+1/-1 gain stage

Being a cheapskate I usually just use an emitter follower with another resistor in the collector, of equal value as the emitter resistor. Or same with a FET if they have to be 100% equal. Provided there is no need for good DC stability.

--
Regards, Joerg 

http://www.analogconsultants.com/

Oh, that's in AoE isn't it? Nothing wrong with cheap as long as it works.

And yeah, DC stability is not needed. Hmm, I'll still need to switch the two outputs onto the same line... into a low pass, it's a home-brew lockin thing.

George H.

Don't know if in there but I imagine it would be.

Bingo!

That's what they made these for:

They also come in 8:1, 4:2, chocolate, vanilla and other flavors. And in

15V versions (CD-series) should that be needed. Even higher voltage muxes are available from Supertex but those cost more than a few nickels.

--
Regards, Joerg 

http://www.analogconsultants.com/

Slaps head, Dang I was asking a co-worker if we had any analog switches. He couldn't remember. But I have loads of CD4066's (15 volts) on the shelf.

Do any of those go to 30V? That would be nice (Don't worry I'll check digikey.) I've got plenty of nickels :^)

George H.

The problem is, different op amp branches have different phase shifts and gains, and symmetry suffers

Yep, that's the classic phase splitter, two copies of the signal with opposite polarity; transistors are well-behaved for this. DC levels and power supply noise are the main issues here (and op amps also aren't great at power rejection when F gets large).

I'd prefer the center-tapped transformer, alternately grounding one or the other leg and taking output from the tap. It has symmetry and NO real phase error; either build one, or buy a Mini-Circuits mixer (comes with diode switches already in place).

If you're starting with 74HC74 style logic drive for this,

74(HC,AC,whatever)125 makes a pretty good analog-switch-to-ground, and the spare '74 outputs and spare 74HC125 sections can be employed to null the logic feedthrough. It's a single power supply solution.

Those last two don't have an error from the switch resistance.

There are some fast CMOS analog switches around. Or use a phemt.

Maybe a Gilbert cell, or one of those fancy new active mixers, if you want to go fast.

--

John Larkin         Highland Technology, Inc 

jlarkin att highlandtechnology dott com 
http://www.highlandtechnology.com

The killer is charge injection, and especially its change vs signal voltage. Charge injection into time-varying resistors makes DC voltages, and charge spikes can also confuse upstream/downstream opamps.

--

John Larkin         Highland Technology, Inc 

jlarkin att highlandtechnology dott com 
http://www.highlandtechnology.com

SA602A gives you a mixer with ~18dB of gain.

Best regards, Spehro Pefhany

--
"it's the network..."                          "The Journey is the reward" 
speff@interlog.com             Info for manufacturers: http://www.trexon.com 
Embedded software/hardware/analog  Info for designers:  http://www.speff.com

The other way to do a lockin is to digitize and do the phase detection digitally. That avoids a bunch of analog problems.

--

John Larkin         Highland Technology, Inc 

jlarkin att highlandtechnology dott com 
http://www.highlandtechnology.com

I don't think Digikey takes wooden one's!

Jamie

Or golden ones.

--

John Larkin         Highland Technology, Inc 

jlarkin att highlandtechnology dott com 
http://www.highlandtechnology.com

n

s.

CD4051, CD4052, CD4053

gikey.)

x.html

Analog has lots of stuff that handles +/-15V rails (as well as lots of lowe r voltage stuff).

I think the original inventor for the higher-voltage analog switches was Si liconix, which is now Intersil

age-switches

Sadly, they don't seem to do much better - nothing over a 34V single supply voltage. Maxim probably claims to sell similar parts, if you are prepared to buy enough of them.

Supertex does better, as has been pointed out.

I haven't looked at their stuff in recent years - my favourite broad-line s upplier is Farnell/element 14/Newark - and they don't seem to stock Superte x parts. Arrow and Avnet both stock their stuff in Australia, so I could ge t Supetex parts if I needed them, which is comforting. I've not often neede d Supertex parts, but when I have needed them second-sourcing has been a pr oblem.

--
Bill Sloman, Sydney

Grin, yeah most of those are $h!t! I scribbled a new circuit, but no camera here :( .-R2---. | |\ | Vin---+---R1--+-|-\ | | | >-+-Vout +--R3--+--|+/ R4 |/ | GND The action is all in R4 R1,2,3 are all about 10k.. exact values picked to make the gains, come out right.

So first R4 is a ~1k resistor, that connects to the top of the switch. This takes the exact value of the switch resistance out of the equation... mosty. And then I'm thinking the switch should have a ~100k resistor in parallel. (maybe less?) That is to keep the voltage across the switch down. Or can I just leave it hanging there?

I'm a low speed kinda guy,

10MHz is plenty fast enough.. well for now.

George H.

Excellent! I was thinking I could copy your other post about the switched center tapped transformer solution.

What switch impedance does the transformer want? I don't know much about transformers, which makes me lean towards an opamp.

As far as the flip-flop quadrature drive. I'm punting at the moment and using my rigol DDS.

George H.

OK, that sounds like capacitance.. in the switch and stray. Re: changing capacitance with signal level... Wow... I'm having this very love, hate relationship with capacitance. Maybe capacitance is female? Resistance is much more male and predictable. (though it only dissipates things in the end.)

George H.

10 MHz is nontrivial for analog switching and particularly for an accurate lockin. CD40xx type switches won't switch in 50 ns. HC40xx types would be mediocre.

I'd look at some of the new RF active mixers, ADI and LTC maybe.

And a phemt might be good, as a low-voltage switch to ground.

--

John Larkin                  Highland Technology Inc 
www.highlandtechnology.com   jlarkin at highlandtechnology dot com    

Precision electronic instrumentation

Yowzer! it even comes in a pdip!

Is there a freq. min. on that? I'm thinking that's way above me. (frequency-wise) Maybe CV measurements from

10kHz-1MHz (10MHz)... (but I get to change the limits if it gets too hard.) And something everyone can see on their 'scope.

George H.

Well, that's what men do, dissipating things. Cigars, booze, gambling, they crash sports cars, wreck motor cycles. I just dissipated the main pivot bearing on my new (!) mountain bike.

--
Regards, Joerg 

http://www.analogconsultants.com/

If +/-7.5V or +15V is enough that would work.

The Supertex is your ticket. Plenty of selection.

--
Regards, Joerg 

http://www.analogconsultants.com/