Freq. Independent Phase Shifter
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From: Bill Murphy on 9 May 2010 17:33 I am using a commercial stereo amp to output continuous wave test signals in the low audio range, up to about 2KHz. However, I need a third channel with a 120 degree phase shift. Is there a circuit that will do this evenly across this entire frequency range? Is it possible to do same using an off-the-shelf transformer and current subtraction? Any advice would be appreciated. Bill Murphy
From: Jim Thompson on 9 May 2010 17:46 On Sun, 09 May 2010 21:33:02 GMT, billmurphy(a)protech.com (Bill Murphy) wrote: >I am using a commercial stereo amp to output continuous wave test >signals in the low audio range, up to about 2KHz. However, I need a >third channel with a 120 degree phase shift. Is there a circuit that >will do this evenly across this entire frequency range? > >Is it possible to do same using an off-the-shelf transformer and >current subtraction? > >Any advice would be appreciated. > >Bill Murphy If you mean un-tweaked, you need to read up on Sidney Darlington's works. Otherwise a hand-adjusted all-pass will work, change frequency, tweak a pot to get 120�... did this with smear camera motor drivers when I was a student at MIT more than 50 years ago. ...Jim Thompson -- | James E.Thompson, CTO | mens | | Analog Innovations, Inc. | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | Phoenix, Arizona 85048 Skype: Contacts Only | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at http://www.analog-innovations.com | 1962 | The only thing bipartisan in this country is hypocrisy
From: Bill Sloman on 9 May 2010 18:14 On May 9, 11:33 pm, billmur...(a)protech.com (Bill Murphy) wrote: > I am using a commercial stereo amp to output continuous wave test > signals in the low audio range, up to about 2KHz. However, I need a > third channel with a 120 degree phase shift. Is there a circuit that > will do this evenly across this entire frequency range? > > Is it possible to do same using an off-the-shelf transformer and > current subtraction? > > Any advice would be appreciated. Check out Horowitz and Hill's "The art of Electronics". Section 5.16 talks about phase-sequence filters, which give a constant 90 degree shift over a range of frequencies. They consist of strings of equal value resistors with cross-connected capacitors whose values decrease in constant proportion per stage, halving in the example given, which isn't all that practical to set up. The bottom line is that it isn't trivial, and if you need to ask, you probably don't know enough to put together a circuit that will work. -- Bill Sloman, Nijmegen
From: John Larkin on 9 May 2010 18:59 On Sun, 09 May 2010 21:33:02 GMT, billmurphy(a)protech.com (Bill Murphy) wrote: >I am using a commercial stereo amp to output continuous wave test >signals in the low audio range, up to about 2KHz. However, I need a >third channel with a 120 degree phase shift. Is there a circuit that >will do this evenly across this entire frequency range? > >Is it possible to do same using an off-the-shelf transformer and >current subtraction? > >Any advice would be appreciated. > >Bill Murphy A transformer won't do it. Williams' filter book has some nice opamp-based allpass networks that will give you 90 deg phase shift over a wide range. A little adding-subtracting can get you to 120 from there. Often it's easier to generate signals with phase shifts than to start with a sine and shift it. I could sell you one of these... http://www.highlandtechnology.com/DSS/T340DS.html or better yet one of these... http://www.highlandtechnology.com/DSS/T346DS.html John
From: Winston on 9 May 2010 19:04
On 5/9/2010 2:33 PM, Bill Murphy wrote: > I am using a commercial stereo amp to output continuous wave test > signals in the low audio range, up to about 2KHz. However, I need a > third channel with a 120 degree phase shift. Is there a circuit that > will do this evenly across this entire frequency range? > > Is it possible to do same using an off-the-shelf transformer and > current subtraction? > > Any advice would be appreciated. > > Bill Murphy I would approach this using DDS (Direct Digital Synthesis). http://www.fpga4fun.com/DDS2.html A binary counter generates an address for two different memory devices. The devices are programmed with a binary sine wave. The second device is exactly like the first except the data are displaced an equivalent of 120 degrees in the address space. Each data stream drives a separate DAC. The output of the second DAC is filtered and amplified to drive your 3rd amplifier which has exactly the same phase characteristics as your first two amplifiers. Vary the clock speed into the binary counter to vary the output frequency. --Winston -- I'm already sending extortion money to my state's "Employment Development Department" but I would like to support *nationwide* organized crime directly, particularly for shakedowns of the elderly, subversion of the Democratic process through graft and corruption and perhaps the manufacture and distribution of illegal narcotics. What is the best way to increase money flow to the Mafia? Should I double my monthly payment to EDD or can I simply send checks to the "TRS Recovery" division of "FirstData Corporation"? Does the Mob have a website that accepts Paypal payments? |