Download: APPLICATION NOTE A wide-band class-A linear power amplifier (174 − 230 MHz) with two transistors BLV33 ECO7904

APPLICATION NOTE A wide-band class-A linear power amplifier (174 − 230 MHz) with two transistors BLV33 ECO7904,

CONTENTS

1 ABSTRACT 2 INTRODUCTION 3 DESIGN OF THE AMPLIFIER 4 ADJUSTMENTS OF THE AMPLIFIER 5 ASSEMBLING OF THE AMPLIFIER AND MECHANICAL DATA 6 MEASURED RESULTS 7 CONCLUSION 8 REFERENCES 1998 Mar 23 2, 1 ABSTRACT For application in driver or final stages of TV-transposers in band III (174 − 230 MHz) a linear wideband power amplifier has been designed with 2 transistors BLV33, coupled by means of 3 dB −90° hybrids. Each transistor is adjusted in class-A at VCE = 25 V and IC = 3.25 A. A demonstration model showed a peak sync output power of 40 W at a 3-tone I.M. distortion between −56 and −58 dB. At this power level the cross-modulation varied from 6 to 7.5%. The power gain is between 8.35 and 8.6 dB. 2 INTRODUCTION For application in T.V. transposers and transmitters for band III a wideband linear power amplifier has been designed with 2 transistors BLV33, coupled by means of 3 dB −90° hybrids. Each transistor is adjusted in class-A at VCE = 25 V and IC = 3.25 A. 3 DESIGN OF THE AMPLIFIER For class-A operation the BLV33 is specified at VCE = 25 V, IC = 3.25 A. The corresponding typical gain, input and load impedance are given below: Table 1 FREQ. GAIN INPUT IMPEDANCE LOAD IMPEDANCE (MHz) (dB) (Ω) (Ω) 174 11.3 0.68 + j1.20 2.70 + j1.19 202 10.1 0.68 + j1.43 2.30 + j0.87 230 9.08 0.68 + j1.64 1.99 + j0.52 A computer-aided circuit design, carried out by Mr. Hilbers (Central Application Laboratory) indicated a gain of 9.1 dB ±0.1 dB and V.S.W.R. figures of 4.3 (170 MHz), 2.78 (202 MHz) and 1.18 at 230 MHz for a single amplifier. To obtain a high linear output and at the same time good input and output matching (V.S.W.R. ≤ 1.2) 3 dB −90° hybrids are used. The reflected input power will be absorbed in the 50 Ω resistor, matching the isolated port (see Fig.1). There are some small differences (value and place of chip capacitors) between the theoretical design and practical circuit. For detailed information on computer-aided design see Refs 1 and 2. Mainly due to the insertion loss of the 3 dB hybrids the gain drops from 9 to 8.5 dB. The transistors used in this particular amplifier are typical products, measured in a narrow band test amplifier and specified as follows: VCE = 25 V − IC = 3.25 A − Th = 70 °C 1998 Mar 23 3, Table 2 Transistor type BLV33 Batch no. MD 8-14 no 5 MD 8-14 no 10 Vision frequency 224.25 MHz Output power (peak sync) 22.9 W 22.6 W Intermodulation product −55 dB −55 dB Gain 9.03 dB 9.11 dB 4 ADJUSTMENTS OF THE AMPLIFIER The amplifier consists of two equal BLV33 branches (see Fig.1) and both transistors are separately biased at VCE = 25 V, IC = 3.25 A. A schematic diagram and lay-out of the bias unit is given in Fig.2. Each branch was adjusted for maximum and flat gain by means of a high power sweep with a frequency range from 170 to 230 MHz. The output power of the amplifier was levelled at 40 W which means about 50% of the D.C. input power. After that, both branches are coupled by means of 3 dB −90° hybrids, input and output matching of the complete amplifier are adjusted below a V.S.W.R. of 1.2 with the aid of capacitors C1-C2-C37-C38 as shown in Fig.1. 5 ASSEMBLING OF THE AMPLIFIER AND MECHANICAL DATA Due to the dimensions of the p.c. board (220 × 210 mm) 2 extruded blackened aluminium heatsinks (cat. no. 56293) are screwed together. The transistors are screwed on an aluminium plate (thickness 12 mm) which on its turn is screwed on the heatsink. Special attention has been paid to the surface finishing to keep the thermal resistance as low as possible. Figure 3 showed the p.c. board and lay-out of the amplifier. Dimensions: l = 224 mm − w = 223 mm − h = 113 mm. Weight: 7.5 kg. 6 MEASURED RESULTS Table 3 Frequency range 170 to 230 MHz Output power (peak sync) 30 W 40 W 50 W I.M. distortion −60 dB −56 dB −54 dB; note 1 Cross modulation 3% 6/7.5% 10/15.5%; note 2 Output power for 1 dB gain 100 W compression