SPT7814BCU Ver la hoja de datos (PDF) - Signal Processing Technologies
Número de pieza
componentes Descripción
Fabricante
SPT7814BCU Datasheet PDF : 11 Pages
| |||
An example of a reference driver circuit recommended is
shown in figure 2. IC1 is REF-03, the +2.5 V reference with a
tolerance of 0.6% or ± 0.015 V. The potentiometer R1 is
10 kΩ and supports a minimum adjustable range of up to
150 mV. IC2 is recommended to be an OP-07 or equivalent
device. R2 and R3 must be matched to within 0.1% with good
TC tracking to maintain a 0.3 LSB matching between VFT and
VFB. If 0.1% matching is not met, then potentiometer R4 can
be used to adjust the VFB voltage to the desired level. R1 and
R4 should be adjusted such that VST and VSB are exactly
+2.0 V and -2.0 V respectively.
The analog input range will scale proportionally with respect
to the reference voltage if a different input range is required.
The maximum scaling factor for device operation is ± 20% of
the recommended reference voltages of VFT and VFB. How-
ever, because the device is laser trimmed to optimize perfor-
mance with ± 2.5 V references, the accuracy of the device will
degrade if operated beyond a ± 2% range.
The following errors are defined:
+FS error = top of ladder offset voltage = ∆(+FS -VST+1 LSB)
-FS error=bottom of ladder offset voltage=∆(-FS -VSB -1 LSB)
where the +FS (full scale) input voltage is defined as the
output transition between 1-10 and 1-11 and the -FS input
voltage is defined as the output transition between 0-00 and
0-01.
ANALOG INPUT
VIN1 and VIN2 are the analog inputs. Both inputs are tied to
the same point internally. Either one may be used as an
analog input sense and the other for an input force. The inputs
can also be tied together and driven from the same source.
The full scale input range will be 80% of the reference voltage
or ±2 volts with VFB=-2.5 V and VFT=+2.5 V.
The drive requirements for the analog inputs are minimal
when compared to conventional Flash converters due the
SPT7814’s extremely low input capacitance of only 5 pF and
very high input resistance of 300 kΩ. For example, for an input
signal of ± 2 V p-p with an input frequency of 10 MHz, the peak
output current required for the driving circuit is only 628 µA.
CLOCK INPUT
The clock inputs (CLK,CLK ) are designed to be driven differ-
entially with ECL levels. The clock may be driven single
ended since CLK is internally biased to -1.3 V. CLK may be
left open, but a .01 µF bypass capacitor to AGND is recom-
mended. As with all high speed circuits, proper terminations
are required to avoid signal reflections and possible ringing
that can cause the device to trigger at an unwanted time.
The CLK pulse width (tpwH) must be kept between 10 ns and
300 ns to ensure proper operation of the internal track-and-
hold amplifier. (See timing diagram.) When operating the
SPT7814 at sampling rates above 3 MSPS, it is recom-
mended that the clock input duty cycle be kept at 50% to
optimize performance. (See graph.) The analog input signal
is latched on the rising edge of the CLK.
SNR vs Clock Duty Cycle
59
57
55
53
51
DCuyctyle=
tpwH
tpwL
49
tpwH tpwL
47
45
43
30
35
40
45
50
55
60
65
70
75
Duty Cycle of Positive Clock Pulse (%)
DIGITAL OUTPUTS
The format of the output data (D0-D9) is straight binary.
These outputs are ECL with the output circuit shown in
figure 4. The outputs are latched on the rising edge of CLK
with a propagation delay of 4 ns. There is a one clock cycle
latency between CLK and the valid output data (see timing
diagram). These digital outputs can drive 50 ohms to ECL
levels when pulled down to -2 V. The total specified power
dissipation of the device does not include the power used by
these loads. The additional power used by these loads can
vary between 10 and 300 mW typically (including the overrange
load) depending on the output codes. If lower power levels
are desired, the output loads can be reduced, but careful
consideration to the capacitive loads in relation to the oper-
ating frequency must be considered.
Table II - Output Data Information
ANALOG INPUT
>+2.0 V + 1/2 LSB
OVERRANGE
D1O
1
OUTPUT CODE
D9-DO
11 1111 1111
+2.0 V -1 LSB
0.0 V
O
11 1111 111Ø
O
ØØ ØØØØ ØØØØ
-2.0 V +1 LSB
O
OO OOOO OOOØ
<-2.0 V
O
OO OOOO OOOO
(Ø indicates the flickering bit between logic 0 and 1).
SPT
8
SPT7814
3/11/97
Share Link: 