THS3215 Datasheet, PDF (49/71 Pages) Texas Instruments – THS3215 650-MHz, Differential to Single-Ended DAC Output Amplifier

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THS3215
SBOS780A – MARCH 2016 – REVISED APRIL 2016
Device Functional Modes (continued)
9.4.1.3 External Connection
In the configuration shown in Figure 92, the bias to PATHSEL (pin 4) is changed in order to select the external
input of the OPS. The external D2S output drives a low insertion loss, third-order Bessel filter. The filter in this
example is designed with a low frequency insertion loss of 1.55 dB and f_–3dB = 50 MHz, and results in an
additional insertion loss of 1 dB at 30 MHz. The OPS gain is slightly increased to recover the filter loss, in order
to give an input to output gain of 5 V/V. Using an interstage filter between the D2S and the OPS improves the
step response by reducing the overshoot. The filter in this example has a relatively low cutoff frequency but if the
application requires it, use a filter with a higher cutoff frequency.
49.9
Differential
V_IN
49.9
VPATHSEL > 1.3 V
16
15
1
50 k
2 x1
50 k
x1
50
+
250
500
3 x1
14
100
13
18.5 k
102
12
205
49.9
11
AV= 5 V/V
To
50-Ÿ /RDG
10
18.5 k
4
5
6
90.9
1-dB loss
at 30 MHz
9
464
7
8
50-MHz, Low Insertion Loss
3rd-Order Bessel Filter
250 nH
11 pF
56 pF
Figure 92. External Path Configuration With Interstage Low-Pass Filter
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