AD633 squaring/single power supply issue

[Atlas5]

Hello,

I am trying to preform the squaring of a sin wave using a AD633 multiplier using OrCAD. So far, I am following the method that the datasheet produces for squaring the input. The only difference is that I am trying to use a single power supply instead of two seperate ones. Can anyone give me advice on how I can change the curcuit so that I can get the right output.

Also, attached is my simplified circuit which shows the multiplier on top and the power function (simulation). The current result picture shows the result I am getting if using the multiplier. The last picture shows the result I get by using the power function in OrCAD. Let me know if you need more information.

Thanks.

 

[ericgibbs]

hi,
Normally pin 5 is connected the -V supply. your diagram shows it 'floating', try connecting pin 5 to 0V.

I suspect it will not work to specification as its designed for dual supply operation.

 

[Atlas5]

hi,
Normally pin 5 is connected the -V supply. your diagram shows it 'floating', try connecting pin 5 to 0V.

I suspect it will not work to specification as its designed for dual supply operation.

Thank you for the reply.

At the moment pin 5 is connected to ground with a 0.1uF cap to help regulate it.

As of working for speculations, I was just wondering if there is a way to make it work so that it can use a single power supply instead of a dual one.

 

[crutschow]

At the moment pin 5 is connected to ground with a 0.1uF cap to help regulate it.

As of working for speculations, I was just wondering if there is a way to make it work so that it can use a single power supply instead of a dual one.

A capacitor does not regulate, it filters. You need a connection to ground to carry the IC operating current. Capacitors provide a block to DC.

The operating input and output range of the AD633 is within 3V to 4V of either supply voltage (see Fig. 6 in the data sheet). Thus for operation on a single supply, the input and output voltages can go no lower than 3-4V above ground or no higher then 3-4V below the supply voltage. If you can maintain the input and output signals within that range, then it should work with a single supply, although at lower voltages, the accuracy may suffer. It will obviously not work properly down to ground with a single supply.

 

[Atlas5]

Thank you for your reply.

A capacitor does not regulate, it filters. You need a connection to ground to carry the IC operating current. Capacitors provide a block to DC.

You are correct it does filter as filter would be the better word for this.

The operating input and output range of the AD633 is within 3V to 4V of either supply voltage (see Fig. 6 in the data sheet). Thus for operation on a single supply, the input and output voltages can go no lower than 3-4V above ground or no higher then 3-4V below the supply voltage. If you can maintain the input and output signals within that range, then it should work with a single supply, although at lower voltages, the accuracy may suffer. It will obviously not work properly down to ground with a single supply.

Hmmm. I see then. If that is the case then would my application work better if I use the adl5391 multiplier instead since I can connect it to ground and use a single power supply of 5V.

 

[crutschow]

Hmmm. I see then. If that is the case then would my application work better if I use the adl5391 multiplier instead since I can connect it to ground and use a single power supply of 5V.

Yes, that would appear to be a better device for single supply operation it the accuracy meets your requirements.

 

[Atlas5]

Yes, that would appear to be a better device for single supply operation it the accuracy meets your requirements.

Alright. I was wondering if you would know where I could find a PSPICE model of the part since I cannot seem to find it online.

 

[crutschow]

Since Analog Devices does not offer a spice model for the adl5391, I suspect there is none available.

 

[Atlas5]

Since Analog Devices does not offer a spice model for the adl5391, I suspect there is none available.

If that is the case then are there any alternatives since I would like to simulate the multiplier so that I can confirm that it works.

 

[crutschow]

Don't know of any off hand. You need to search the multiplier vendors to see if they have a part you can use that also has a Spice model available.

 

[Atlas5]

That hasnt been an easy task since I have spending a good amount of time trying to find one but I had no luck so far.

 

[Atlas5]

After some more searching I think I will have to go and use the dual power supply for the AD633. The only difference is that I will use another chip called MAX868 which is a Regulated, Adjustable -2x Inverting Charge Pump. From my understanding I can use this chip to invert a positive power supply and invert it to a negative power supply but doubled. In this regard I would have to use a voltage divider to bring the voltage back down to -5V since that is where I would need it. Anyway, let me know if this could work too or if you have any other suggestions.

Here is the link to the chip's datasheet.
https://www.electro-tech-online.com/custompdfs/2012/05/MAX868.pdf

 

[crutschow]

After some more searching I think I will have to go and use the dual power supply for the AD633. The only difference is that I will use another chip called MAX868 which is a Regulated, Adjustable -2x Inverting Charge Pump. From my understanding I can use this chip to invert a positive power supply and invert it to a negative power supply but doubled. In this regard I would have to use a voltage divider to bring the voltage back down to -5V since that is where I would need it. Anyway, let me know if this could work too or if you have any other suggestions.

The "voltage divider" you need is used to regulate the output voltage as shown in Figure 4 of the data sheet. For R1 = R2 and adding the dotted line connection, the output voltage will be the negative of the input voltage.

 

[Atlas5]

Ah I see. I will try that out then and see how that will work in my application. If there are any other suggestions on getting a negative power supply through a positive power supply or another method as a "more affordable" solution to my issue then I would love to hear it.

Thanks.