Gain at 40 W output level 8.5 dB ±0.1 dB Input and output V.S.W.R. ≤1.2 Ambient temp. 25 °C Heatsink temp. 65 °C Transistor stud temp. 85 °C Notes 1. Vision carrier −8 dB, sound carrier −7 dB, side signal −16 dB, zero dB corresponds to peak sync level; fsound = fvision + 5.5 MHz, fsideband = fvision − 1 MHz to fvision + 6 MHz. 2. Vision carrier 0 dB, sound carrier −7 dB: voltage variation of sound carrier (%) when the vision carrier is switched from −20 dB to 0 dB; fsound = fvision + 5.5 MHz. 1998 Mar 23 4, In Fig.4 the typical results of crossmodulation and intermodulation measurements on a demonstration amplifier have been given. Figures 5 and 6 show the S-parameters of the complete amplifier. The measuring set-up is depicted in Fig.7. 7 CONCLUSION Two transistors BLV33, coupled by means of 3 dB −90° hybrids, can deliver an output power of typ. 40 W with an associated gain of 8.5 dB. Required D.C. input power approx. 165 W. Using a high power sweep with adjustable transistor output power levelling provides a suitable method to adjust a linear wideband power amplifier. 8 REFERENCES Ref. 1: G.L. Matthaei − Tables of Chebyshev Impedance Transforming Networks of Low-Pass Filter Form. Proceedings of the IEEE August 1964, pp. 939 − 963. Ref. 2: A.H. Hilbers and M.J. Köppen − A wide-band linear power amplifier (470 − 860 MHz) with two transistors BLW34. C.A.B. report ECO7901. 1998 Mar 23 5, handbook, full pagewidth 1998 Mar 23 6 This text is here in white to force landscape pages to be rotated correctly when browsing through the pdf in the Acrobat reader.This text is here in _white to force landscape pages to be rotated correctly when browsing through the pdf in the Acrobat reader.This text is here inThis text is here in white to force landscape pages to be rotated correctly when browsing through the pdf in the Acrobat reader. white to force landscape pages to be ... Vb Vc C25 R3 C19 C26 C13 C27 L3 L9 C5 C9 C14 C21 C31 L7 C3 L4 L10 L13 L15 L19 L1 L21 BLV L1733 C6 C10 C15 C22C32 C35 C1 R5 R6 C37 input 50 Ω in 0° −90° iso H1 H2 iso output−90° 0° in 50 Ω C2 R1 R2 C38 C7 C11 C16 C23 C33 C36 L8L5 L11 L14 L16 L20C4 L2 L18 L22BLV33 C8 C12 C17 C24C34 L12 L6 C28 C18 C29 R4 C20 C30 Vb Vc MGP988 Fig.1 Band III Class A linear power amplifier (170 − 230 MHz)., Table 4 Parts list: Band III class A linear power amplifier (170 − 230 MHz) C1 = C38 1.5 pF chip capacitor C2 = C3 = C4 = C37 5.6 pF chip capacitor C5 = C8 = C32 = C33 1.8 to 10 pF film dielectric trimmer (cat. no. 222280905002) C6 = C7 = C35 = C36 220 pF chip capacitor C9 = C10 = C11 = C12 18 pF chip capacitor C13 = C18 = C27 = C28 1000 pF chip capacitor C14 = C15 = C16 = C17 100 pF chip capacitor C19 = C20 = C26 = C29 330 nF metallized film capacitor (cat. no. 222235225334) C21 = C23 68 pF chip capacitor C22 = C24 56 pF chip capacitor C25 = C30 10 µF (40 V) electrolytic capacitor (cat. no. 222212117109) C31 = C34 22 pF chip capacitor (chip capacitors: ATC type 100B − C − MSX − 500) R1 = R2 = R5 = R6 100 Ω power metal film resistor, PR52 type (cat. no. 232219231001) R3 = R4 10 Ω carbon resistor, CR68 type (cat. no. 23222141309) H1 = H2 3 dB −90° coupler model no. 10262 −3, range 125 − 250 MHz, Anaren Microwave Inc. L1 = L2 25 nH 2 turns enamelled Cu wire (1 mm); int. diam. 5 mm; length 5 mm; leads 2 × 3 mm L3 = L6 90 nH 5 turns closely wound enamelled Cu wire (1 mm); int. diam. 4.5 mm; leads 2 × 9 mm L4 = L5 60 Ω stripline; w = 2 mm; l = 30 mm L7 = L8 30 Ω stripline; w = 6 mm; l = 11 mm L9 = L12 20 nH Cu strip (1 mm); l = 17 mm; h = 5 mm; w = 4 mm L10 = L11 30 Ω stripline; w = 6 mm; l = 8 mm L13 = L14 30 Ω stripline; w = 6 mm; l = 14 mm L15 = L16 30 Ω stripline; w = 6 mm; l = 4 mm L17 = L18 22 nH 2 turns closely wound Cu wire (1.5 mm); int. diam. 4.5 mm; leads 2 × 3 mm L19 = L20 30 Ω stripline; w = 6 mm; l = 6 mm L21 = L22 50 Ω stripline; w = 3 mm; l = 15 mm The striplines are printed on double Cu-clad printed circuit board with epoxy fibre-glass dielectric (εr = 4.5); thickness 1/16 inch. 1998 Mar 23 7, handbook, full pagewidth Vs (+ 27 V) R5 R6 D2 e R7 b C4 TR1 BD136 R1 c Vc Vce = 25 V C1 C2 D1 C3 R2

