JAJSLQ5C April 2021 – September 2022 ADS127L11
PRODUCTION DATA
The ADC has two programmable input ranges: 1x and 2x, where the 1x range is defined by VIN = ±VREF and the 2x range is defined by VIN = ±2 · VREF. The 2x input range doubles the available range when using a reference voltage = 2.5 V or less. The 2x input range typically improves SNR by +1 dB, but this requires driving the inputs to the 5-V supply rails to achieve full SNR when using a 2.5-V reference voltage. The best available SNR performance (4 dB improvement typical) is by using a 4.096-V or 5-V reference voltage (be sure to program the ADC to the high-reference range mode). The 2x range operation is internally forced to the 1x range mode when the high-reference range is selected. See the CONFIG1 register to program the input range. Table 8-2 summarizes the ADC input range options.
INP_RNG BIT(1) | INPUT RANGE (V) |
---|---|
0 | ±VREF |
1 | ±2·VREF |
In some cases, the full available input range is limited by the power supply voltage. For example, the input range exceeds the power supply voltage when using a 3-V power supply with a 2.5-V reference voltage in the 2x range mode.
The ADC also provides the option of extending the input range beyond standard full-scale range. In this mode, the input range is extended by 25% to provide signal headroom before clipping of the signal occurs. Output data are scaled such that the positive and negative full-scale output codes (7FFFFFh and 800000h) are at ±1.25 · k · VREF, where k is the 1x or 2x input range option.
The SNR performance degrades when the signal exceeds 110% standard full-scale range because of modulator saturation. The modulator MOD_FLAG bit of the STATUS register indicates when modulator saturation occurs. Figure 8-4 shows SNR performance when operating in the extended range. See the CONFIG2 register to program the extended range mode.