RF Amplifier Design Using HFA3046, HFA3096, HFA3127, HFA3128 Transistor Arrays TM Application Note November 1996 Introduction AN9315.1 HFA3046 This application note is focused on exploiting the RF design capabilities of HFA3046/3096/3127/3128 transistor arrays. Detailed design procedures, using these transistor arrays, for a matched (800MHz to 2500MHz) high-gain low-noise amplifier and a 10MHz to 600MHz wideband feedback amplifier are described. 1 2 Q1 Q5 3 4 1 TABLE 1. UHF-1 DEVICE CHARACTERISTIC 2 PNP 8 8 V BVCBO, MIN 12 10 V BVEBO, MIN 5.5 4.5 V ICBO 0.1 0.1 nA hFE 70 40 CCB 500 600 fF 9 5.5 GHz P1DB (IC = 10mA, VCE = 5V, fO = 1GHz) 7.6 6.2 dBm IP3 (IC = 10mA, VCE = 5V, fO = 1GHz) 17.6 16.2 dBm NF (RS = 50Ω, IC = 5mA, VCE = 3V, fO = 1GHz) 3.5 3.0 dB 10 Q1 3 Q2 Q5 6 7 8 Q3 Q4 12 Q4 8 11 10 7 8 Q3 14 13 Q2 Q3 HFA3127 4 15 Q5 6 9 7 16 NC Q1 3 11 Q4 NC 5 fT 13 2 4 6 UNITS BVCEO, MIN 1 5 The HFA3046, HFA3096, HFA3127, HFA3128 transistor arrays are fabricated in a complementary bipolar bonded wafer silicon-on-insulator (SOI) technology, dubbed UHF-1 [1]. All four products make use of the same die, which has both NPN and PNP transistors on it. Figure 1 shows the pinouts of the four different products. Typical NPN and PNP transistor characteristics are shown in Table 1. NPN 14 12 Q2 5 PARAMETERS HFA3096 9 HFA3128 16 1 15 2 16 14 3 13 4 12 NC 5 12 11 6 11 10 7 9 8 Q1 15 14 Q2 Q5 13 10 Q3 Q4 9 FIGURE 1. PINOUTS OF HFA3046/3096/3127/3128 SOIC PACKAGED TRANSISTOR ARRAYS Circuit Design High-Gain Low-Noise Amplifier One important design requirement for an RF amplifier is the accurate control of input and output impedance levels. This is especially important if the amplifier is to interface with matched source and load impedances. Based on S-parameter measurements, for a common-emitter configuration, transistors of HFA3127 exhibit a prematched condition on the input side over a wide range of frequencies. The package lead and bond wire inductances for these transistors make the input impedance close to 50Ω. For IC = 5mA - 10mA, VCE = 2V - 5V, the input VSWR of Q2 and Q5 was less than -10dB for frequencies of 800MHz to 3000MHz. Furthermore, for these transistors, a good output match, output VSWR < -10dB for frequencies 300MHz to 3000MHz, could be accomplished through bypassing the collector with a 100Ω resistor. As the single stage amplifiers built with Q2 and Q5 both show good input and output matching, they can be cascaded for higher gain without requiring an impedance transforming network. Figure 2 shows the final two stage amplifier. The advantage of this circuit is its simplicity. This design does not use any tuning inductors or capacitors which would tend to increase the cost of the circuit. Furthermore, this circuit accomplishes higher gain by cascading two amplifier stages built with integrated transistors. The SOI process has the advantage of lower DC and AC parasitic leakage currents as opposed to junction isolation, which leads to good isolation between transistors. Furthermore, an SOI process provides substantially lower collector to substrate capacitance, immunity to any possible latch-up between the devices, and superior radiation hardness. The HFA3127 is used for the two stage matched (800MHz to 2500MHz) high-gain amplifier design, while the HFA3096 is used for the 10MHz to 600MHz wideband feedback amplifier. 3-1 1-888-INTERSIL or 321-724-7143 | Intersil and Design is a trademark of Intersil Corporation. | Copyright © Intersil Corporation 2000 Application Note 9315 0 - R1 39kΩ R2 100Ω R3 39kΩ R4 100Ω C3 1nF C2 1nF Q5 Q2 RS 50Ω –5 INPUT VSWR (dB) VCC + VO RL 50Ω +VS IC = 5mA, VCC = 3V -10 –15 IC = 10mA, VCC = 5V –20 FIGURE 2. HIGH-GAIN LOW-NOISE AMPLIFIER REALIZED WITH HFA3127 From Figure 2, the noise figure of the whole circuit is mainly controlled by the noise characteristics of the transistor Q5. As shown in Figure 3D, this high-gain amplifier demonstrates good noise performance. For IC2 = IC5 = 5mA, the measured noise figure is 3.9dB at 900MHz, making this useful as a high-gain, low-noise amplifier. –25 0 1 2 3 FREQUENCY (GHz) FIGURE 3B. INPUT VSWR 0 OUTPUT VSWR (dB) Figure 3 shows the measured characteristics of the amplifier under two different bias conditions: VCC = 3V, IC2 = IC5 = 5mA; and VCC = 5V, IC2 = IC5 = 10mA. As can be seen from Figure 3, the input and output VSWR is less than -10dB for frequencies greater than 800MHz. The amplifier shows better performance at the expense of higher power dissipation (IC = 10mA and VCC = 5V) except the noise figure. For IC2 = IC5 = 10mA, the amplifier gains are 18.7, 8.8, and 6.6dB at frequencies of 900MHz, 1800MHz, and 2200MHz, respectively. -5 -10 IC = 5mA, VCC = 3V -15 IC = 10mA, VCC = 5V -20 The complete microstrip board layout is shown in Figure 4. A 0.031 inch thick FR-4 (G-10) glass epoxy board is used for the layout. The dielectric constant of the material is 4.7 