifier stage and 180o again through a second inverting stage giving us " 180 O + 180 O = 360 O" of phase shift . In a RC Oscillator , we make use of the fact that a phase shift occurs between the input to a RC network and the output from the same network by using RC elements in the feedback branch . RCRCRC OscillatorsOscillatorsOscillators inputC output C C C R R R R o o o 0 o 0 60 180 RC Phase -Shift Network output O 90 Single stage O 60 input output O 180 Three stage Phase shift between the input RC network and the output . RCRCRC OscillatorsOscillatorsOscillators 1 X = C 2πfC = 2 + 2 Z R (X C ) − X φ = tan 1 C R RCRCRC OscillatorsOscillatorsOscillators An amplifier circuit will produce a phase -shift of 180 O between its input and output. If a three -stage RC phase -shift network is connected between this input and output of the amplifier, the total phase shift necessary for regenerative feedback will become 3 x 60O + 180 O = 360 O . o o o C 60 C 120 C 180 AB=1 180 o R R R o 0 RCRC OscillatorsOscillators RC Oscillators Vcc R1 Rl output C 60 o C 120 o C 180 o R R R o Re 0 Basic RC Oscillator Circuit RCRCRC OscillatorsOscillatorsOscillators