MAX1438 Datasheet, PDF (14/22 Pages) Maxim Integrated Products – Octal, 12-Bit, 65Msps, 1.8V ADC with Serial LVDS Outputs Serial LVDS Outputs

Octal, 12-Bit, 65Msps, 1.8V ADC
with Serial LVDS Outputs
Connect ≥ 1µF (10µF typ) capacitors to GND from
REFP and REFN and a ≥ 1µF (10µF typ) capacitor
between REFP and REFN as close to the device as
possible on the same side of the PC board.
External Reference Mode
The external reference mode allows for more control
over the MAX1438 reference voltage and allows multi-
ple converters to use a common reference. Connect
REFADJ to AVDD to disable the internal reference.
Apply a stable 1.18V to 1.30V source at REFIO. Bypass
REFIO to GND with a ≥ 0.1µF capacitor. The REFIO
input impedance is > 1MΩ.
Clock Input (CLK)
The MAX1438 accepts a CMOS-compatible clock sig-
nal with a wide 20% to 80% input clock duty cycle.
Drive CLK with an external single-ended clock signal.
Figure 2 shows the simplified clock input diagram.
Low clock jitter is required for the specified SNR perfor-
mance of the MAX1438. Analog input sampling occurs
on the rising edge of CLK, requiring this edge to pro-
vide the lowest possible jitter. Jitter limits the maximum
SNR performance of any ADC according to the follow-
ing relationship:
SNR = 20 × log
⎛
⎝⎜
2×
1
π × f_IN
⎞
× t_J⎠⎟
where f_IN represents the analog input frequency and t_J
is the total system clock jitter.
PLL Inputs (PLL1, PLL2, PLL3)
The MAX1438 features a PLL that generates an output
clock signal with 6 times the frequency of the input
clock. The output clock signal is used to clock data out
of the MAX1438 (see the System Timing Requirements
section). Set the PLL1, PLL2, and PLL3 bits according
to the input clock range provided in Table 1.
AVDD
CVDD
CLK
GND
MAX1438
DUTY-CYCLE
EQUALIZER
Table 1. PLL1, PLL2, and PLL3
Configuration Table
PLL1
PLL2
PLL3
0
0
0
0
0
1
0
1
0
0
1
1
1
0
0
1
0
1
1
1
0
1
1
1
INPUT CLOCK RANGE
(MHz)
MIN
MAX
45.0
65.0
32.5
45.0
22.5
32.5
16.3
22.5
11.3
16.3
8.1
11.3
5.6
8.1
4.0
5.6
System Timing Requirements
Figure 3 shows the relationship between the analog
inputs, input clock, frame-alignment output, serial-clock
output, and serial-data output. The differential analog
input (IN_P and IN_N) is sampled on the rising edge of
the CLK signal and the resulting data appears at the
digital outputs 6.5 clock cycles later. Figure 4 provides
a detailed, two-conversion timing diagram of the rela-
tionship between the inputs and the outputs.
Clock Output (CLKOUTP, CLKOUTN)
The MAX1438 provides a differential clock output that
consists of CLKOUTP and CLKOUTN. As shown in Figure
4, the serial output data is clocked out of the MAX1438 on
both edges of the clock output. The frequency of the out-
put clock is 6 times the frequency of CLK.
Frame-Alignment Output (FRAMEP, FRAMEN)
The MAX1438 provides a differential frame-alignment
signal that consists of FRAMEP and FRAMEN. As
shown in Figure 4, the rising edge of the frame-align-
ment signal corresponds to the first bit (D0) of the 12-
bit serial data stream. The frequency of the frame-
alignment signal is identical to the frequency of the
input clock.
Serial Output Data (OUT_P, OUT_N)
The MAX1438 provides its conversion results through
individual differential outputs consisting of OUT_P and
OUT_N. The results are valid 6.5 input clock cycles
after the sample is taken. As shown in Figure 3, the out-
put data is clocked out on both edges of the output
clock, LSB (D0) first. Figure 5 provides the detailed ser-
ial-output timing diagram.
Figure 2. Clock Input Circuitry
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