Application Note, Click to open in new window

DESIGN APPLICATION NOTE --- AN012
SGA-6589 Wideband (50-1000 MHz) Driver Circuit
Abstract
New Silicon / Germanium amplifier gain blocks
exhibit a combination of wide bandwidth, high
gain,IP3 and low noise figure. The SGA6589 is a
medium power gain block for which a versatile,
wideband RF driver application circuit has been
developed.
Introduction
The SGA-6589 (datasheet # EDS-101268) is a SiGe
medium power (P1dB = +21 dBm) wideband
cascadable gain block. It exhibits a combination of
high gain, P1dB, IP3 and a wide useful frequency
range. It has a characteristic gain roll-off versus
frequency of about 4 dB between 50 and 1000 MHz.
This is corrected using the application circuit
topology shown in Figure 1 below. Circuit
components RA1-3,CC1,CC3,RS1 and RS2 were
selected to optimize gain flatness and input/output
return loss. RS2 is also selected to improve the
margin of unconditional stability for the amplifier.
Bias chokes LB1 and LB2 are selected for high
impedance over the entire frequency band. The
circuit below operates with a 9 volt supply and draws
80 mA. It is characterized for the 50 - 1000 MHz
frequency range.
Notes:
1.0 LB1 & LB2 shall be TOKOLL2012-FHR47J (390 nH)
Rdc= 1.8 Ohms, SRF= 300 MHz
2.0 All resistors and capacitors are 0603 style unless
otherwise stated.
3.0 All 0603 capacitors have an implied series
inductance of approx. 0.8 nH
4.0 Microstrip transmission line segments (Z1 - Z4)
between components are calculated based on
wavelength of 500 MHz signal on FR4 board material
with dielectric constant of 4.1 and microstrip width and
height dimensions of W=.061 inch and h=.030 inch.
Design / Performance Summary
The circuit layout and performance data are shown
on pages 2 and 3. The circuit was constructed on
our standard 89 package evaluation board
according to the schematic shown in Figure 1. The
performance highlights to be notedPreliminary
are :
• >21 dB gain and <1 dB total gain variation
over the 50-1000 MHz frequency range.
• +18 to +19 dBm P1dB.
• > +30 dBm IP3,+45 dBm IP2
• > 18 dB input / 20 dB output return loss over
the 50-1000 MHz frequency range.
• Unconditionally stable from DC to beyond 6
GHz.
Applications
• VCO buffer amplifier
• High output cable driver
• High Level, high linearity LO driver
• Power amplifier pre-driver
• Final PA /antenna driver for low power,short-haul
communications transmitters
RB2
(1/4Watt, style 1206)
+9V
RB1
91Ω
(1/4Watt, style 1206)
Cd2
0.1 uF
Cd1
0.1 uF
RB4
470 Ω
RB3
470Ω
CC1
6.8 pF
LB2
390 nH
390 nH
RA1
RA3
390 Ω
390 Ω
Z2
0.1 uF
Zc
Length
(Degrees)
@500 MHz
Z1
50
6
Z2
50
2.4
Z3
50
6.7
Z4
50
3.7
CC3
12 pF
Rs1
Z1
39 Ω
Ref.
Des.
LB1
SGA-6589
CC2
RA2
RF input
Microstrip specifications
91Ω
Z3
RS2
CC4
18 Ω
0.1 uF
Z4
6.8 Ω
RF Output
SGA-6589 @ 50-1000 MHz Wideband Driver Application Circuit
Figure 1
The information provided herein is believed to be reliable at press time RFMD
.
assumes no responsibility for inaccuracies or omissions. RFMD assumes no responsibility for
the use of this information, and all such information shall be entirely at the user’s own risk. Prices and specifications are subject to change without notice. No patent rights or licenses to any of the circuits described
herein are implied or granted to any third party.RFMD does not authorize or warrant any RFMD product for use in life-support devices and/or systems.
Copyright 2002 RFMD All worldwide rights reserved.
522 Almanor Ave., Sunnyvale, CA 94085
Phone: (800) SMI-MMIC
1
http://www.RFMD.com
EAN-101613 Rev B
DESIGN APPLICATION NOTE --- AN012
SGA-6589 Wideband (50-1000 MHz) Driver Circuit
Parts List
2
Cd
1
RB
1
Cd
2
RB
4
SGA6589
RA
3
RA
2
Cc
2
LB
2
RB
3
Rs
2
LB
1
Rs
1
Cc
3
IN
60
Cc
4
OUT
P1dB, IP3, IP2 Level
(dBm)
RA
1
CC1
CC2,4
CC3
Cd1,2
RA1,3
RA2
RS1
RS2
RB1,2
RB3,4
LB1,2
+Vd
sRB
Gn
d
Cc
1
REF. DESIG. PART TYPE
RFMD
ECB-100607 Rev-A
SOT-89 Eval Board
Notes:
Board Material: FR4, ε =4.1
Dielectric thickness = 30 mils
Metal Thickness: 1 Oz (1.4 mil)
Backside fully plated
CAP.
CAP.
CAP.
CAP.
RES.
RES.
RES.
RES.
RES.
RES.
IND.
