LMV822MM datasheet(21/46 Pages) TI1

21 / 46 page

LMV821-N, LMV822-N, LMV822-N-Q1, LMV824-N, LMV824-N-Q1

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SNOS032H – AUGUST 1999 – REVISED APRIL 2014

Typical Applications (continued)

8.2.2 “Simple” Mixer (Amplitude Modulator)

Figure 40. Amplitude Modulator Circuit

8.2.2.1 Design Requirements

The simple mixer can be applied to applications that utilize the Doppler Effect to measure the velocity of an

object. The difference frequency is one of its output frequency components. This difference frequency magnitude

(/FM-FC/) is the key factor for determining an object's velocity per the Doppler Effect. If a signal is transmitted to a

moving object, the reflected frequency will be a different frequency. This difference in transmit and receive

frequency is directly proportional to an object's velocity.

8.2.2.2 Detailed Design Procedure

The mixer of Figure 40 is simple and provides a unique form of amplitude modulation. Vi is the modulation

frequency (FM), while a +3V square-wave at the gate of Q1, induces a carrier frequency (FC). Q1 switches

(toggles) U1 between inverting and non-inverting unity gain configurations. Offsetting a sine wave above ground

at Vi results in the oscilloscope photo of Figure 41.

8.2.2.3 Application Performance Plot

Figure 41. Output signal of Figure 40

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Product Folder Links: LMV821-N LMV822-N LMV822-N-Q1 LMV824-N LMV824-N-Q1

LMV822MM Datasheet(PDF) 21 Page - Texas Instruments