4.6 TRANSRESISTANCE AMPLIFIER AND TRANSCONDUCTANCE AMPLIFIER

A transresistance amplifier converts an input of current to an output of voltage. It is also called a voltage to current converter or V to I converter. It is called transresistance because the efficiency of the amplifier is measured in units of resistance.

The analysis will be done assuming ideal op-amp characteristics. The current entering the op-amp terminals is zero. Accordingly, the current coming from the source will essentially flow through R _f.

Figure 4.10: Transresistance amplifier.

The voltage difference between the two input terminals is zero. Since the voltage at the non-inverting input terminal is zero, the voltage at the inverting input terminal is zero.

? Current through feedback resistance R _f can be calculated.

(4.30)

Therefore, output voltage is proportional to input current.

A transconductance amplifier converts an input of voltage to an output of current. It is also called a current to voltage converter or I to V converter. It is called transconductance because the efficiency of the amplifier is measured in units of conductance.

Transconductance amplifiers are classified into two types. They are transconductance amplifiers with floating load and transconductance amplifiers with grounded load.

Figure 4.11: Transconductance amplifier with floating load.

In the ideal op-amp,

(4.31)

and

(4.32)

Writing Kirchhoff's Current Law at node ' a' yields

(4.33)

Write the equation for current through R ₁:

Substitute equation (4.31) here:

(4.34)

Substitute equation (4.34) in (4.33),

(4.35)

Here the output current...