tripath technology, inc. - techn ical information 1 FILTER board ? revised 03-00 FILTER board instructions for use of the FILTER board for tripath amplifiers technical information revised march 2000 reference: excerpt from application note 4 copyright 1997-2000 tripath technol ogy, inc. all rights reserved tripath recommends the use of an output FILTER to remove displaced harmonics generated by the switching amplifier, which are present outside of the audio band. this FILTER board allows users to test thd and thd+n with equipment that lacks a 20khz or 30khz in ternal FILTER. the FILTER board should be placed between the test equipment and the amplifier output as follows: attach a load across the output jacks of one channel of the amplifier board. connect the in+ and in- terminals of the FILTER board across the load. connect the FILTER board?s power terminals to a dual 15v power supply. connect a 5v supply to drive the onboard gain changing relay circuit. note: the 5v supply is not needed when testing a ta1101b or ta2020-020. connect the thd+n test equipment to the 20khz or 30khz FILTER output. apply power to the tripath co mponent and then the FILTER board. apply test signals to the tripath component. make the measurements at the output of the tripath FILTER board. figure 3: recommended test setup for measuring a class-t amplifier . . . . tripath FILTER board ++ + 15v 5v 5v out- r l in+ 10k pot vr1 20khz rev h out+ 15v 30khz v- v+ gnd tripath eval board in- vr2 10k pot thd+n test equipment
tripath technology, inc. - techn ical information 2 FILTER board ? revised 03-00 there are two outputs on the FILTER card: 20khz and 30khz. the 20khz output is the standard output. the 30khz FILTER output has been included for compliance with the eiaj testing standard. they will yield the similar results. the FILTER board comes calibrated for use with the tripath ta1101b or ta2020-020 amplifier. there are two variable resistors, vr1 and vr2, that the us er may need to adjust when testing with ta101x based amplifiers: vr1 adjusts common mode rejection. this board come s calibrated from the fact ory, but if the input attenuation circuit is changed (when using power supplies greater than + 40v), vr1 may need to be trimmed. to calibrate it, apply the same 1v rms si ne wave in phase to both i nputs. look at the output with a scope and trim vr1 until the output is minimized. vr2 is a potentiometer that forms a voltage divider that allows the user to set the gain change trip point to maximize the performance of the FILTER board. the onboard relay allows for two different FILTER board gains depending on the input signal level at in+. the first range is a fixed 6 db attenuation caused by the combination of r100 and r102 on in+, and r103 and r105 on in-. the attenuation factor of the second range is determined by the addi tional parallel resistance seen by the inputs when the relay is closed (r101 on in+, r104 on in-). the value of vr2 determines when the FILTER board will switch from range 1 to range 2. assuming a gate th reshold of 2v for q1, vr2 should be adjusted to about 1500 ohms. this attenuation will cause the rela y to trip (therefore switching the FILTER board gain) before the input op amp starts to overload. table 1 is used to choose an appropriate attenuation factor for the second gain range. the required attenuation factor is supply voltage dependant. the additional attenuation makes sure that the op amps on the FILTER board do not clip with large input signals. vpp is the magni tude of positive supply in a traditional split supply, single ended amplifier confi guration (i.e. ta010xa designs). see table 1 for r101/r104 resistor value selection. amplifier loaded supply voltage resistor value ( ? ) vpp < 40v 49.9k* 40 < vpp < 50v 24.9k 50 < vpp < 60v 20.0k 60 < vpp < 70v 15.0k 70 < vpp < 80v 12.1k 80 < vpp < 90v 10.0k table 1: r101/r104 resistor value selection *the FILTER board comes stuffed with 49.9k ? for r101/r104.
