+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.

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

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,

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.

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.

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

Best regards, Spehro Pefhany

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

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

Jamie

Or golden ones.

s.

CD4051, CD4052, CD4053

gikey.)

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

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.

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,

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.

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.

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

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.

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

The Supertex is your ticket. Plenty of selection.