LM321

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SNOS935C – FEBRUARY 2001 – REVISED DECEMBER 2014

Typical Applications (continued)

8.2.2 DC Summing Amplifier (VIN's ≥ 0 VDC and VO ≥ VDC)

The summing amplifier, a special case of the inverting amplifier, is shown in Figure 7. The circuit gives an

inverted output which is equal to the weighted algebraic sum of all four inputs. The gain of any input of this circuit

is equal to the ratio of the appropriate input resistor to the feedback resistor. The advantage of this circuit is that

there is no interaction between inputs and operations such as summing and weighted averaging are

implemented very easily.

Where: V0 = V1 + V2 - V3 - V4, (V1 + V2) ≥ (V3 + V4) to keep VO > 0 VDC

Figure 9. DC Summing Amplifier Schematic

(VIN's ≥ 0 VDC and VO ≥ VDC)

8.2.3 Amplitude Modulator Circuit

The modulator circuit is shown in Figure 10. PWM signal is used to switch the MOSFET. When the MOSFET is

on, the circuit acts as an inverting amplifier with gain 1. When The MOSFET is off, the inverting and non-inverting

signals cancel each other out. Therefore, the output switches from –VIN to GND at the carrier frequency.

Figure 10. Amplitude Modulator Circuit Schematic

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