ADL5391ACPZ-WP(Rev0) Ver la hoja de datos (PDF) - Analog Devices
Número de pieza
componentes Descripción
Lista de partido
ADL5391ACPZ-WP Datasheet PDF : 16 Pages
| |||
Matching the Input/Output
The input and output impedance’s of the ADL5391 change over
frequency, making it difficult to match over a broad frequency
range (see Figure 15 and Figure 16). The evaluation board is
matched for lower frequency operation, and the impedance
change at higher frequencies causes the change in gain seen in
Figure 6. If desired, the user of the ADL5391 can design a
matching network to fit their application.
Wideband Voltage-Controlled Amplifier/Amplitude
Modulator
Most of the data for the ADL5391 was collected by using it as a
fast reacting analog VGA. Either X or Y inputs can be used for
the RF input (and the other as the very fast analog control),
because either input can be used from dc to 2 GHz. There is a
linear relationship between the analog control and the output of
the multiplier in the VGA mode. Figure 6 and Figure 7 show the
dynamic range available in VGA mode (without optimizing the
dc offsets).
The speed of the ADL5391 in VGA mode allows it to be used as
an amplitude modulator. Either or both inputs can have
modulation or CW applied. AM modulation is achieved by
feeding CW into X (or Y) and adding AM modulation to the Y
(or X) input.
Squaring and Frequency Doubling
Amplitude domain squaring of an input signal, E, is achieved
simply by connecting the X and Y inputs in parallel to produce
an output of E2. The input can be single-ended, differential, or
through a balun (frequency range and dynamic range can be
limited if used single ended).
When the input is a sine wave Esin(ωt), a signal squarer behaves
as a frequency doubler, because
[Esin(ωt)]2 = E 2 (1− cos(2ωt ))
(3)
2
Ideally, when used for squaring and frequency doubling, there is
no component of the original signals on the output. Because of
internal offsets, this is not the case. If Equation 3 were rewritten
to include theses offsets, it could separate into three output
terms (Equation 4).
[ ] Esin(ωt) + OFST ×[Esin(ωt) + OFST] =
E2
2
[cos(2ωt)]+
2 Esin(ωt )OFST
+
⎜⎜⎝⎛OFST 2
+
E2
2
⎟⎟⎠⎞
(4)
where:
The dc component is OFST2 + E2/2.
The input signal bleedthrough is 2Esin(ωt)OFST.
The input squared is E2/2[cos(2ωt)].
ADL5391
The dc component of the output is related to the square of both
the offset (OFST) and the signal input amplitude (E). The offset
can be found in Figure 4 and is approximately 20 mV. The
second harmonic output grows with the square of the input
amplitude, and the signal bleedthrough grows proportionally
with the input signal. For smaller signal amplitudes, the signal
bleedthrough can be higher than the second harmonic
component. As the input amplitude increases, the second
harmonic component grows much faster than the signal
bleedthrough and becomes the dominant signal at the output.
If the X and Y inputs are driven too hard, third harmonic
components will also increase.
For best performance creating harmonics, the ADL5391 should
be driven differentially. Figure 17 shows the performance of the
ADL5391 when used as a harmonic generator (the evaluation
board was used with R9 and R10 removed and R2 = 56.2 Ω). If
dc operation is necessary, the ADL5391 can be driven single
ended (without the dc blocks). The flatness of the response over
a broad frequency range depends on the input/output match.
The fundamental bleed through not only depends on the
amount of power put into the device but also depends on
matching the unused differential input/output to the same
impedance as the used input/output. Figure 18 shows the
performance of the ADL5391 when driven single ended
(without ac coupling capacitors), and Figure 19 shows the
schematic of the setup. A resistive input/output match were
used to match the input from dc to 1 GHz and the output from
dc to 2 GHz. Reactive matching can be used for more narrow
frequency ranges. When matching the input/output of the
ADL5391, care needs to be taken not to load the ADL5391 too
heavily; the maximum reference current available is 50 mA.
–15
–20
SECOND HARMONIC GAIN
–25
–30
–35
BLEEDTHRU GAIN
–40
–45
–50
–55
–60
THIRD HARMONIC GAIN
–65
10
100 200 300 400 500 600 700 800 900 1000
FREQUENCY (MHz)
Figure 17. ADL5391 Used as a Harmonic Generator
Rev. 0 | Page 11 of 16
Share Link: 