J
Jeroen Belleman
Guest
We had a rainy weekend here and I decided to spend some
time simulating Battjes' Ft doubler and to compare it
with a more ordinary differential cascode amplifier
with similar gain and bias conditions.
I sort-of expected to find that the bandwidth of the
Ft doubler would roughly be twice that of the simple
differential stage, but I did not find that. In fact,
the bandwidth is about the same. I conclude that I
don't understand the point of the Ft doubler. What
gives?
Included below the .asc file of the Ft doubler. To
compare with a simple differential pair, just delete
one pair and tweak the resistor between the emitters
of the remaining pair to restore the gain. I get a
-3dB bandwidth of about 2.6GHz either way.
Jeroen Belleman
Version 4
SHEET 1 1256 680
WIRE 144 -416 -416 -416
WIRE 720 -416 144 -416
WIRE -416 -352 -416 -416
WIRE 144 -352 144 -416
WIRE 720 -352 720 -416
WIRE -416 -208 -416 -272
WIRE 720 -208 720 -272
WIRE 144 -160 144 -272
WIRE 720 -160 720 -208
WIRE 784 -112 208 -112
WIRE 816 -112 784 -112
WIRE 944 -112 896 -112
WIRE 1056 -112 1024 -112
WIRE 144 48 144 -64
WIRE 336 48 144 48
WIRE 720 48 720 -64
WIRE 720 48 512 48
WIRE 336 112 512 48
WIRE 528 112 336 48
WIRE 144 144 144 48
WIRE 336 144 336 112
WIRE 528 144 528 112
WIRE 720 144 720 48
WIRE -256 192 -288 192
WIRE -96 192 -176 192
WIRE 80 192 -16 192
WIRE 432 192 400 192
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WIRE 720 480 720 448
WIRE 720 480 624 480
WIRE 240 512 240 480
WIRE 624 512 624 480
WIRE 240 624 240 592
WIRE 624 624 624 592
FLAG -288 192 0
FLAG -416 -208 0
FLAG 240 624 0
FLAG 720 -208 out1
FLAG 624 624 0
FLAG 1056 192 0
FLAG 1056 -112 0
FLAG 432 432 0
SYMBOL npn 80 144 R0
SYMATTR InstName Q1
SYMATTR Value BFR92A
SYMBOL npn 400 144 M0
SYMATTR InstName Q2
SYMATTR Value BFR92A
SYMBOL res 704 -368 R0
SYMATTR InstName R2
SYMATTR Value 500
SYMBOL res 128 352 R0
SYMATTR InstName R3
SYMATTR Value 1200
SYMBOL voltage -416 -368 R0
SYMATTR InstName V1
SYMATTR Value 10V
SYMBOL voltage 240 608 R180
WINDOW 0 24 96 Left 2
WINDOW 3 24 16 Left 2
SYMATTR InstName V2
SYMATTR Value 5V
SYMBOL voltage -160 192 R90
WINDOW 3 24 152 Left 2
WINDOW 123 24 124 Left 2
WINDOW 39 0 0 Left 2
SYMATTR Value PULSE(-1m 1m 0 100p 100p 1n 2n)
SYMATTR Value2 AC 1
SYMATTR InstName V3
SYMBOL res 0 176 R90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R4
SYMATTR Value 50
SYMBOL res 912 176 R90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R5
SYMATTR Value 50
SYMBOL voltage 624 608 R180
WINDOW 0 24 96 Left 2
WINDOW 3 24 16 Left 2
SYMATTR InstName V4
SYMATTR Value 5V
SYMBOL npn 784 -160 M0
SYMATTR InstName Q3
SYMATTR Value BFR92A
SYMBOL voltage 928 -112 R270
WINDOW 0 32 56 VTop 2
WINDOW 3 -32 56 VBottom 2
WINDOW 123 0 0 Left 2
WINDOW 39 0 0 Left 2
SYMATTR InstName V6
SYMATTR Value 3
SYMBOL npn 208 -160 M0
SYMATTR InstName Q6
SYMATTR Value BFR92A
SYMBOL res 416 288 R0
SYMATTR InstName R8
SYMATTR Value {rb}
