Rainbow Electronics MAX1011 - Manual (Page 7)

For applications where a DC component of the input
signal is present, Figures 4 and 5 show single-ended
and differential DC-coupled input circuits. The amplifi-
er’s input common-mode voltage range extends from
1.75V to 2.75V. To prevent attenuation of the input
signal’s DC component in this mode, disable the offset-
correction amplifier by grounding the OCC+ and OCC-
pins (Figures 4 and 5).
ADC
The ADC block receives the analog signal from the
input amplifier. The ADC uses flash conversion with 63
fully differential comparators to digitize the analog input
signal into a 6-bit output in offset binary format.
The MAX1011 features a proprietary encoding scheme
that ensures no more than 1LSB dynamic encoding
error. Dynamic encoding errors resulting from meta-
stable states may occur when the analog input voltage,
at the time the sample is taken, falls close to the deci-
sion point for any one of the input comparators. The
resulting output code for typical converters can be
incorrect, including false full- or zero-scale outputs. The
MAX1011’s unique design reduces the magnitude of
this type of error to 1LSB.
Internal Voltage Reference
An internal buffered-bandgap reference is included on
the MAX1011 to drive the ADC’s reference ladder. The
on-chip reference and buffer eliminate any external
(high-impedance) connections to the reference ladder,
minimizing the potential for noise coupling from exter-
nal circuitry while ensuring that the voltage reference,
input amplifier, and reference ladder track well with
variations of temperature and power supplies.
Oscillator Circuit
The MAX1011 includes a differential oscillator, which is
controlled by an external parallel resonant (tank) net-
work as shown in Figure 6. Alternatively, the oscillator
may be overdriven with an external clock source as
shown in Figure 7.
Internal Clock Operation (Tank)
If the tank circuit is used, the resonant inductor should
have a sufficiently high Q and a self-resonant frequen-
cy (SRF) of at least twice the intended oscillator fre-
quency. Coilcraft’s 1008HS-221, with an SRF of
700MHz and a Q of 45, works well for this application.
Generate different clock frequency ranges by adjusting
varactor and tank elements.
An internal clock-driver buffer is included to provide
sharp clock edges to the internal flash comparators.
The buffer ensures that the comparators are simultane-
ously clocked, maximizing the ADC’s effective number
of bits (ENOB) performance.
MAX1011
Low-Power, 90Msps, 6-Bit ADC
_______________________________________________________________________________________ 7
Figure 4. Single-Ended DC-Coupled Input
Figure 5. Differential DC-Coupled Input
MAX1011
INPUT
AMP
20k
2.35V INTERNAL REFERENCE
20k
IN+
OCC+ OCC-
IN-
OFFSET CORRECTION DISABLED
V SOURCE
V CM
1.75V TO 2.75V
OFFSET
CORREC-
TION
MAX1011
INPUT
AMP
20k
2.35V INTERNAL REFERENCE
20k
IN+
OCC+ OCC-
IN-
OFFSET CORRECTION DISABLED
V SOURCE
DIFFERENTIAL SOURCE
WITH COMMON MODE
FROM 1.75V TO 2.75V.
OFFSET
CORREC-
TION