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I see these two terms are used in same context. But what is the difference in meaning? Is difference amplifier a subset of differential ampfier with unity gain? I couldnt find a duplicate question.

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    \$\begingroup\$ Can you show us a context? \$\endgroup\$ – G36 Apr 16 at 16:05
  • \$\begingroup\$ They have exactly the same topology \$\endgroup\$ – Genzo Apr 16 at 16:08
  • \$\begingroup\$ in my experience, the terms are inter-changeable. Tho on silicon, the term diff-pair refers to that first set of transistors; originally just 2 matched devices, then thermal-transient-cancellation and miller-cascading and bias-current cancellation have arrived to greatly complicate that simple 2-device differential-pair schematic. \$\endgroup\$ – analogsystemsrf Apr 16 at 16:33
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There is " no difference " between the terms "Difference Amplifier" and "Differential Amplifier" (pun intended)

They both amplify the difference between 2 nodes, whether you have a signal on both or just one and connect the other one to some DC reference voltage.

Then the impedance ratio is 50% going into the non-inverting side with a gain of 1/2*2=1, it is unity gain while the inverting side has the same divider ratio with a gain of -1 then it is a "unity-gain differential (or difference) amplifier" which is a special case of any "diff amp".( slang description = diffy)

Other info;

The gain and frequency shape can be varied as long as the ratios are matched. So instead of simply Rf/Rin=gain it can be any combination of RLC parts matched on both sides.

Matching is the hard part for discrete parts (0.1% error on 4 parts < 55 dB CMRR while integrated INstrument Amps (INA) offer CMRR > 110 dB needing only 1 R shared to control gain instead of matching 4 parts or 2 ratios, using laser trimmed internal R's.

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