MAX108 Maxim, MAX108 Datasheet - Page 20

• Manufacturer Part Number: MAX108
• Description: 5V / 1.5Gsps / 8-Bit ADC with On-Chip 2.2GHz Track/Hold Amplifier
• Manufacturer: Maxim

±5V, 1.5Gsps, 8-Bit ADC with
On-Chip 2.2GHz Track/Hold Amplifier
Table 5. DC-Coupled Clock Drive Options
The clock inputs CLK+ and CLK- can be driven with
PECL logic if the clock inputs are AC-coupled. Under
this condition, connect CLKCOM to GNDI. Single-
ended ECL/PECL/sine-wave drive is also possible if the
undriven clock input is reverse-terminated to GNDI
through a 50Ω resistor in series with a capacitor whose
value is identical to that used to couple the driven
input.
The MAX108 features an internal 1:2 demultiplexer that
reduces the data rate of the output digital data to one-
half the sample clock rate. Demux reset is necessary
when interleaving multiple MAX108s and/or synchroniz-
ing external demultiplexers. The simplified block dia-
gram of Figure 1 shows that the demux reset signal path
consists of four main circuit blocks. From input to out-
put, they are the reset input dual latch, the reset
pipeline, the demux clock generator, and the reset out-
put. The signals associated with the demux reset opera-
tion and the control of this section are listed in Table 6.
The reset input dual-latch circuit block accepts differ-
ential PECL reset inputs referenced to the same V
power supply that powers the MAX108 PECL outputs.
For applications that do not require a synchronizing
reset, the reset inputs can be left open. In this case,
they will self-bias to a proper level with internal 50kΩ
resistors and 20µA current source. This combination
creates a -1V difference between RSTIN+ and RSTIN-
to disable the internal reset circuitry. When driven with
PECL logic levels terminated with 50Ω to (V
the internal biasing network can easily be overdriven.
Figure 14 shows a simplified schematic of the reset
input structure.
To properly latch the reset input data, the setup time
(t
respect to the rising edge of the sample clock. The tim-
ing diagram of Figure 15 shows the timing relationship
of the reset input and sampling clock.
20
SU
Single-Ended Sine Wave
Differential Sine Wave
Single-Ended ECL
Differential ECL
) and the data-hold time (t
______________________________________________________________________________________
CLOCK DRIVE
Demux Reset Operation
AC-Coupling Clock Inputs
Reset Input Dual Latch
-10dBm to +4dBm
-10dBm to +4dBm
HD
) must be met with
ECL Drive
ECL Drive
CLK+
CC
O - 2V),
CC
O
External 50Ω to GNDI
-10dBm to +4dBm
ECL Drive
Figure 14. Simplified Reset Input Structure
Figure 15. Reset Input Timing Definitions
CLK-
-1.3V
RSTIN+
RESET INPUTS ARE
ESD PROTECTED
(NOT SHOWN IN THIS
SIMPLIFIED DRAWING).
RSTIN-
50k
50%
t
20 A
SU
CLKCOM
GNDI
GNDI
50k
-2V
-2V
RSTIN+
RSTIN-
GNDD
50%
t
HD
50%
CLK+
CLK-
Figure 13a
Figure 13b
Figure 13c
Figure 13d
REFERENCE
V
CC
O