The Communications Edge TM
VG025
High Linearity Variable Gain Amplifier
Product Information
Application Circuit Configurations
Circuit Board Material: .014” FR-4, 4 layers, .062” total thickness
The WJ VG025 variable gain amplifier can operate over a very
broad range of frequencies (50 - 2200MHz), but needs specific
matching circuits for specific bands of interest. At the maximum
gain state, reasonable matching is only available for about ±10% of
the reference frequency. The amplifier operates with a typical
current of 150 mA at +5 V while the attenuator current can be varied
from 0 to 30 mA, while maintaining constant OIP3 and P1dB. The
RF matching of the VG025 for the entire frequency range can be
accomplished with the systematic adjustment of only a few parts.
The RF matching is not influenced by different attenuator drive
greater than the Reference frequency (this allows for good isolation
and inductor variation). Next choose L3 and C9 for interstage
matching. C9 is only needed for lower frequencies and determines
the low frequency roll off of the gain. L3 will have dominant
control over the input and output return losses at maximum gain
state (0 mA gain control pin current). C2 is needed to resonate the
package parasitics to achieve the maximum attenuation values with
attenuator current. With attenuator control pin current of 26 mA, C2
can be chosen to provide maximum attenuation. See the chart below
for suggested component values and predicted performance at
methods provided there is adequate decoupling of the attenuator bias. various reference frequencies.
Component values can be
This reference application circuit uses voltage applied between 0
and 4.5V onto the Vctrl as shown on the schematic above. The R2 is
a current limiting resistor to help linearize the drive of the attenuator
and give better attenuator current control.
interpolated for reference frequencies not listed.
For lower frequencies the lumped element values can be used and
the layout with unplaced component pads does not greatly affect the
RF performance of the circuit. For frequencies greater than 500
MHz, component size and trace length have more influence on
circuit performance. Smaller components and shorter trace lengths
reduce the affects of the external component parasitics and
interaction with the multichip module parasitics.
To properly design the VG025 for an application, pick the frequency
of interest. Choose blocking capacitor values which give RF
impedance of less than 3 ohms. Choose the RF chokes for the
largest inductance while still having resonant frequency about 30%
Reference Frequency
MHz
pF
pF
μF
pF
pF
nH
nH
nH
Ω
240
1000
0 Ω
.01
DNP
1.2
220
47
DNP
DNP
120
20
15.4
11
11
21.8
42
4.5
800
56
27
.01
DNP
DNP
22
8.2
82
1850
56
3.6
.01
DNP
DNP
12
DNP
33
DNP
120
12
8.6
11
7.7
22
40
7.9
1960
56
3.6
.01
DNP
DNP
12
DNP
33
DNP
120
14
8.4
12
6.5
22
40
8.1
2140
56
3.6
.01
DNP
DNP
12
DNP
33
DNP
120
13
8.4
11
5.6
22
40
8.2
C1, C5
C2
C3, C4
C6
C9
L1, L2
L3
L4
R1
R2
DNP
120
21
Ω
Attenuation Range
Maximum Gain
Input Return Loss
Output Return Loss
Output P1dB
Output IP3
Noise Figure
dB
dB
dB
dB
dBm
dBm
dB
15
6.3
7.6
21.3
39
5.3
DNP = Do Not Place (Component is not used in the design)
Specifications and information are subject to change without notice
Page 2 of 7 January 2006
WJ Communications, Inc • Phone 1-800-WJ1-4401 • FAX: 408-577-6621 • e-mail: sales@wj.com • Web site: www.wj.com
WJCI [ WJ COMMUNICATION. INC. ]