V

R3 bR8 R9 BLV33 R4 R10 MGP997 handbook, full pagewidth 55 R5 C1 C2 R6 R7 C4 Vs D2 Vc C3 72 e R2 c R1 b D1 R8 Vb R3 R9 R4 R10 MGP998 Fig.2 Class A bias circuit for a single transistor BLV33. 1998 Mar 23 8, Table 5 Parts list: Class A bias circuit for a single transistor BLV33 R1 150 Ω carbon resistor CR25 type R2 100 Ω preset potentiometer CTP10 type R3 10 Ω carbon resistor CR25 type R4 1000 Ω carbon resistor CR25 type R5 = R6 = R7 1.8 Ω rectangular wirewound resistor EH707 type R8 = R9 180 Ω carbon resistor CR25 type R10 33 Ω carbon resistor CR25 type C1 = C3 100 nF metallized film capacitor C2 100 pF ceramic capacitor C4 10 µF 40 V electrolytic capacitor D1 BZY 88 (3V3) D2 BY 206 T1 BD 136 1998 Mar 23 9, handbook, full pagewidth 220 MGP989 Fig.3 P.C. Board and 2× BLV33 amplifier lay-out. 1998 Mar 23 10, MGP991 handbook, full pagewidth crossmod. (%) 0 dB

P

−7 dB o sync = 12 ∆V (%) 50 W −20 dB 40 W 30 W 168 175 182 189 196 203 210 217 f (MHz) 224 MGP992 −44 handbook, full pagewidth intermod. product 0 dB = Po sync (dB) −7 dBintermod. −8 dB −16 dB −46 product −48 Po sync = −50 60 W −52 −54 50 W −56 40 W −58 −60 30 W −62 168 175 182 189 196 203 210 217 f (MHz) 224 Vision carrier level: −20 dB/0 dB. Sound carrier level: −7 dB. Sync level: 0 dB. Fig.4 Crossmodulation and intermodulation products of the 2× BLV33 wideband Band III power amplifier. 1998 Mar 23 11, MGP993 handbook, halfpage (dB) 8.5 |S21| 7.5 130 150 170 190 210 230 250 (MHz) a. Forward transducer gain. MGP994 handboo(kd, hBa)lfpage 0 V.S.W.R. −10 2 1.5 −20 1.2 1.1 −30 −40 −50 |S11| −60 130 150 170 190 210 230 250 (MHz) b. Input voltage standing wave ratio. Fig.5 2× BLV33 wideband Band III power amplifier. 1998 Mar 23 12, MGP995 handboo(kd, hBa)lfpage −10 −20 −30 −40 −50 |S12| −60 130 150 170 190 210 230 250 (MHz) a. Reverse transducer gain. MGP996 handboo(kd, hBa)lfpage 0 V.S.W.R. −10 2 1.5 −20 1.2 1.1 −30 −40 −50 |S22| −60 130 150 170 190 210 230 250 (MHz) b. Output voltage standing wave ratio. Fig.6 2× BLV33 wideband Band III power amplifier. 1998 Mar 23 13, handbook, full pagewidth 1998 Mar 23 14 This text is here in white to force landscape pages to be rotated correctly when browsing through the pdf in the Acrobat reader.This text is here in _white to force landscape pages to be rotated correctly when browsing through the pdf in the Acrobat reader.This text is here inThis text is here in white to force landscape pages to be rotated correctly when browsing through the pdf in the Acrobat reader. white to force landscape pages to be ...

COAX

50 Ω SWITCH 8554L HP435A SPECTRUM WATT ANALYZER METER POWER POWER DIVIDER BAND III DIVIDER 20 20ATT. ATT. WIDEBAND dB dB 50 Ω POWER AMPLIFIER 50 Ω 50 Ω 50Ω3dB - 180° D.U.T. × ATT. (100W) ATT.

HYBRID

BLV33 10 6 COAX COAX HP778D HP778DSWITCH SWITCH dB dB CD ATT. DIRECT. COUPLER DIRECT. COUPLER 50-450 Ω 10 dB

ALC

CIRCULATOR RANGES: 170 to 200 MHz 6 VAR. VAR.190 to 230 MHz dB ATT. ATT. BLV33 10 S.M.L.U. AMPLIFIER dB R.F. GEN. COAX 50 Ω 50 Ω 50 Ω DETECTOR VAR. ATT. BLV33 10 S.M.L.U. 20 dB AMPLIFIER dB R.F. GEN. SWOB III PM5171 D.C. AMPLIFIER 50 Ω 50 Ω 50 Ω 50 Ω 50 Ω VAR. SWEEP ALC ATT. S.M.L.U. S.M.L.U. BLV33 BLV33 10 S.M.L.U. SWEEP R.F. GEN. AMPLIFIER AMPLIFIER dB R.F. GEN. 50 Ω 50 Ω 50 Ω POWER SWEEP TEST SET-UP 170 to 230 MHz 3-TONE TEST SET-UP MGP990 Fig.7 Test set up 2× BLV33 Band III power amplifier.,

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