AD604-EVAL Analog Devices Inc, AD604-EVAL Datasheet - Page 21

• Manufacturer Part Number: AD604-EVAL
• Description: BOARD EVALUATION FOR AD604
• Manufacturer: Analog Devices Inc

Specifications of AD604-EVAL

• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

At 1 MHz, the attenuation is about −0.2 dB, increasing to −6 dB
at 10 MHz and −28 dB at 100 MHz. Signals less than approximately
1 MHz are not significantly affected.
Figure 49 shows the control voltage vs. the input power at 1 MHz
to the circuit shown in Figure 48; note that the AGC threshold is at
−95 dBm. The output signal level is set to 800 mV p-p by applying
−80 mV to the V
ULTRALOW NOISE, DIFFERENTIAL INPUT-
DIFFERENTIAL OUTPUT VGA
Figure 50 shows how to use both preamplifiers and DSXs to
create a high impedance, differential input-differential output
VGA. This application takes advantage of the differential inputs
to the DSXs. Note that the input is not truly differential in the
sense that the common-mode voltage needs to be at ground to
achieve maximum input signal swing. This has largely to do
with the limited output swing capability of the output drivers of
the preamplifiers; they clip around ±2.2 V due to having to drive
an effective load of about 30 Ω. If a different input common-mode
voltage needs to be accommodated, ac coupling (as in Figure 48)
is recommended. The differential gain range of this circuit runs
from 6 dB to 54 dB, which is 6 dB higher than each individual
channel of the AD604 because the DSX inputs now see twice
Figure 48. Modifications of the AGC Amplifier to Create 96 dB of Gain Range
Figure 49. Control Voltage vs. Input Power of the Circuit in Figure 48
4.5
4.0
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0.1µF
–100 –90 –80 –70 –60 –50 –40 –30 –20 –10
0
C5
499Ω
#2643000301
SET
R2
FAIR-RITE
connector.
FB
560pF
0.1µF
C3
C6
1MHz
P
10
11
12
1
2
3
4
5
6
7
8
9
IN
(dBm)
–DSX1
+DSX1
PAO1
FBK1
PAI1
COM1
COM2
PAI2
FBK2
PAO2
+DSX2
–DSX2
AD604
VOCM
GND1
VPOS
VNEG
VNEG
VPOS
GND2
VGN1
VREF
OUT1
OUT2
VGN2
24
23
22
21
20
19
18
17
16
15
14
13
0
10
Rev. G | Page 21 of 32
the signal amplitude compared with when they are driven
single-ended.
VIN+
Fig
a −20 dB attenuator formed between the 453 Ω resistors shown
in Figure 50 and the 50 Ω loads presented by the oscilloscope
plug-in. R1 and R2 are inserted to ensure a nominal load of 500 Ω
at each output. The differential gain of the circuit is set to 20 dB
by applying a control voltage, VGN, of 1 V; the gain scaling is
20 dB/V for a VREF of 2.500 V; the input frequency is 10 MHz
and the differential input amplitude is 100 mV p-p. The resulting
differential output amplitude is 1 V p-p as can be seen on the
scope photo when reading the vertical scale as 200 mV/div.
VIN–
0.1µF
0.1µF
ure 51 displays the output signals VOUT+ and VOUT− afte
Figure 50. Ultralow Noise, Differential Input-Differential Output VGA
C1
C4
100
NOTES
1. THE OUTPUT AFTER 10× ATTENUATER FORMED
0%
90
10
BY 453Ω TOGETHER WITH 50Ω OF 7A24 PLUG-IN.
0.1µF
C12
0.1µF
0.1µF
Figure 51. Output of VGA in Figure 50 for VGN = 1 V
C2
C3
20mV
20mV
C13
0.1µF
10
11
12
1
2
3
4
5
6
7
8
9
COM1
COM2
–DSX1
PAO1
FBK1
PAI1
PAI2
FBK2
PAO2
–DSX2
+DSX1
+DSX2
ALL SUPPLY PINS ARE DECOUPLED AS SHOWN.
FB
FB
AD604
+5V
–5V
VOCM
VNEG
VNEG
VGN1
GND1
VPOS
VPOS
GND2
VGN2
VREF
OUT1
OUT2
24
23
22
21
20
19
18
17
16
15
14
13
20ns
+5V
–5V
–5V
+5V
C5
0.1µF
0.1µF
0.1µF
C6
C7
453Ω
453Ω
R1
R2
ACTUAL
V
+500mV
–500mV
AD604
OUT
VREF
VOUT+
VOUT–
VG
,
r