Rainbow Electronics MAX108 - Manual (Page 23)

asserted, the auxiliary port contained “even” samples
while the primary port contained “odd” samples. After
the RSTOUT is deasserted (which marks the start of the
DREADY clock’s reset phase), note that the order of the
samples in the ports has been reversed. The auxiliary
port also contains an out-of-sequence sample. This is a
consequence of the “swallowed” clock cycle that was
needed to resynchronize DREADY to the reset phase.
Also note that the older sample data is always in the
auxiliary port, regardless of the DREADY phase.
These examples illustrate the combinations that result
with a reset input signal of two clock cycles. It is also
possible to reset the internal MAX108 demux success-
fully with a reset pulse of only one clock cycle, provid-
ed that the setup time and hold-time requirements are
met with respect to the sample clock. However, this is
not recommended when additional external demuxes
are used.
Note that many external demuxes require their reset
signals to be asserted while they are clocked, and may
require more than one clock cycle of reset. More impor-
tantly, if the phase of the DREADY clock is such that a
clock pulse will be “swallowed” to resynchronize, then
no reset output will occur at all. In effect, the RSTOUT
signal will be “swallowed” with the clock pulse. The
best method to ensure complete system reset is to
assert RSTIN for the appropriate number of DREADY
clock cycles required to complete reset of the external
demuxes.
Die Temperature Measurement
For applications that require monitoring of the die tem-
perature, it is possible to determine the die temperature
of the MAX108 under normal operating conditions by
observing the currents I
CONST and I PTAT , at contacts
ICONST and IPTAT. I CONST and I PTAT are two 100µA
(nominal) currents that are designed to be equal at
+27°C. These currents are derived from the MAX108’s
internal precision +2.5V bandgap reference. I
CONST is
designed to be temperature independent, while I PTAT is
directly proportional to the absolute temperature. These
currents are derived from PNP current sources refer-
enced from V
CC I and driven into two series diodes con-
nected to GNDI. The contacts ICONST and IPTAT may
be left open because internal catch diodes prevent sat-
uration of the current sources. The simplest method of
determining the die temperature is to measure each
MAX108
±5V, 1.5Gsps, 8-Bit ADC with
On-Chip 2.2GHz Track/Hold Amplifier
______________________________________________________________________________________ 23
Figure 19. Reset Output Timing in Demuxed DIV2 Mode (DREADY Realigned)
NOTE: DREADY PHASE WAS ADJUSTED TO MATCH THE RESET PHASE BY “SWALLOWING” ONE INPUT CLOCK CYCLE.
THE AUXILIARY PORT CONTAINS AN OUT-OF-SEQUENCE SAMPLE AS A RESULT OF THE DELAY.
CLK-
CLK+
t SU t
HD
n n+1 n+2 n+3 n+4 n+5 n+6 n+7 n+8 n+9 n+10 n+11 n+12 n+13
ADC SAMPLE NUMBER
ADC SAMPLES ON THE RISING EDGE OF CLK+
CLOCK PULSE “SWALLOWED”
OUT-OF-SEQUENCE SAMPLE
CLK
DREADY
DREADY+
DREADY-
RSTIN+
RSTIN-
RSTOUT+
RSTOUT-
RESET
INPUT
n-1 n+1
n-2
AUXILIARY
DATA PORT
PRIMARY
DATA PORT
n n+2
n+4
RESET OUT
DATA PORT