tripath technology, inc. - techn ical information 3 FILTER board ? revised 03-00 when your analyzer?s standard thd+n test is perform ed, the results will meet or exceed tripath?s published specs and will be valid for comparison with non-class-t amplifiers. typical thd+n performance for a tripath ta1101b amplif ier is shown below in figure 4. figure 4: typical thd+n versus output power performance for ta1101b contact information tripath technology, inc 2560 orchard parkway, san jose, ca 95131 408.750.3000 - p 408.750.3001 - f for more sales information, please visit us @ www.tripath.com/cont_s.htm for more technical information, please visit us @ www.tripath.com/data.htm thd +n v e r su s ou t p u t po w e r 0.01 0.1 1 10 0.1 1 10 output power (w) thd+n (%) v s = 12v r l = 8 ? a v = 11.7
1 2 3 4 a b c d 4 3 2 1 d c b a title number revision size a date: 19-feb-2001 sheet of file: c:\temp1\newfol~2\fltrinpt.sch drawn by: c101 10uf, 25v c103 10uf, 25v in+ banana in- banana r105 49.9k r102 49.9k 3 2 1 8 4 6 5 7 v+ v- u1a opa2604 vcc vee r107 4.99k r108 4.99k r111 10k r109 10k r106 10k vr1 10k pot 2 3 1 8 4 6 5 7 v+ v- u2a opa2604 r110 4.99k vcc vee conout conout c110 0.1uf c111 0.1uf vcc vcc gnd gnd by-pass capacitors v- banana v+ banana vcc vee adjust vr1 to minimize output with common mode signal at in+ and in- gnd gnd c100 10uf, 25v c102 10uf, 25v gnd banana gnd r100 49.9k r103 49.9k gnd vr2 10k pot r112 10k c106 10uf, 25v + - rly1 relay-dpst r101 49.9k r104 49.9k gnd pos_inp pos_inp r113 ns gnd d1 1n4148 r114 0 gnd r115 100k c108 100uf, 25v c109 1uf, 25v 5v banana 5v q1 2n7000 5v c107 10uf, 25v c112 0.1uf c113 0.1uf vee vee gnd gnd c105 100pf c104 100pf adjust vr2 to set gain change trip point input section with gain change circuit r101 / r104 resistor value selection table amplifier loaded supply voltage resistor value vpp<=40v 49.9k 40 1 2 3 4 5 6 a b c d 6 5 4 3 2 1 d c b a title number revision size b date: 19-feb-2001 sheet of file: c:\temp1\newfol~2\fltrstge.sch drawn by: conout r14 1.05k r15 1.96k r16 1.05k 2 3 1 8 4 6 5 7 v+ v- u3a opa2604 c17 1500pf c18 1500pf vcc r17 1k c16 0.01uf 2nd order 20 khz lpf q = .527 2nd order 20khz lpf q = .682 vee r19 2.67k r18 1.4k 21out r20 1.4k c19 0.01uf r21 1k c20 270pf c21 1500pf 22out 2 3 1 8 4 6 5 7 v+ v- u5a opa2604 vcc vee r22 3.83k r23 7.15k c22 0.01uf r25 1k r24 3.83k c23 100pf c24 100pf 20k-out gnd 2nd order 20khz lpf q = 2.04 conout r26 698 r27 1.30k r28 698 2 3 1 8 4 6 5 7 v+ v- u4a opa2604 c26 1500pf c27 1500pf vcc r29 1k c25 0.01uf 2nd order 30 khz lpf q = .527 2nd order 30khz lpf q = .681 vee r31 1.78k r30 931 31out r32 931 c28 0.01uf r33 1k c29 270pf c30 1500pf 32out 2 3 1 8 4 6 5 7 v+ v- u6a opa2604 vcc vee r34 2.55k r35 4.75k c31 0.01uf r37 1k r36 2.55k c32 100pf c33 100pf 30k-out gnd 2nd order 30khz lpf q = 2.04 conout conout c3 0.1uf c4 0.1uf vcc vcc gnd gnd by-pass capacitors c5 0.1uf c6 0.1uf vcc vcc gnd gnd bnc 30khz bnc(rp) bnc 20khz bnc(rp) r38 0 r39 1k gnd gnd gnd r40 0 r41 1k gnd c7 0.1uf c8 0.1uf vee vee gnd gnd c9 0.1uf c10 0.1uf vee vee gnd gnd 20khz / 30khz FILTER stage
bill of material for amplifier FILTER board revb used part type designator footprint part field 1 ==== ========== ==================== ============ ================= 3 0 r114 r38 r40 1206 1%, metal film 6 0.01uf c16 c19 c22 c25 c28 1206 5%, npo c31 12 0.1uf c10 c110 c111 c112 1206 5%, npo c113 c3 c4 c5 c6 c7 c8 c9 2 1.05k r14 r16 1206 1%, metal film 1 1.30k r27 1206 1%, metal film 2 1.4k r18 r20 1206 1%, metal film 1 1.78k r31 1206 1%, metal film 1 1.96k r15 1206 1%, metal film 1 100k r115 1206 5%, npo 6 100pf c104 c105 c23 c24 1206 5%, npo c32 c33 1 100uf, 25v c108 radpo.10ax34 20%, electrolytic 4 10k r106 r109 r111 r112 1206 5%, npo 2 10k pot vr1 vr2 vr7 bourns 6 10uf, 25v c100 c101 c102 c103 sm d size 20%, tantalum c106 c107 6 1500pf c17 c18 c21 c26 c27 1206 5%, npo c30 8 1k r17 r21 r25 r29 r33 1206 1%, metal film r37 r39 r41 1 1n4148 d1 1206 5%, npo 1 1uf, 25v c109 radpo.10ax34 20%, electrolytic 2 2.55k r34 r36 1206 1%, metal film 1 2.67k r19 1206 1%, metal film 2 270pf c20 c29 1206 5%, npo 1 2n7000 q1 to92 fairchild 2 3.83k r22 r24 1206 1%, metal film 1 4.75k r35 1206 1%, metal film 3 4.99k r107 r108 r110 1206 5%, npo 6 49.9k r100 r101 r102 r103 1206 5%, npo r104 r105 2 698 r26 r28 1206 1%, metal film 1 7.15k r23 1206 1%, metal film 2 931 r30 r32 1206 1%, metal film 6 banana 5v gnd in+ in- v+ v- gbna002 * 2 bnc(rp) 20khz 30khz gbnc001 * 1 ns r113 1206 5%, npo 6 opa2604 u1 u2 u3 u4 u5 u6 so-8 burr brown 1 relay-dpst rly1 rlydpst hamlin
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