Rainbow Electronics MAX1011 - Manual (Page 8)

MAX1011
External Clock Operation
To accommodate designs that use an external clock,
the MAX1011’s internal oscillator can be overdriven by
an external clock source (Figure 7). The external clock
source should be a sinusoid to minimize clock phase
noise and jitter, which can degrade the ADC’s ENOB
performance. AC couple the clock source (recom-
mended voltage level is approximately 1Vp-p) to the
oscillator inputs (Figure 7).
Output Data Format
The conversion results are output on a 6-bit-wide data
bus. Data is latched into the ADC output latch following
a pipeline delay of one clock cycle (Figure 8). Output
data is clocked out of the ADC’s data output pins (D0
through D5) on the rising edge of the clock output
(DCLK), with a DCLK-to-data propagation delay (t
PD ) of
3.0ns. The MAX1011 outputs are +3.3V CMOS-logic
compatible.
Transfer Function
Figure 9 shows the MAX1011’s nominal transfer function.
Output coding is offset binary with 1LSB = FSR / 63.
___________Applications Information
The MAX1011 is designed with separate analog and
digital power-supply and ground connections to isolate
high-current digital noise spikes from the more sensi-
tive analog circuitry. The high-current digital output
ground (OGND) and analog ground (GND) should be
at the same DC level, connected at only one location
on the board. This will provide best noise immunity and
improved conversion accuracy. Use of separate
ground planes is strongly recommended.
The entire board needs good DC bypassing for both
analog and digital supplies. Place the power-supply
bypass capacitors close to where the power is routed
onto the board, i.e., close to the connector. 10µF elec-
trolytic capacitors with low-ESR ratings are recom-
mended. For best effective bits performance, minimize
capacitive loading at the digital outputs. Keep the digi-
tal output traces as short as possible.
The MAX1011 requires a +5V ±5% power supply for
the analog supply (V
CC ) and a +3.3V ±300mV power
supply connected to V CCO for the logic outputs.
Bypass each of the V CC supply pins to its respective
GND with high-quality ceramic capacitors located as
close to the package as possible (Table 2). Consult the
evaluation kit manual for a suggested layout and
bypassing scheme.
Low-Power, 90Msps, 6-Bit ADC
8 _______________________________________________________________________________________
Figure 7. External Clock Drive Circuit
MAX1011
CLK
DRIVER
TNK-
V CLK
V CLK = 300mV p-p TO 1.25V p-p
TNK+
50 Ω
50 Ω
Z 0 = 50 Ω
50 Ω
0.1 µ F
0.1 µ F
0.01µF Oscillator/Clock
47pF Digital Output
9
16
13
BYPASS
TO GND/
OGND
(PIN)
10
6
17
0.01µF Converter 14
V CC /
V CCO
(PIN)
11
SUPPLY
FUNCTION
0.01µF Analog Inputs
CAPACITOR
VALUE
Table 2. Bypassing Guide
Figure 6. Tank Resonator Oscillator
MAX1011
CLK
DRIVER
VARACTOR DIODE PAIR IS M/A-COM MA4ST079CK-287
(SOT23 PACKAGE)
INDUCTOR COILCRAFT 1008HS-221.
V TUNE = 0V TO 8V
f OSC = 70MHz TO 109MHz
TNK-
TNK+
V TUNE
220nH 5pF
47pF
47pF
47k
47k
10k