6.3.2 Modulator

Figure 6-2 conceptualizes the second-order, switched-capacitor, feed-forward ΔΣ modulator implemented in the

AMC0106M25. The output V5 of the 1-bit, digital-to-analog converter (DAC) is subtracted from the input voltage

VIN = (VINN – VINP). This subtraction provides an analog voltage V1 at the input of the first integrator stage. The

output of the first integrator feeds the input of the second integrator stage. The result is an output voltage V3 that

is summed with the input signal VIN and the output of the first integrator V2. Depending on the polarity of the

resulting voltage V4, the output of the comparator is changed. In this case, the 1-bit DAC responds on the next

clock pulse by changing the associated analog output voltage V5. Thus, causing the integrators to progress in

the opposite direction and forcing the integrator output value to track the average value of the input.

VIN

Integrator 1

V1

V2

V4

V5

V3

fCLKIN

Σ

Integrator 2

Σ

+

–

DAC

0 V

DOUT

Figure 6-2. Block Diagram of a Second-Order Modulator

6.3.3 Isolation Channel Signal Transmission

The AMC0106M25 uses an on-off keying (OOK) modulation scheme to transmit the modulator output bitstream

across the SiO2-based isolation barrier. The transmit driver (TX) illustrated in the Functional Block Diagram

transmits an internally generated, high-frequency carrier across the isolation barrier to represent a digital one.

However, TX does not send a signal to represent a digital zero. The nominal frequency of the carrier used inside

the AMC0106M25 is 480MHz.

Figure 6-3 shows the concept of the on-off keying scheme.

Modulator Bitstream

on High-side

Clock

Signal Across Isolation Barrier

Recovered Sigal

on Low-side

Figure 6-3. OOK-Based Modulation Scheme

AMC0106M25

SBASAX1 – AUGUST 2024

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