AMC1305L25-Q1 Datasheet, PDF (22/38 Pages) Texas Instruments – High-Precision, Reinforced Isolated Delta-Sigma Modulators

AMC1305L25-Q1, AMC1305M05-Q1, AMC1305M25-Q1
SBAS797 – FEBRUARY 2017
Feature Description (continued)
0
-20
-40
-60
-80
-100
-120
-140
10
100
1k
10k 100k
1M
10M
Frequency (Hz)
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Figure 49. Quantization Noise Shaping
8.3.3 Digital Output
A differential input signal of 0 V ideally produces a stream of ones and zeros that are high 50% of the time. A
differential input of 250 mV (for the AMC1305x25-Q1) or 50 mV (for the AMC1305M05-Q1) produces a stream of
ones and zeros that are high 90% of the time. A differential input of –250 mV (–50 mV for the AMC1305M05-Q1)
produces a stream of ones and zeros that are high 10% of the time. These input voltages are also the specified
linear ranges of the different AMC1305-Q1 versions with performance as specified in this document. If the input
voltage value exceeds these ranges, the output of the modulator shows non-linear behavior while the
quantization noise increases. The output of the modulator would clip with a stream of only zeros with an input
less than or equal to –312.5 mV (–62.5 mV for the AMC1305M05-Q1) or with a stream of only ones with an input
greater than or equal to 312.5 mV (62.5 mV for the AMC1305M05-Q1). In this case, however, the AMC1305-Q1
generates a single 1 (if the input is at negative full-scale) or 0 every 128 clock cycles to indicate proper device
function (see the Fail-Safe Output section for more details). The input voltage versus the output modulator signal
is shown in Figure 50.
The density of ones in the output bit-stream for any input voltage value (with the exception of a full-scale input
signal as described in Output Behavior in Case of Full-Scale Input ) can be calculated using Equation 1:
V _IN
V _Clipping
2 * V _Clipping
(1)
The AMC1305-Q1 system clock is typically 20 MHz and is provided externally at the CLKIN pin. Data are
synchronously provided at 20 MHz at the DOUT pin. Data change at the CLKIN falling edge. For more details,
see the Switching Characteristics table.
Modulator Output
+FS (Analog Input)
-FS (Analog Input)
Analog Input
Figure 50. Analog Input versus AMC1305-Q1 Modulator Output
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