
31
0860E–BDC–05/07
e2v semiconductors SAS 2007
TS8388B
8.3.2
Differential vs. Single-ended Analog Input Operation
The TS8388B can operate at full speed in either differential or single-ended configuration.
This is explained by the fact the ADC uses a high input impedance differential preamplifier stage, (pre-
ceeding the sample and hold stage), which has been designed in order to be entered either in differential
mode or single-ended mode.
This is true so long as the out-of-phase analog input pin V
INB is 50 terminated very closely to one of the
neighboring shield ground pins (52, 53, 58, 59) which constitute the local ground reference for the
inphase analog input pin (V
IN).
Thus the differential analog input preamplifier will fully reject the local ground noise (and any capacitively
and inductively coupled noise) as common mode effects.
In typical single-ended configuration, enter on the (V
IN) input pin, with the inverted phase input pin (VINB)
grounded through the 50
termination resistor.
In single-ended input configuration, the in-phase input amplitude is 0.5V peak to peak, centered on 0V
(or -2 dBm into 50
). The inverted phase input is at ground potential through a 50 termination resistor.
However, dynamic performances can be somewhat improved by entering either analog or clock inputs in
differential mode.
8.3.3
Typical Single-ended Analog Input Configuration
Figure 8-2.
Typical Single-ended Analog Input Configuration
Note:
Since VIN and VINB have a double pad architecture, a 50
reverse termination is needed. For the CBGA
package, this reverse termination is already on package.
8.4
Clock Inputs (CLK) (CLKB)
The TS8388B can be clocked at full speed without noticeable performance degradation in either differen-
tial or single-ended configuration.
This is explained by the fact the ADC uses a differential preamplifier stage for the clock buffer, which has
been designed in order to be entered either in differential or single-ended mode.
Recommended sinewave generator characteristics are typically –120 dBc/Hz phase noise floor spectral
density, at 1 kHz from carrier, assuming a single tone 4 dBm input for the clock signal.
8.4.1
Single-ended Clock Input (Ground Common Mode)
Although the clock inputs were intended to be driven differentially with nominal –0.8V/–1.8V ECL levels,
the TS8388B clock buffer can manage a single-ended sinewave clock signal centered around 0V. This is
the most convenient clock input configuration as it does not require the use of a power splitter.
50
(external or
on package)
1 M
3 pF
-250
250
500 mV
t
[mV]
VIN
VIN =
±250 mV = 500 mV diff
VIN or VINB double pad (pins 54, 55 or 56, 57)
VIN or VINB
50
reverse termination
500 mV
Full Scale
analog input
VINB = 0V
VINB