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