參數(shù)資料
型號: AD15700BCA
廠商: ANALOG DEVICES INC
元件分類: 模擬信號調(diào)理
英文描述: 1 MSPS 16-/14-Bit Analog I/O Port
中文描述: SPECIALTY ANALOG CIRCUIT, PBGA144
封裝: MO-205AC, CSPBGA-144
文件頁數(shù): 41/44頁
文件大?。?/td> 1100K
代理商: AD15700BCA
REV. A
AD15700
–41–
High Performance Single-Supply Line Driver
Even though the amplifier swings close to both rails, the amplifier
has optimum distortion performance when the signal has a common-
mode level halfway between the supplies and when there is about
500 mV of headroom to each rail. If low distortion is required in
single-supply applications for signals that swing close to ground,
an emitter follower circuit can be used at the amplifier output.
V
OUT
V
IN
49.9
200
2.49
2.49
49.9
10 F
5V
0.1 F
49.9
2N3904
Figure 43. Low Distortion Line Driver for Single-
Supply Ground Referenced Signals
2V
50mV
100
90
0%
10
1μs
0.5V
Figure 44. Output Signal Swing of Low Distortion
Line Driver at 500 kHz
+9dBm
V
START 0Hz
STOP 5MHz
Figure 45. THD of Low Distortion Line Driver at 500 kHz
Figure 43 shows the amplifier configured as a single-supply
gain-of-two line driver. With the output driving a back terminated
50
W
line, the overall gain from V
IN
to V
OUT
is unity. In addition
to minimizing reflections, the 50
W
back termination resistor pro-
tects the transistor from damage if the cable is short circuited.
The emitter follower, which is inside the feedback loop, ensures
that the output voltage from the amplifier stays about 700 mV
above ground. Using this circuit, very low distortion is attain-
able even when the output signal swings to within 50 mV of
ground. The circuit was tested at 500 kHz and 2 MHz. Figures 44
and 45 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).
Figures 46 and 47 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 (e.g., 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), so 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.
1.5V
50mV
100
90
0%
10
200ns
0.2V
Figure 46. Output Signal Swing of Low Distortion
Line Driver at 2 MHz
V
START 0Hz
STOP 20MHz
+7dBm
Figure 47. THD of Low Distortion Line Driver at 2 MHz
相關(guān)PDF資料
PDF描述
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