Operational transconductance amplifier (OTA): The small-signal gain is defined as output current divided by input voltage. In SI units, this transconductance gain is measured in ________.

Introduction / Context:
An operational transconductance amplifier (OTA) is a voltage-controlled current source. Unlike a voltage-output op-amp with V/V gain, an OTA’s fundamental parameter is transconductance, relating input voltage to output current.

Given Data / Assumptions:

• Gain definition: gm = I_out / V_in.
• OTA behaves linearly for small signals about a bias point.
• Units must follow dimensional analysis of current per voltage.

Concept / Approach:
By definition, transconductance is the derivative of output current with respect to input voltage: gm = dI/dV. In SI, current is amperes (A) and voltage is volts (V), so the unit of gm is A/V, known as siemens (S), the same unit used for conductance.

Step-by-Step Solution:

Verification / Alternative check:
Datasheets list gm in micro-siemens to milli-siemens, tunable by bias current, validating the unit selection.

Why Other Options Are Wrong:
Amps: would describe current magnitude, not ratio of current to voltage.

Volts: would describe potential, not a transfer ratio.

No units: incorrect; gm is dimensioned (A/V).

Common Pitfalls:
Confusing OTA gm (A/V) with op-amp voltage gain (V/V). Forgetting that transconductance is tunable via a bias input in many OTA ICs.

Final Answer:
siemens