Electronics Forum -> Dc Level On Output Of Sine Generator?

Electronics Forum

Help

Members

Calendar

Welcome Guest ( Log In | Register )

Resend Validation Email

Electronics Forum -> Analog Electronics -> General Analog Electronics

Forum Rules (Please read before posting)

Dc Level On Output Of Sine Generator?, Capacitive coupling not working?

Topic Options

treez

Posted: January 18, 2013 02:44 pm

Forum Addict

Group: Trusted Members
Posts: 897
Member No.: 17,791
Joined: August 29, 2008

Thanks, how about the problem i am having here with a DC level appearing in the sine wave output of a filtered square wave circuit?.........................

I have produced a 50KHz sine wave by filtering a 5V, -5V square wave in LTspice.

Despite the output being capacitively coupled, the output sine wave has managed to acquire a DC level of 70mV…….the input square wave has an input DC level of 0mV.

How has the sine wave got this DC level?…here is the schematic….(its also attached )

Schematic
http://i49.tinypic.com/2953lom.jpg

Here is the output sine waveform, showing its been “Lifted”….

Output waveform
http://i45.tinypic.com/wi4ag.jpg

Here is the LT1006 op amp datasheet:
http://cds.linear.com/docs/Datasheet/1006fa.pdf

Simulation file:

