Electronics Engineering Magazine

Showing posts with label Analog-Opamps. Show all posts
Showing posts with label Analog-Opamps. Show all posts

Thursday, January 01, 2015

Instrumentation Amp - Op-Amp Designs

This is the best Instrumentation OpAmp, Great CMRR, ensure supply has no ripple and keep analog and digital grounds separate. Ri can be replaced with a trimpot and resistor to alter gain. Connect a preset ends to pins 1 and 8 and preset wiper to VCC for Offset Null when high gains are configured.

Instrumentation Amp - Op-Amp Designs

Instrumentation Amp - Op-Amp Designs

The Input zeners and diodes form a protective clamp for all voltages above VCC-VDD. If supply is changed to +12 -12 change zeners to 12V zeners. Use similar Zeners at output to protect Output from being zapped by over-voltages or high energy - voltage or frequency transients. Add plastic capacitors across Rf for damping AC operation or ripple. Also avoid floating inputs by providing a bias, till you connect it to a sensor; or you will see electrometer like effects.

Three OpAmp Instrumentation Amp xml code

Tuesday, December 09, 2014

Dual Differential Amp - Op-Amp Designs

The Input Impedance of this module is very high and is symmetric. This circuit can be used for strain gauges and for four wire measurements. If inputs are in mV use OP07. The merit is that it uses only 2 OpAmps yet has high differential Input Impedance.

Dual Differential Amp - Op-Amp Designs

Dual Differential Amp - Op-Amp Designs

The Outputs of Opamps are low impedance but still have limits they cannot drive more than a few mA of Current into the Load. If low ohmic value loads are to be applied use external transistors as amplifiers. If inputs Vn-Vp are floating, outputs may be random or oscillating, it is good to have a bias network of 10M resistors to a potential even zero or common, this enables some Vout when input floats.

Dual Differential Amp Tutorial xml code

Monday, December 08, 2014

Differential Amplifier - Op-Amp Designs

A very simple one op-amp diff amp. This amplifies the difference between two inputs Vp and Vn the low impedance of this configuration is a drawback, but can be used in analog computing. Optimum VCC VDD can be +12/-12. AC signals common to Vp and Vn are canceled by this configuration.

Differential Amplifier - Op-Amp Designs

Differential Amplifier - Op-Amp Designs

Use a capacitor like 10nF plastic from pin 2 to 3 or across R2 to make circuit stable. For AC applications use LF351 TLO71 as they have good slew rate and also are FET inputs. For AC applications use a capacitor (1uF) in series with Ri to block DC Components. The Inputs have asymmetrical input impedance this affects CMRR, also use 1% tolerance MFR resistors for Rf and Ri.

Simple Differential Amplifier Tutor xml code

Tuesday, December 02, 2014

Non Inverting Amplifier - Op-Amp Designs

The input impedance of this module is very high, if U1 is OP07 it is in mega/giga ohms, use CA3140 or LF356 fet input opamps to get 1 tera ohm input impedance, but for high gains OP07 is better as it is ultra low offset. This is a good amplifier for sensor outputs, as it is a DC Circuit.

Non Inverting Amplifier - Op-Amp Designs

Non Inverting Amplifier - Op-Amp Designs

The zener diodes protect the opamp inputs, R1 limits current during high voltage inputs and R1 and C1 form a filter to remove some ac components, C1 should be a plastic type as ceramic and electrolytic caps are leaky. A large C1 will slow the response time, the sum of Ri + Rf should be greater than 5k so that output is not loaded. Do not connect output to voltages more than vcc/vdd, it will blow Opamp.

Non-Inverting Op-Amp Tutorial xml code

Tuesday, November 11, 2014

Inverting Amplifier - Op-Amp Designs

This is an Op-Amp Tutorial. Here you see an Operational Amplifier in the Inverting Amp configuration. I have used OP07 as it is almost like an ideal Opamp. The ultra low offset is the best part. Then not really, CA3140 has a Tera Ohm Input resistance but offset not the best. ICL7650 approaches an Ideal Op-Amp and chopper stabilized.

Inverting Amplifier - Op-Amp Designs

These parameters are good for DC Amps. Sensors, Strain Gauge Bridges Signal Conditioning need them. Then when you want a better AC performance, you can use a LF353 with a nice slew rate. Here the DC merits are not of much use.

Inverting Amplifier - Op-Amp Designs

Input Impedance of this module is Ri as pin 2 is at virtual ground, the opamp with feedback tries to maintain pin 2 and 3 at same potential pin 3 is at 0V hence pin 2 is at virtual ground. Clamping diodes protect OpAmp, Rf + Ri is between 5kE and 1ME as an opamp may be able to drive around say 5mA max

Inverting Op-Amp Tutorial xml code

Friday, November 07, 2014

Buffer Unity Gain Amp - Op-Amp Designs

If output impedance of a point is a high value then connecting another circuit at that point will load it, resulting in malfunction or error. Buffers are used as interface between circuits.

Low impedance of an output means it can source/sink lot of current, when you need 2 opamps use LF353 or TL072 which are dual opamps.

Buffer Unity Gain Amp - dapj Tech Widgets

Buffer Unity Gain Amp - Op-Amp Designs

A non-inv FET input is the best buffer, for inverting buffer use high R values. Using very high R values like 2.2M or higher requires a glass epoxy PCB and guard rings around pin 2, 3 to prevent leakage currents on the PCB reaching the PINs.

Also moisture and dust has to be prevented by using RTV coating or Varnish. Use 78L05 and 79L05 for the dual supply required by this circuit.

Buffer Unity Gain Op-Amp Tutorial xml code