SYMBOL res 912 -128 R90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R9
SYMATTR Value 100
SYMBOL res 128 -368 R0
SYMATTR InstName R1
SYMATTR Value 500
SYMBOL npn 784 144 M0
SYMATTR InstName Q4
SYMATTR Value BFR92A
SYMBOL npn 464 144 R0
SYMATTR InstName Q5
SYMATTR Value BFR92A
SYMBOL res 320 352 R0
SYMATTR InstName R7
SYMATTR Value 1200
SYMBOL res 512 352 R0
SYMATTR InstName R6
SYMATTR Value 1200
SYMBOL res 704 352 R0
SYMATTR InstName R10
SYMATTR Value 1200
SYMBOL res 272 256 R90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R11
SYMATTR Value 240
SYMBOL res 656 256 R90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R12
SYMATTR Value 240
SYMBOL cap 304 320 R90
WINDOW 0 0 32 VBottom 2
WINDOW 3 32 32 VTop 2
SYMATTR InstName C1
SYMATTR Value 900f
SYMBOL cap 688 320 R90
WINDOW 0 0 32 VBottom 2
WINDOW 3 32 32 VTop 2
SYMATTR InstName C2
SYMATTR Value 900f
SYMBOL voltage 1040 192 R90
WINDOW 3 24 152 Left 2
WINDOW 123 24 124 Left 2
WINDOW 39 0 0 Left 2
SYMATTR Value PULSE(-1m 1m 0 100p 100p 1n 2n)
SYMATTR Value2 AC 1
SYMATTR InstName V5
TEXT 16 -520 Left 2 !;tran 5u
TEXT 8 -464 Left 2 !.ac dec 100 1k 4G
TEXT 336 -520 Left 2 !.param rb=50
TEXT 328 -464 Left 2 !;.step param rb list 5 50 500 5k
time simulating Battjes' Ft doubler and to compare it
with a more ordinary differential cascode amplifier
with similar gain and bias conditions.
I sort-of expected to find that the bandwidth of the
Ft doubler would roughly be twice that of the simple
differential stage, but I did not find that. In fact,
the bandwidth is about the same. I conclude that I
don't understand the point of the Ft doubler. What
gives?
Included below the .asc file of the Ft doubler. To
compare with a simple differential pair, just delete
one pair and tweak the resistor between the emitters
of the remaining pair to restore the gain. I get a
-3dB bandwidth of about 2.6GHz either way.
Jeroen Belleman
Version 4
SHEET 1 1256 680
WIRE 144 -416 -416 -416
WIRE 720 -416 144 -416
WIRE -416 -352 -416 -416
WIRE 144 -352 144 -416
WIRE 720 -352 720 -416
WIRE -416 -208 -416 -272
WIRE 720 -208 720 -272
WIRE 144 -160 144 -272
WIRE 720 -160 720 -208
WIRE 784 -112 208 -112
WIRE 816 -112 784 -112
WIRE 944 -112 896 -112
WIRE 1056 -112 1024 -112
WIRE 144 48 144 -64
WIRE 336 48 144 48
WIRE 720 48 720 -64
WIRE 720 48 512 48
WIRE 336 112 512 48
WIRE 528 112 336 48
WIRE 144 144 144 48
WIRE 336 144 336 112
WIRE 528 144 528 112
WIRE 720 144 720 48
WIRE -256 192 -288 192
WIRE -96 192 -176 192
WIRE 80 192 -16 192
WIRE 432 192 400 192
WIRE 464 192 432 192
WIRE 816 192 784 192
WIRE 944 192 896 192
WIRE 1056 192 1024 192
WIRE 144 272 144 240
WIRE 176 272 144 272
WIRE 336 272 336 240
WIRE 336 272 256 272
WIRE 528 272 528 240
WIRE 560 272 528 272
WIRE 720 272 720 240
WIRE 720 272 640 272
WIRE 432 304 432 192
WIRE 144 336 144 272
WIRE 240 336 144 336
WIRE 336 336 336 272
WIRE 336 336 304 336
WIRE 528 336 528 272
WIRE 624 336 528 336
WIRE 720 336 720 272
WIRE 720 336 688 336
