Passive tri to sine converter

[Jim Thomas]

In terms of a working circuit, what is my best bet for simulating a
sinewave from a triangle input using only passive components?

IOW no transistors or op amps.

Supply is 9V single rail. Voltage in is 5V. Frequency is lower audio
range.

Thanks very much for any suggestions.

Jim Thomas

 

[[email protected]]

In terms of a working circuit, what is my best bet for simulating a
sinewave from a triangle input using only passive components?

IOW no transistors or op amps.

Supply is 9V single rail. Voltage in is 5V. Frequency is lower audio
range.

Thanks very much for any suggestions.

Jim Thomas

low pass CR network

 

[Pooh Bear]

In terms of a working circuit, what is my best bet for simulating a
sinewave from a triangle input using only passive components?

IOW no transistors or op amps.

Supply is 9V single rail. Voltage in is 5V. Frequency is lower audio
range.

Thanks very much for any suggestions.

I recall that Intersil ? made a function generator chip that used a
'diode ladder' arrangement to bend that triangle into a sine.

Graham

 

[John Larkin]

low pass CR network

RLC lowpass, or tuned LC bandpass, even better.

Unless you consider diodes to be "passive."

John

 

[John Fields]

In terms of a working circuit, what is my best bet for simulating a
sinewave from a triangle input using only passive components?

IOW no transistors or op amps.

Supply is 9V single rail. Voltage in is 5V. Frequency is lower audio
range.

---
For a single frequency around 100Hz, try this:


IN>------+
|
[13µF]
|
[100µH]
|
+----->OUT
|
[10R]
|
GND>-----+----->GND

Here's the circuit file for Linear's SwitcherCAD:

Version 4
SHEET 1 880 680
WIRE -80 256 -80 112
WIRE -80 432 -80 336
WIRE 112 112 -80 112
WIRE 112 224 112 192
WIRE 112 320 112 288
WIRE 112 432 112 400
FLAG -80 432 0
FLAG 112 432 0
SYMBOL ind 96 96 R0
SYMATTR InstName L1
SYMATTR Value 100e-3
SYMBOL cap 96 224 R0
SYMATTR InstName C1
SYMATTR Value 12e-6
SYMBOL voltage -80 240 R0
WINDOW 3 24 104 Invisible 0
WINDOW 39 0 0 Left 0
SYMATTR Value PULSE(2 7 0 0.005 0.005 0 .01 100)
SYMATTR InstName V1
SYMATTR Value2 AC 1
SYMBOL res 96 304 R0
SYMATTR InstName R1
SYMATTR Value 10
TEXT -360 360 Left 0 !;ac oct 256 10 1000000
TEXT -362 506 Left 0 !.tran 1

 

[[email protected]]

In terms of a working circuit, what is my best bet for simulating a
sinewave from a triangle input using only passive components?

IOW no transistors or op amps.

Supply is 9V single rail. Voltage in is 5V. Frequency is lower audio
range.

Thanks very much for any suggestions.

Jim Thomas

LC is surely the way to go if its fixed frequency. One RC stage can not
give you sin, no matter what the R and C values.


NT

 

[Phil Hobbs]

LC is surely the way to go if its fixed frequency. One RC stage can not
give you sin, no matter what the R and C values.


NT

For the "lower audio" range, LCs are not highly practical. What's so
horrible about active devices?

The simple way to do this is to build a sine wave oscillator and lock it
to the tri wave, or (failing this) to build a highish-Q active filter.
If it absolutely has to have no battery, run a voltage doubler off the
tri wave and power the circuit that way.

Cheers,

Phil Hobbs

 

[Joseph2k]

I recall that Intersil ? made a function generator chip that used a
'diode ladder' arrangement to bend that triangle into a sine.

Graham

Damn straight. worked pretty well, THD < 0.5%. for a single cap was
tunable over 2 decades in frequency. was second sourced in its day too,
about 30 years ago. 8038? 8308? 8388? damn, it was 30+ years ago and my
memory not is perfect.

