WM2331 Datasheet, PDF (10/25 Pages) Wolfson Microelectronics plc – 10-bit 30MSPS ADC with PGA and Clamp

WM2331
Production Data
PROGRAMMABLE-GAIN AMPLIFIER
VP is amplified by the PGA and fed into the ADC as a differential voltage VQ = VQ+ - VQ-
V_Q = Gain ×V_P = Gain × (V_IN −V_M )
The PGA gain defaults to 1.0 at power-up, but can be programmed from 0.5 to 4.0 in steps of 0.5.
ANALOGUE-TO-DIGITAL CONVERTER
Regardless of the reference configuration, VQ is digitised against ADC Reference Voltages REFTF
and REFBF, full scale values of VQ being given by:
V_{QFS +}
=
REFTF
−
2
REFBF
and
V_{QFS −}
=
−

REFTF
−
2
REFBF


Attempts to convert VQ voltages outside the range of VQFS- to VQFS+ are signalled to the application
by driving the OVR output pin high. If VQ is less than VQFS-, the ADC output code is 0. If VQ is greater
than VQFS+, the output code is 1023.
SIGNAL CHAIN SUMMARY
Combining the above equations and referring back to the input, the positive and negative full-scale
voltages at the AIN pin are:
V_{INFS +}
= V_M
+
REFTF − REFBF
2 × Gain
and
V_{INFS −}
= V_M
−
REFTF − REFBF
2 × Gain
Therefore the input signal span is given by:
V_{INFS +}
− V_{INFS −}
=
REFTF − REFBF
Gain
In order to match the ADC input range to the input signal amplitude, REFTF and REFBF should be
set such that:
REFTF − REFBF = (V_{INFS +} − V_{INFS −} ) × Gain
ADC REFERENCE MODES
The WM2331 supports three basic modes of reference generation, selected by the voltage applied to
the MODE pin. These are summarised and explained in Table 1.
In differential, Centre Span and Top/Bottom modes, the internally generated ADC references are
intened solely for WM2331 internal use and REFTF and REFBF must not be used as voltage
references for any other device in the application.
WOLFSON MICROELECTRONICS LTD
PD Rev 1.4 April 2001
10