WIRE 144 368 144 336
WIRE 336 368 336 336
WIRE 528 368 528 336
WIRE 720 368 720 336
WIRE 432 432 432 384
WIRE 144 480 144 448
WIRE 240 480 144 480
WIRE 336 480 336 448
WIRE 336 480 240 480
WIRE 528 480 528 448
WIRE 624 480 528 480
WIRE 720 480 720 448
WIRE 720 480 624 480
WIRE 240 512 240 480
WIRE 624 512 624 480
WIRE 240 624 240 592
WIRE 624 624 624 592
FLAG -288 192 0
FLAG -416 -208 0
FLAG 240 624 0
FLAG 720 -208 out1
FLAG 624 624 0
FLAG 1056 192 0
FLAG 1056 -112 0
FLAG 432 432 0
SYMBOL npn 80 144 R0
SYMATTR InstName Q1
SYMATTR Value BFR92A
SYMBOL npn 400 144 M0
SYMATTR InstName Q2
SYMATTR Value BFR92A
SYMBOL res 704 -368 R0
SYMATTR InstName R2
SYMATTR Value 500
SYMBOL res 128 352 R0
SYMATTR InstName R3
SYMATTR Value 1200
SYMBOL voltage -416 -368 R0
SYMATTR InstName V1
SYMATTR Value 10V
SYMBOL voltage 240 608 R180
WINDOW 0 24 96 Left 2
WINDOW 3 24 16 Left 2
SYMATTR InstName V2
SYMATTR Value 5V
SYMBOL voltage -160 192 R90
WINDOW 3 24 152 Left 2
WINDOW 123 24 124 Left 2
WINDOW 39 0 0 Left 2
SYMATTR Value PULSE(-1m 1m 0 100p 100p 1n 2n)
SYMATTR Value2 AC 1
SYMATTR InstName V3
SYMBOL res 0 176 R90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R4
SYMATTR Value 50
SYMBOL res 912 176 R90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R5
SYMATTR Value 50
SYMBOL voltage 624 608 R180
WINDOW 0 24 96 Left 2
WINDOW 3 24 16 Left 2
SYMATTR InstName V4
SYMATTR Value 5V
SYMBOL npn 784 -160 M0
SYMATTR InstName Q3
SYMATTR Value BFR92A
SYMBOL voltage 928 -112 R270
WINDOW 0 32 56 VTop 2
WINDOW 3 -32 56 VBottom 2
WINDOW 123 0 0 Left 2
WINDOW 39 0 0 Left 2
SYMATTR InstName V6
SYMATTR Value 3
SYMBOL npn 208 -160 M0
SYMATTR InstName Q6
SYMATTR Value BFR92A
SYMBOL res 416 288 R0
SYMATTR InstName R8
SYMATTR Value {rb}
SYMBOL res 912 -128 R90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R9
SYMATTR Value 100
SYMBOL res 128 -368 R0
SYMATTR InstName R1
SYMATTR Value 500
SYMBOL npn 784 144 M0
SYMATTR InstName Q4
SYMATTR Value BFR92A
SYMBOL npn 464 144 R0
SYMATTR InstName Q5
SYMATTR Value BFR92A
SYMBOL res 320 352 R0
SYMATTR InstName R7
SYMATTR Value 1200
SYMBOL res 512 352 R0
SYMATTR InstName R6
SYMATTR Value 1200
SYMBOL res 704 352 R0
SYMATTR InstName R10
SYMATTR Value 1200
SYMBOL res 272 256 R90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R11
SYMATTR Value 240
SYMBOL res 656 256 R90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R12
SYMATTR Value 240
SYMBOL cap 304 320 R90
WINDOW 0 0 32 VBottom 2
WINDOW 3 32 32 VTop 2
SYMATTR InstName C1
SYMATTR Value 900f
SYMBOL cap 688 320 R90
WINDOW 0 0 32 VBottom 2
WINDOW 3 32 32 VTop 2
SYMATTR InstName C2
SYMATTR Value 900f
SYMBOL voltage 1040 192 R90
WINDOW 3 24 152 Left 2
WINDOW 123 24 124 Left 2
WINDOW 39 0 0 Left 2
SYMATTR Value PULSE(-1m 1m 0 100p 100p 1n 2n)
SYMATTR Value2 AC 1
SYMATTR InstName V5
TEXT 16 -520 Left 2 !;tran 5u
TEXT 8 -464 Left 2 !.ac dec 100 1k 4G
TEXT 336 -520 Left 2 !.param rb=50
TEXT 328 -464 Left 2 !;.step param rb list 5 50 500 5k