PAC80 Lattice Semiconductor Corp., PAC80 Datasheet - Page 11

• Manufacturer Part Number: PAC80
• Description: In-system Programmable Analog Circuit
• Manufacturer: Lattice Semiconductor Corp.

Differential I/O . Differential peak-peak voltage is deter-
mined by knowing the signal extremes on both differential
input or output pins. For example, if V(+) equals 4V and
V(-) equals 1V, the differential voltage is defined as V(+)
- V(-) = Vdiff, or 4V - 1V = +3V. Since either polarity can
exist on differential I/O pins, it is also possible for the
opposite extreme to exist and would mean when V(+)
equals 1V and V(-) equals 4V, the differential voltage is
now 1V - 4V = -3V. To calculate the differential peak-peak
voltage or full signal swing, the absolute difference be-
tween the two extreme Vdiff’s is calculated. Using the
previous examples would result in |(+3V) - (-3V)| = 6V. It
can be immediately seen that true differential signals
result in a doubling of usable dynamic range. For more
explanation of this and other differential circuit benefits,
please refer to application note AN6019.
Single-ended Input . To connect the ispPAC80 differen-
tial input to a single-ended signal, one of the differential
inputs needs to be connected to a DC bias, preferably
VREF
have a DC bias equal to the DC level of the other input.
Since the input voltage is defined as V
common mode level is ignored. The signal information is
only present on one input, the other being connected to
a voltage reference.
Single-ended Output . Connecting the output to a single-
ended circuit is simpler still. Simply connect one-half of
the differential output, but not the other. Either output
conveys the signal information, just at half the magnitude
of the differential output. The DC level of the single-
ended output will be VREF
coupled and is at a DC potential other than VREF
load draws a constant current. Using one of the differen-
tial outputs halves the available output voltage swing
(3V
amount available for voltage swing is reduced. The
output is capable of 10mA, so any DC current raises the
minimum allowable load impedance.
Input Common-Mode Voltage Range
For the ispPAC80, both maximum input signal range and
corresponding common-mode voltage range are a func-
tion of the input gain setting. The maximum input voltage
times the gain of an individual PACblock cannot exceed
the output range of that block or clipping will occur. The
maximum guaranteed input range is 1V to 4V, with an
extended typical range of 0.7V to 4.3V for a 5V supply
voltage.
Theory of Operation (Continued)
p-p
OUT
versus 6V
. The input signal must either be AC coupled or
p-p
). If the load requires DC current, the
OUT
. If the load is not AC
IN+
- V
OUT
IN-
, the
, the
11
The input common-mode voltage is V
When the value of V
restrictions other than the previously mentioned clipping
consideration. This is easily achieved when the input
signal is true differential and referenced to 2.5V.
When V
one, distortion will occur when the maximum input limit is
reached for a particular gain. The lowest V
gain setting is expressed by the formula, V
+ 0.584G·V
peak input voltage, expressed as |V
highest V
nominal supply voltage.
In Table 4, the maximum V
range is given. If the maximum V
equivalent or greater value under the appropriate gain
column and the widest range for V
horizontally across in the left-most two columns. Only a
V
free performance. Conversely, if the maximum V
range is known, the largest acceptable peak value of V
can be found in the corresponding gain column. All
values of V
mance.
Table 4. Input Common-Mode Voltage Range
Limitations
*Peak input voltage for guaranteed performance at a given gain setting.
CM
1.000
1.100
1.200
1.300
1.400
1.500
1.600
1.700
1.800
1.900
2.000
2.100
2.200
2.300
2.400
2.426
2.500
V
CM-
range equal to or less than this will give distortion-
CM
CM
Input Voltage Magnitude (Volts-Peak)
Specifications ispPAC80
is not 2.5V and the gain setting is greater than
IN
IN
4.000
3.900
3.800
3.700
3.600
3.500
3.400
3.300
3.200
3.100
3.000
2.900
2.800
2.700
2.600
2.574
V
2.500
where G is the gain setting and V
is V
less than this will give full rated perfor-
CM+
CM+
CM
3.000*
= 5.0V - V
0.557
0.728
0.899
1.071
1.242
1.413
1.584
1.756
1.927
2.098
2.270
2.441
2.612
2.783
2.955
3.126
is 2.5V, there are no further input
G=1
IN
for a given V
1.500*
0.278
0.364
0.450
0.535
0.621
0.707
0.792
0.878
0.964
1.049
1.135
1.220
1.306
1.392
1.477
1.563
G=2
CM–
IN
CM
IN+
is known, find the
CM
= (V
where 5V is the
0.600*
0.111
0.146
0.180
0.214
0.248
0.283
0.317
0.351
0.385
0.420
0.454
0.488
0.522
0.557
0.591
0.625
- V
G=5
CM+
will be found
CM
CM–
CM–
IN–
for a given
+ V
| and the
= 0.675V
to V
IN
0.300*
G=10
0.056
0.073
0.090
0.107
0.124
0.141
0.158
0.176
0.193
0.210
0.227
0.244
0.261
0.278
0.295
0.313
CM-
is the
CM+
)/2.
CM
IN