ZSSC3016 datasheet(13/45 Pages) IDT

13 / 45 page

ZSSC3016 Datasheet

January 25, 2016

3) One of the two following cases is valid.

a. If RatioOffset – A2D_offset

≤ 0 then calculate theoretical optimum gain:

Gainopt =(1 – A2D_offset) · Vref / Vmax

b. If RatioOffset – A2D_offset > 0 then calculate

theoretical optimum gain:

Gainopt = A2D_offset · Vref / |Vmin|

with:

Vref = Vrefp – Vrefn = 0.94·VDDB,min ~ 1.5V

4) Select the setup gain (Gainsetup) as the nearest gain to Gainopt, where Gainsetup

≤ Gain

opt.

2.3.2.

Analog-to-Digital Converter

A second-order charge-balancing analog-to-digital converter (ADC) is used to convert the amplifier signal. To

allow optimizing the trade-off between conversion time and resolution, the conversion is split into a MSB coarse

conversion and an LSB fine conversion. The MSB-LSB segmentation is programmable via the Msb and Lsb

settings in the BM_config register stored in the MTP memory (see section 2.4.2). The final ADC resolution is

determined by MSB+LSB-1. The conversion time is proportional to 2

MSB +2LSB. During the MSB coarse

conversion, the ADC input signal is sampled and integrated 2

MSB times, resulting in inherit low-pass behavior and

noise suppression. Possible settings are listed in Table 2.4.

Table 2.4

MSB/LSB Settings

Msb Setup Bits

in BM_config

Number of MSB Coarse

Conversion Bits

Lsb Setup Bits

in BM_config

Number of LSB Fine

Conversion Bits

00BIN

01BIN

10BIN

11BIN

Useful MSB/LSB setups are with LSB = 0 (MSB-only conversions) or combinations of MSB > LSB with

MSB + LSB

≤ 17. Resolutions beyond 16-bit mainly digitize the collected front-end noise and typically do not

improve the system performance. MSB/LSB segmentations with LSB > MSB are also not useful because typically

the resolution remains the same as with the inverse MSB/LSB segmentation, but the noise performance becomes

significantly worse yet the required conversion time stays the same. The ADC conversion times for different

MSB/LSB settings are listed in Table 2.5.

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