Instrumentation Amplifier

referensi

● A Designer's Guide to Instrumentation Amplifier● http://www.analog.com/en/amplifiers-and-

comparators/current-sense-amplifiers/products/design-handbooks/CU_dh_designers_guide_to_instrumentation_amps/resources/fca.html

Sekilas mengenai In-amp

● Not all amplifiers used in instrumentation applications are instrumentation amplifiers

● By no means are all in-amps used only in instrumentation applications

● In-amps are used in many applications, from motor control to data acquisition to automotive

Op-amp VS In-amp

● Sama-sama menguatkan beda tegangan antara input (+) dan (-) nya.

● Mempunyai kemiripan simbol● An instrumentation amplifier is a closed-loop gain

block● An in-amp employs an internal feedback resistor

network that is isolated from its signal input terminals

● gain is either preset internally or is user set (via pins) by an internal or external gain resistor

Step by step in designing in-amp

● Diawali oleh difference amplifier (penguat beda)

Problem pada difference amp

● impedances of the inverting and noninverting inputs are relatively low and unequal● In this example, the input impedance to Vin1 equals 100 kOhm,

while the impedance of Vin2 is twice that, at 200 kOhm● Akibatnya → when voltage is applied to one input while

grounding the other, different currents will flow depending on which input receives the applied voltage. This unbalance in the sources resistances will degrade the circuit’s CMRR

● this circuit requires a very close ratio match between resistor pairs R1/R2 and R3/R4● Sedikit saja perbedaan, akan berakibat buruk pada sistem →

degrade CMRR

Step by step in designing in-amp

● Improving the diff-amp with input buffering

● Kelemahan : setting gain kurang praktis

Step by step in designing in-amp

● A Buffered Subtractor Circuit with Buffer Amplifiers Operating with Gain

● Buffer tidak hanya sebagai voltage follower saja, tetapi juga mempunyai gain

Step by step in designing in-amp

● The Classic 3-Op Amp In-Amp Circuit

2 op-amps in-amp circuit

● Requiring only 2 op-amps, lower power consumption

● Lower CMRR

Apa saja yang menentukan kualitas in-amp

● High AC (and DC) Common-Mode Rejection

● Low Offset Voltage and Offset Voltage Drift

● A Matched, High Input Impedance

● Low input bias and offset current error

● Low noise

● Low nonlinearity

● Simple Gain Selection

● Adequate Bandwidth

● Differential to Single-Ended Conversion

● Rail to rail input output

Monolithic in-amps

● In-amp dalam IC● Produksi analog device

Contoh IC in-amps

● AD8221: High Performance In-Amp → High CMRR, High GBP (Gain Bandwidth Product)

● AD620 : Low cost in-Amp

AD8221 VS AD620

AD8221 VS AD620

Sekilas aplikasi in-amp

● Bridge circuit amplifier

Sekilas aplikasi

● In-line current measurement