CODE

Version 4
SHEET 1 1624 680
WIRE -128 -144 -128 -176
WIRE -16 -144 -16 -176
WIRE 1552 -144 1424 -144
WIRE 1136 -112 1104 -112
WIRE 1232 -112 1216 -112
WIRE 672 -96 640 -96
WIRE 768 -96 752 -96
WIRE 208 -80 176 -80
WIRE 304 -80 288 -80
WIRE -128 -32 -128 -64
WIRE -16 -32 -16 -64
WIRE 1504 -16 1504 -48
WIRE 1168 0 1168 -32
WIRE 1424 0 1424 -144
WIRE 1472 0 1424 0
WIRE 704 16 704 -16
WIRE 1104 16 1104 -112
WIRE 1136 16 1104 16
WIRE 1552 16 1552 -144
WIRE 1552 16 1536 16
WIRE 1600 16 1600 0
WIRE 1600 16 1552 16
WIRE 240 32 240 0
WIRE 640 32 640 -96
WIRE 672 32 640 32
WIRE 1232 32 1232 -112
WIRE 1232 32 1200 32
WIRE 1248 32 1232 32
WIRE 1344 32 1312 32
WIRE 1472 32 1344 32
WIRE 176 48 176 -80
WIRE 208 48 176 48
WIRE 768 48 768 -96
WIRE 768 48 736 48
WIRE 832 48 768 48
WIRE 928 48 896 48
WIRE 1024 48 1008 48
WIRE 1136 48 1024 48
WIRE 304 64 304 -80
WIRE 304 64 272 64
WIRE 352 64 304 64
WIRE 448 64 416 64
WIRE 560 64 528 64
WIRE 672 64 560 64
WIRE 1344 64 1344 32
WIRE 0 80 -80 80
WIRE 96 80 80 80
WIRE 208 80 96 80
WIRE 1024 96 1024 48
WIRE 560 112 560 64
WIRE 1104 112 1104 16
WIRE 1504 112 1504 48
WIRE -80 128 -80 80
WIRE 96 128 96 80
WIRE 640 128 640 32
WIRE 1168 128 1168 64
WIRE 176 144 176 48
WIRE 240 144 240 96
WIRE 704 144 704 80
WIRE 1024 256 1024 160
WIRE 1104 256 1104 192
WIRE 1344 256 1344 144
WIRE 560 272 560 176
WIRE 640 272 640 208
WIRE -80 288 -80 208
WIRE 96 288 96 192
WIRE 176 288 176 224
FLAG -16 -32 0
FLAG -128 -32 0
FLAG -16 -176 5V
FLAG -128 -176 -5V
FLAG 240 0 5V
FLAG 240 144 -5V
FLAG 176 288 0
FLAG -80 288 0
FLAG 96 288 0
FLAG 704 -16 5V
FLAG 704 144 -5V
FLAG 640 272 0
FLAG 560 272 0
FLAG 1168 -32 5V
FLAG 1168 128 -5V
FLAG 1104 256 0
FLAG 1024 256 0
FLAG 1344 256 0
FLAG 1504 -48 5V
FLAG 1504 112 -5V
FLAG 1600 0 OUT
SYMBOL voltage -80 112 R0
WINDOW 123 0 0 Left 2
WINDOW 39 24 110 Left 2
SYMATTR InstName V1
SYMATTR Value PULSE(-5 5 0 10n 10n 10u 20u)
SYMATTR SpiceLine Rser=0.01
SYMBOL Opamps\\LT1006 240 0 R0
SYMATTR InstName U1
SYMBOL res 96 64 R90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R1
SYMATTR Value 10k
SYMBOL cap 80 128 R0
SYMATTR InstName C1
SYMATTR Value 1n
SYMATTR SpiceLine Rser=0.01
SYMBOL voltage -16 -160 R0
WINDOW 123 0 0 Left 2
WINDOW 39 24 30 Left 2
SYMATTR InstName V2
SYMATTR Value 5
SYMATTR SpiceLine Rser=0.01
SYMBOL voltage -128 -160 R0
WINDOW 123 0 0 Left 2
WINDOW 39 24 30 Left 2
SYMATTR InstName V3
SYMATTR Value -5
SYMATTR SpiceLine Rser=0.01
SYMBOL res 304 -96 R90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R2
SYMATTR Value 10k
SYMBOL res 192 240 R180
WINDOW 0 36 76 Left 2
WINDOW 3 36 40 Left 2
SYMATTR InstName R3
SYMATTR Value 10k
SYMBOL Opamps\\LT1006 704 -16 R0
SYMATTR InstName U2
SYMBOL res 544 48 R90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R5
SYMATTR Value 10k
SYMBOL cap 544 112 R0
SYMATTR InstName C3
SYMATTR Value 1n
SYMATTR SpiceLine Rser=0.01
SYMBOL res 768 -112 R90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R6
SYMATTR Value 10k
SYMBOL res 656 224 R180
WINDOW 0 36 76 Left 2
WINDOW 3 36 40 Left 2
SYMATTR InstName R7
SYMATTR Value 10k
SYMBOL Opamps\\LT1006 1168 -32 R0
SYMATTR InstName U3
SYMBOL res 1024 32 R90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R4
SYMATTR Value 10k
SYMBOL cap 1008 96 R0
SYMATTR InstName C2
SYMATTR Value 1n
SYMATTR SpiceLine Rser=0.01
SYMBOL res 1232 -128 R90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R8
SYMATTR Value 10k
SYMBOL res 1120 208 R180
WINDOW 0 36 76 Left 2
WINDOW 3 36 40 Left 2
SYMATTR InstName R9
SYMATTR Value 5k1
SYMBOL cap 416 48 R90
WINDOW 0 0 32 VBottom 2
WINDOW 3 32 32 VTop 2
SYMATTR InstName C4
SYMATTR Value 10µ
SYMATTR SpiceLine Rser=0.01
SYMBOL cap 896 32 R90
WINDOW 0 0 32 VBottom 2
WINDOW 3 32 32 VTop 2
SYMATTR InstName C5
SYMATTR Value 10µ
SYMATTR SpiceLine Rser=0.01
SYMBOL cap 1312 16 R90
WINDOW 0 0 32 VBottom 2
WINDOW 3 32 32 VTop 2
SYMATTR InstName C6
SYMATTR Value 10µ
SYMATTR SpiceLine Rser=0.01
SYMBOL res 1328 48 R0
SYMATTR InstName R10
SYMATTR Value 100K
SYMBOL Opamps\\LT1006 1504 -48 R0
SYMATTR InstName U4
TEXT 702 304 Left 2 !.tran 0 1000m 0 startup

Sch3mat1c	Posted: January 18, 2013 06:08 pm
Forum Addict ++ Group: Moderators Posts: 18,142 Member No.: 73 Joined: July 24, 2002	You forgot to bias the +input pins. Try a 100k resistor to GND. Tim -------------------- Answering questions is a tricky subject to practice. Not due to the difficulty of formulating or locating answers, but due to the human inability of asking the right questions; a skill that, were one to possess, would put them in the "answering" category.

Gorgon	Posted: January 19, 2013 12:44 pm
Forum Addict ++ Group: Trusted Members Posts: 2,927 Member No.: 3,861 Joined: December 18, 2005	The input range is not rail-to-rail, it only goes to the negative rail and 1.5V from the positive rail (just a fast peep at the datasheet). This mean you'll have an 'clipping' of the signal, and the feedback, on the positive side and this will come out as an averaging offset on the signal. To remove this you'll either need to increase the supply voltage, or reduce the input signal range. -------------------- Light travels faster than sound. That's why some people appear bright until they speak!

1 User(s) are reading this topic (1 Guests and 0 Anonymous Users)

0 Members:

« Next Oldest | General Analog Electronics | Next Newest »

:: support us ::

ElectronicsSkin by DutchDork & The-Force