6.3.2 Modulator

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

AMC0136. The output V5 of the 1-bit, digital-to-analog converter (DAC) is subtracted from the input voltage VIN

= (V INP – V SNSN ). 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 or the second integration is

an output voltage V3 that is summed with the input signal VIN and the output of the first integrator V2. Depending

on the value 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

VREF

DOUT

–

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

6.3.3 Isolation Channel Signal Transmission

The AMC0136 uses an on-off keying (OOK) modulation scheme, as shown in Figure 6-3, to transmit the

modulator output bitstream across the SiO2-based isolation barrier. The transmit driver (TX) as 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 AMC0136 is 480MHz.

The AMC0136 transmission channel is optimized to achieve the highest level of common-mode transient

immunity (CMTI) and the lowest level of radiated emissions. The high-frequency carrier and RX/TX buffer

switching cause these emissions.

Modulator Bitstream

on High-side

Internal Clock

Signal Across Isolation Barrier

Recovered Sigal

on Low-side

Figure 6-3. OOK-Based Modulation Scheme

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AMC0136

SBASAZ0A – AUGUST 2024 – REVISED DECEMBER 2024

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