Datasheet

Data Sheet AD8031/AD8032
Rev. F | Page 17 of 20
Figure 50 and Figure 51 show the output signal swing and
frequency spectrum at 500 kHz. At this frequency, the output
signal (at V
OUT
), which has a peak-to-peak swing of 1.95 V
(50 mV to 2 V), has a THD of −68 dB (SFDR = −77 dB).
2V
50mV
10
0%
100
90
0.5V
1µs
01056-050
Figure 50. Output Signal Swing of Low Distortion Line Driver at 500 kHz
STOP 5MHz
VERTICAL SCALE (10dB/DIV)
START 0Hz
+9dBm
01056-051
Figure 51. THD of Low Distortion Line Driver at 500 kHz
Figure 52 and Figure 53 show the output signal swing and
frequency spectrum at 2 MHz. As expected, there is some
degradation in signal quality at the higher frequency. When the
output signal has a peak-to-peak swing of 1.45 V (swinging
from 50 mV to 1.5 V), the THD is −55 dB (SFDR = −60 dB).
This circuit could also be used to drive the analog input of a
single-supply, high speed ADC whose input voltage range is
referenced to ground (for example, 0 V to 2 V or 0 V to 4 V). In
this case, a back termination resistor is not necessary (assuming
a short physical distance from transistor to ADC); therefore, the
emitter of the external transistor would be connected directly to
the ADC input. The available output voltage swing of the circuit
would therefore be doubled.
50mV
10
0%
100
90
1.5V
0.2V 200ns
01056-052
Figure 52. Output Signal Swing of Low Distortion Line Driver at 2 MHz
VERTICAL SCALE (10dB/DIV)
+7dBm
START 0Hz STOP 20MHz
01056-053
Figure 53. THD of Low Distortion Line Driver at 2 MHz