AMC1204-Q1_15 Datasheet, PDF (18/33 Pages) Texas Instruments – 20 MHz, Second-Order, Isolated Delta-Sigma Modulator for Current-Shunt Measurement

AMC1204-Q1
SLAS886B – JULY 2012 – REVISED JANUARY 2013
www.ti.com
DIGITAL OUTPUT
A differential input signal of 0 V ideally produces a stream of ones and zeros that are high 50% of the time and
low 50% of the time. A differential input of 250 mV produces a stream of ones and zeros that are high 78.1% of
the time. A differential input of –250 mV produces a stream of ones and zeros that are high 21.9% of the time.
This is also the specified linear input range of the modulator with the performance as specified in this data sheet.
The range between 250 mV and 320 mV (absolute values) is the non-linear range of the modulator. The output
of the modulator clips with a stream of only zeros with an input less than or equal to –320 mV or with a stream of
only ones with an input greater than or equal to 320 mV. The input voltage versus the output modulator signal is
shown in Figure 45.
The system clock of the AMC1204-Q1 is typically 20 MHz and is provided externally at the CLKIN pin. The data
are synchronously provided at 20 MHz at the DATA output pin. The data are changing at the falling edge of
CLKIN; for more details see the Timing Information section.
Modulator Output
+FS (Analog Input)
-FS (Analog Input)
Analog Input
Figure 45. Analog Input versus AMC1204-Q1 Modulator Output
FILTER USAGE
The modulator generates a bit stream that is processed by a digital filter to obtain a digital word similar to a
conversion result of a conventional analog-to-digital converter (ADC). A very simple filter, built with minimal effort
and hardware, is a sinc³-type filter, as shown in Equation 1:
3
H(z) =
1 - z^-OSR
1 - z^-1
(1)
This filter provides the best output performance at the lowest hardware size (count of digital gates). For an
oversampling rate (OSR) in the range of 16 to 256, this filter is a good choice. All the characterization in this
document is also done with a sinc³ filter with OSR = 256 and an output word width of 16 bits.
18
Submit Documentation Feedback
Copyright © 2012–2013, Texas Instruments Incorporated
Product Folder Links: AMC1204-Q1