VALUE
PART NUMBER / STYLE
6.8 pF
0.1 uF
12 pF
0.1 uF
390 Ohms
39 Ohms
6.8 Ohms
18 Ohms
91 Ohms
470 Ohms
390 nH
0603 package (ROHM MCH 18)
0603 package (ROHM MCH 18)
0603 package (ROHM MCH 18)
0603 package (ROHM MCH 18)
0603 package
0603 package
0603 package
0603
package
Preliminary
1206 package (1/4 Watt)
0603 package
TOKO LL2012-FHR390J
Plot of P1dB,IP3,IP2,NF vs. Frequency for SGA6589
Wideband Driver Application Circuit
27
24
50
40
18
15
IP3
30
12
20
10
P1dB
9
NF
6
3
0
0
Figure 2
21
IP2(low side)
Noise Figure (dB)
Application Circuit Board Layout,
for 50-1000 Mhz
(Reference Figure 1 Schematic.)
200
400
600
800
0
1200
1000
Frequency (MHz)
Plot of S21,S11,S22 vs. Frequency for SGA6589
(De-embedded Device)
25
-12
S11(dB)
15
-6
-18
10
-24
5
-30
1000
0
200
400
600
800
0
20
-12
15
-18
S11(dB)
10
5
0
200
5
1
0.8
4
0.8
DELTA dev
0.6
2
0.4
K factor
3
0.2
K dev
0
3000
4000
-30
1000
800
1
5000
0
6000
K Factor
4
2000
600
Plot of K and DELTA Stability Factors vs. Frequency for the 501000 MHz SGA- 6589 Application Circuit.
DELTA factor
5
1000
400
Frequency (MHz)
Plot of K and DELTA Stability Factors vs. Frequency for the Deembedded SGA- 6589
0
-24
S22(dB)
Frequency (MHz)
1
-6
S21(dB)
S11,S22 (dB)
S22(dB)
20
30
Kapp
3
0.6
2
0.4
DELTAapp
1
0
0
Frequency (MHz)
1000
2000
3000
4000
5000
DELTA Factor
S21(dB)
25
0
S21 (dB)
S21(dB)
S11,S22 (dB)
30
Plot of S21, S11, S22 vs. Frequency for
SGA-6589 50-1000 MHz Wideband Driver Circuit
0.2
0
6000
Frequency (MHz)
The information provided herein is believed to be reliable at press time RFMD
.
assumes no responsibility for inaccuracies or omissions. RFMD assumes no responsibility for
the use of this information, and all such information shall be entirely at the user’s own risk. Prices and specifications are subject to change without notice. No patent rights or licenses to any of the circuits described
herein are implied or granted to any third party.RFMD does not authorize or warrant any RFMD product for use in life-support devices and/or systems.
Copyright 2002 RFMD All worldwide rights reserved.
522 Almanor Ave., Sunnyvale, CA 94085
Phone: (800) SMI-MMIC
2
http://www.RFMD.com
EAN-101613 Rev B
DESIGN APPLICATION NOTE --- AN012
SGA-6589 Wideband (50-1000 MHz) Driver Circuit
Plot of Reverse Isolation vs. Frequency for 50-1000 MHz
Driver Circuit and De-embedded Device.
-10
Reverse Gain (dB)
-15
Preliminary
-20
-25
S12 (de-embedded device)
-30
S12(apps.circuit)
-35
-40
0
200
400
600
800
1000
Frequency (MHz)
Plot of Group Delay vs. Frequency for SGA-6589
50-1000 MHz Applications Circuit
1000
900
Group Delay (Picoseconds)
Discussion of Performance
By splitting the gain compensation circuitry
appropriately between the input and output,
gain flatness was achieved without extreme
degradation of either noise figure (from input
loss) or P1dB and IP3 (from output loss). This
also facilitated stability and I/O return loss
improvements. The bias circuit contains two
390 nH coils (in series) to ensure adequately
high impedance over the entire decade of
bandwidth. Their self-resonant frequencies are
about 300 MHz. This allows consistently high
P1dB and IP3 over this frequency range. The
unusual parallel resistor/inductor configuration
of the bias components was implemented to
prevent series resonant interaction between
the parasitic capacitances of the coils from
creating low impedance “notch” frequencies
which result in gain and group delay
discontinuities at the resonant frequencies. As
can be seen from the plots, these parameters
vary smoothly with frequency. The high reverse
isolation of this circuit also makes it particularly
suitable as a VCO buffer to minimize “loadpull” effects. Reverse isolation is in excess of
30 dB out to 1GHz.
800
700
600
500
400
τ 21
300
200
100
0
0
100
200
300
400
500
600
Frequency (MHz)
700
800
900
1000
Conclusion
This application note has shown a simple solution using passive components to greatly improve the gain
flatness, stability and input / output return loss of the SGA-6589 SiGe cascadable gain block. This was
achieved while maintaining relatively high absolute gain, high P1dB, IP3 and moderate noise figure. The
result is a robust , wideband driver circuit with numerous applications in areas where high signal output
levels are required to drive loads which exhibit extreme variations in impedance. The techniques utilized
here may be applied to compensate similar high gain SiGe devices which exhibit sharp frequency response
roll-off such as the SGA-6586.
We hope that this application note and the excellent devices made byRFMD will assist
you in achieving your design goals.
The information provided herein is believed to be reliable at press time RFMD
.
assumes no responsibility for inaccuracies or omissions. RFMD assumes no responsibility for
the use of this information, and all such information shall be entirely at the user’s own risk. Prices and specifications are subject to change without notice. No patent rights or licenses to any of the circuits described
herein are implied or granted to any third party.RFMD does not authorize or warrant any RFMD product for use in life-support devices and/or systems.
Copyright 2002 RFMD All worldwide rights reserved.
522 Almanor Ave., Sunnyvale, CA 94085
Phone: (800) SMI-MMIC
3
http://www.RFMD.com
EAN-101613 Rev B
Similar pages