2 Conventional Excitation Amplifier

Conventional excitation amplifiers use discrete linear amplifiers or integrated power operational amplifiers (OPAMPS) such as the ALM2403-Q1 device. Figure 2-1 shows a simplified block diagram of the excitation amplifier.

Figure 2-1 Resolver Excitation Amplifier (Simplified Diagram)

The host system generates the reference signal V_REF­. There are two practical methods to generate this reference signal.

• Using modulated PWM signal
• Using external D/A converter (for example, in the host microcontroller)

The low-pass filter extracts the fundamental frequency and passes the signal to the power stage. The power amplifiers adjust voltage and current levels to match the resolver sensor specification. The output is differential with DC coupling. This eliminates the need for a bipolar power supply. The amplifier must have low offset. Any DC voltage between the outputs generates DC current through the sensor. This current can compromise sensor performance and lifetime.

Figure 2-1, Figure 2-2, and Figure 2-3 show design iterations for the excitation amplifier using the ALM2403-Q1 device. The simple design from Figure 2-1 becomes more complex when there is a need for adjustable over-current protection. Figure 2-3 shows the last iteration with two INA381-Q1 current sense amplifiers. Refer to [1] for more details on how to implement ALM2403-Q1 device in resolver excitation amplifier circuits.

Figure 2-2 Resolver Excitation Amplifier With ALM2403-Q1 (Basic Circuit)

Figure 2-3 Resolver Excitation Amplifier With ALM2403-Q1 (With Output Current Limit)

Figure 2-4 Resolver Excitation Amplifier With ALM2403-Q1 (With Advanced Overcurrent Protection)