6.3.4 Digital Output

An input signal of 0V ideally produces a stream of ones and zeros that are high 50% of the time. An input of 1V

produces a stream of ones and zeros that is high 90.0% of the time. With 16 bits of resolution, that percentage

ideally corresponds to code 58982. An input of –1V produces a stream of ones and zeros that is high 10.0%

of the time. With 16 bits of resolution, that percentage ideally corresponds to code 6553. These input voltages

are also the specified linear range of the AMC0136. If the input voltage value exceeds this range, the output of

the modulator shows increasing nonlinear behavior as the quantization noise increases. The modulator output

clips with a constant stream of zeros with an input ≤1V or with a constant stream of ones with an input ≥1V. In

this case, however, the AMC0136 generates a single 1 or 0 every 128 clock cycles to indicate proper device

function. A single 1 is generated if the input is at negative full-scale and a 0 is generated if the input is at positive

full-scale. See the Output Behavior in Case of a Full-Scale Input section for more details. Figure 6-3 shows the

input voltage versus the output modulator signal.

Modulator Output

+ FS (Analog Input)

– FS (Analog Input)

Analog Input

Figure 6-3. Modulator Output vs Analog Input

The density of ones in the output bitstream is calculated using Equation 1 for any input voltage VIN. Except for a

full-scale input signal, as described in the Output Behavior in Case of a Full-Scale Input section.

ρ=VIN+VClipping

2×VClipping

(1)

6.3.4.1 Output Behavior in Case of a Full-Scale Input

If a full-scale input signal is applied to the AMC0136, the device generates a single one or zero every 128 bits at

DOUT. Figure 6-4 shows a timing diagram of this process. A single 1 or 0 is generated depending on the actual

polarity of the signal being sensed. A full-scale signal is defined when |VIN| ≥ |VClipping|. In this way, differentiating

between a missing AVDD and a full-scale input signal is possible on the system level.

DOUT

CLKOUT

127 CLKIN cycles

127 CLKIN cycles

VIN

–1.25 V

VIN ≥ 1.25 V

DOUT

Figure 6-4. Full-Scale Output of the AMC0136

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