ZHCSES1B March 2016 – October 2018 ADS1282-SP
PRODUCTION DATA.
The PGA of the ADS1282-SP is a low-noise, continuous-time, differential-in/differential-out CMOS amplifier. The gain is programmable from 1 to 64, set by register bits, PGA[2:0]. The PGA differentially drives the modulator through 300-Ω internal resistors. A COG capacitor (10 nF typical) must be connected to CAPP and CAPN to filter modulator sampling glitches. The external capacitor also serves as an anti-alias filter. The corner frequency is given in Equation 3:
Referring to Figure 29, amplifiers A1 and A2 are chopped to remove the offset, offset drift, and the 1/f noise. Chopping moves the effects to ƒCLK/128 (8 kHz), which is safely out of the passband. Chopping can be disabled by setting the CHOP register bit = 0. With chopping disabled, the impedance of the PGA increases substantially (>> 1 GΩ). As shown in Figure 30, chopping maintains flat noise density; if chopping is disabled, however, it results in a rising 1/f noise profile.
The PGA has programmable gains from 1 to 64. Table 3 shows the register bit setting for the PGA and resulting full-scale differential range.
The specified output operating range of the PGA is shown in Equation 4:
PGA output levels (signal plus common-mode) should be maintained within these limits for best operation.
PGA[2:0] | GAIN | DIFFERENTIAL INPUT RANGE (V)(1) |
---|---|---|
000 | 1 | ±2.5 |
001 | 2 | ±1.25 |
010 | 4 | ±0.625 |
011 | 8 | ±0.312 |
100 | 16 | ±0.156 |
101 | 32 | ±0.078 |
110 | 64 | ±0.039 |