 

[[email protected]]

IN>------+
|
[13µF]
|
[100µH]
|
+----->OUT
|
[10R]
|
GND>-----+----->GND

John Fields
Professional Circuit Designer

John, shoudn't that be 200mH?
Dick

 

[[email protected]]

If diodes are allowed, set up a few diodes along a voltage divider to
progressively compress the triangle wave. HP did this with
considerable sucess in their 3300A function generator.

 

[Michael A. Terrell]

Damn straight. worked pretty well, THD < 0.5%. for a single cap was
tunable over 2 decades in frequency. was second sourced in its day too,
about 30 years ago. 8038? 8308? 8388? damn, it was 30+ years ago and my
memory not is perfect.

8038, and an updated version is availible from Maxim.

--
Service to my country? Been there, Done that, and I've got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida

 

[[email protected]]

I recall that Intersil ? made a function generator chip that used a
'diode ladder' arrangement to bend that triangle into a sine.

Graham

Exar made a sine-wave generator, the XR2206, that did this too. We
used to use them in modems.

Exar used the exponential I-V characteristic of a couple of diodes to
round ('clip') the 'points' off a triangle wave. For lowest
distortion, the input triangle amplitude must be carefully
adjusted/controlled. Exar's XR2206 datasheet related their technique
in splendid detail. Alas, I don't seem to have my copy (which is
rare--I don't usually lose things).

I've used LEDs as the diodes to get a higher voltage output.

Cheers,
James Arthur

 

[Pooh Bear]

Exar made a sine-wave generator, the XR2206, that did this too. We
used to use them in modems.

The Exar part might be an 'improved' version They did that quite often.

Exar used the exponential I-V characteristic of a couple of diodes to
round ('clip') the 'points' off a triangle wave. For lowest
distortion, the input triangle amplitude must be carefully
adjusted/controlled. Exar's XR2206 datasheet related their technique
in splendid detail. Alas, I don't seem to have my copy (which is
rare--I don't usually lose things).

It's still there.....
http://www.exar.com/product.php?ProdNumber=XR2206&areaID=7

Graham

 

[Rich Grise]

I recall that Intersil ? made a function generator chip that used a
'diode ladder' arrangement to bend that triangle into a sine.

http://www.intersil.com/data/FN/FN2864.pdf

Cheers!
Rich

 

[[email protected]]

The Exar part might be an 'improved' version They did that quite often.



It's still there.....
http://www.exar.com/product.php?ProdNumber=XR2206&areaID=7

Graham

Hey, thanks! I wasn't sure they still existed.

I don't have my *original* XR2206 datasheet, but I did find an old
app note. Their method was not exactly as I described -- I'd mixed it
up with another, related circuit.

Here's Exar's technique for converting triangle waves to sine waves:


..
.. Vcc >--+-------------+
.. | |
.. | .-.
.. | | |
.. | | | R.load
.. | '-'
.. | |
.. | o--------------> Sine wave
output
.. | |
.. |/ \|
.. /\ / >-------| Q1 Q2 |-----+
.. / \ / |>. .<| |
.. / \ / | +---+ | |
.. \ / | | V | |
.. \/ >---+ o--o-\/\/\----o |
.. | | Re | |
.. | | | |
.. Triangle wave | i1 | i1 | |
.. input | | | | | |
.. | | v | v |
.. | | | |
.. | === === |
.. | GND GND |
.. | |
.. | |
.. +---------------------------+

KEYWORDS: triangle to sinewave converter waveform waveshaping
logarithmic

Re is adjusted to bring Q1/Q2 close to cutoff at the input's peaks,
causing the transfer characteristics to become logarithmic there rather
than linear. Consequently, the triangle's peaks are rounded off, and a
low-distortion approximation of a sinewave at the output results. The
accompanying info indicates THD of 0.5% can be achieved with a single
adjustment.

Jim Williams reports a similar circuit he calls a 'logarithmic
shaper'. His version has two tweaks, an input-level adjustment he
calls 'wave-shape trim', and an input offset adjustment he calls
'symmetry adjust'. JW reports 0.35% THD.

Best Regards,
James Arthur

 

[Pooh Bear]

http://www.intersil.com/data/FN/FN2864.pdf

Cheers!
Rich

Excellent, and there's the sine conveter in all its glory.

Graham