at 1000MHz. 0 2 3 FREQUENCY (GHz) FIGURE 3C. OUTPUT VSWR 40 6 NOISE FIGURE (dB) 30 GAIN (dB) 1 IC = 10mA, VCC = 5V 20 10 IC = 5mA, VCC = 3V 5 IC = 10mA, VCC = 5V 4 IC = 5mA, VCC = 3V 0 0 1 2 FREQUENCY (GHz) FIGURE 3A. GAIN 3 3 0 0.5 1 FREQUENCY (GHz) 1.5 2 FIGURE 3D. NOISE FIGURE 3. MEASURED CHARACTERISTICS OF THE HIGH GAIN LOW-NOISE AMPLIFIER 3-2 Application Note 9315 Wideband Amplifier OUTPUT A well known simple amplifier configuration which achieves flat gain and broadband matching without losing excessive signal power is shown in Figure 6. The simultaneous use of both shunt and series feedback gives rise to broadband resistive input and output impedances [2, 3]. C3 THROUGH HOLE R4 CBP HFA3127 R3 R1 C1 INPUT C2 R2 CBP Figure 7 shows a similar version of the double feedback wideband amplifier circuit realized with the HFA3096. This design takes advantage of the PNP transistors (Q4 and Q5) available on the HFA3096, to bias amplifying transistor Q2 for good temperature stability. RF CBP VO RS LCHOKE + - VCC FIGURE 4. MICROSTRIP BOARD LAYOUT FOR THE HIGH-GAIN LOW-NOISE AMPLIFIER The key rule for the circuit board layout is to make the physical length of the conductors as short as possible where the RF signal is involved. Although it seems obvious, it is easy to forget that the impedance looking into a microstrip line, that has load attached at the end, can be totally different from the attached load impedance depending on the length of the microstrip line and frequency. Outside the RF signal path, it does not matter. At RF frequencies, the value of chip resistors, capacitors, and inductors should not be taken for granted. In general, the smaller the size of the component, the better the performance. However, it is important to evaluate the components before use. For the RF frequencies, these components can be evaluated easily using a network analyzer by mounting them as shown in Figure 5. The SMA connector itself contributes about 0.7pF of capacitance between the signal and ground terminals. CHIP COMPONENT CUT CENTER PINS FLUSH TO FLANGE SMA CONNECTOR FIGURE 5. A CHIP COMPONENT MOUNTED ON AN SMA CONNECTOR 3-3 VS RL RE FIGURE 6. SINGLE STAGE SHUNT AND SERIES FEEDBACK CIRCUIT R4 100Ω R1 2kΩ Q5 Q4 R2 15kΩ R3 1kΩ RF 240Ω + 5V - L1 1µH C3 1nF C1 1nF VO RL 50Ω Q2 C2 1nF RS 50Ω RE 5.1Ω +VS FIGURE 7. WIDEBAND AMPLIFIER REALIZED WITH HFA3096 The frequency response of the wideband amplifier is shown in Figure 8. As can be seen from Figure 8, the amplifier shows 10dB of flat gain with 600MHz bandwidth.The input and output matching is very good over the range of frequency where gains are flat. The low frequency performance is limited by the 1000pF capacitor. The microstrip board layout for the wideband amplifier is shown in Figure 9. A 0.031 inch thick FR-4 (G-10) glass epoxy board is used for the layout. Application Note 9315 0 15 -10 GAIN (dB) VSWR (dB) 10 OUTPUT VSWR -20 5 -30 INPUT VSWR -40 0 107 108 FREQUENCY (Hz) 109 107 108 109 FREQUENCY (Hz) FIGURE 8A. GAIN FIGURE 8B. INPUT-OUTPUT VSWR FIGURE 8. MEASURED CHARACTERISTICS OF THE WIDEBAND AMPLIFIER Summary A detailed process of designing a high-gain low-noise and a wideband amplifier using the Intersil UHF transistor arrays is summarized. VCC A two-stage, high-gain, low-noise amplifier built with the HFA3127 demonstrates 50Ω input and output impedance over a wide frequency range of 800MHz to 2500MHz without the use of external matching networks. The gain at 900MHz is in excess of 17dB with a noise figure of 3.9dB. THROUGH HOLE LCHOKE CBP R1 R4 A wideband amplifier built with the HFA3096 demonstrates excellent input and output matching with 10dB of constant gain. The -3dB bandwidth of this amplifier is 600MHz. PNP transistors available on the HFA3096 are used for temperature stable biasing of the amplifying transistor. R2 CBP OUTPUT L1 HFA3096 RE R 3 C1 C3 RF CBP C2 INPUT FIGURE 9. MICROSTRIP BOARD LAYOUT FOR THE WIDEBAND References [1] [1]C. Davis, et al, “UHF-1: A High Speed Complementary Bipolar Analog Process on SOI,” Proceeding of BCTM 92, pp260-263, Oct. 1992. [2] [2]J. B. Couglin, et al, “A Monolithic Silicon wideband Amplifier from DC to 1 GHz,” IEEE J. Solid-State Circuits, vol. SC-8, pp414-419, Dec. 1973. [3] [3]R. G. Meyer, et al, “A wideband Ultralinear Amplifier from 3 to 300 MHz,” IEEE J. Solid-State Circuits, vol. SC-9, pp167-175, Aug. 1974. All Intersil semiconductor products are manufactured, assembled and tested under ISO9000 quality systems certification. Intersil semiconductor products are sold by description only. Intersil Corporation reserves the right to make changes in circuit design and/or specifications at any time without notice. Accordingly, the reader is cautioned to verify that data sheets are current before placing orders. Information furnished by Intersil is believed to be accurate and reliable. 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