variable voltage output

Steve,

There are a couple approaches here. First, to meet the slew rate requirement you will need a current feedback amplifier and the gain can be controlled by a PGA. For a differential signal, you could use the PGA870 with a variable gain up to 20dB and 0.5dB steps followed by THS6204. For a single ended signal, you could use a DAC to drive the VCA824 control pin followed by the THS3091. What is the application here? Also, is the 24V going to be used as a single or split supply?

Thanks,

Luke Lapointe

High Speed Amplifier Applications

Luke Lapointe said:

Steve,

There are a couple approaches here. First, to meet the slew rate requirement you will need a current feedback amplifier and the gain can be controlled by a PGA. For a differential signal, you could use the PGA870 with a variable gain up to 20dB and 0.5dB steps followed by THS6204. For a single ended signal, you could use a DAC to drive the VCA824 control pin followed by the THS3091. What is the application here? Also, is the 24V going to be used as a single or split supply?

Thanks,

Luke Lapointe

High Speed Amplifier Applications

Thanks - this will be used with a single ended 24V supply

we want to output a monotonic frequency or single pulses of variable width.... with amplitudes from 3V to 20V. this is for a tester 

any appnotes exist using the parts you mention?

Steve,

I have attached a TINA schematic demonstrating how you would implement the single ended approach with the VCA824 and THS3091. Using a 10V single ended supply for the VCA824 with 5V common mode, the VG pin would give the max amplitude at 1V above common mode and minimum at 1V below common mode. This would then drive the THS3091 operating on a 24V single supply with an output swing of 3V to 20V and 100MHz bandwidth. If you need to change the common mode voltage, you can AC couple the signal and rebias it externally.

 5305.VCA824_THS3091_Single_Ended_Generation.TSC

The VG pin could be digitally controlled by the TLC7524 DAC followed by TL074 buffer.

Please let me know if this answered your question.

Thanks,

Luke Lapointe

High Speed Amplifier Applications

Luke,

thanks, is TINA freeware?

Steve,

Yes, you can download the latest version of TINA here: http://www.ti.com/tool/tina-ti#buy

Regards,

Luke Lapointe

High Speed Amplifier Applications

Luke,

I am looking at the output of the THS3091 (as implemented in the design you sent me)

the rise time (from 0 to 8V) is excellent - less than 10ns, but the falling edge is ~32ns . is there a way to make it symetrical? ...ideally Tr and Tf of ~10ns. I have the output connected to a 220ohm load

is this a limitation of current feedback amps or is there an op amp with a more symetrical output?

Thanks in advance - your support has been great

SR 

Steve,

It sounds like one of the input/output stages is saturating. If you upload your schematic, I will take a look.

Thanks,
Luke

By the way:

In TINA, there is an Function Generator available. However, if I use ARB-Signals, the signals come only one time (single shot). How can I get periodically arbitrary signals?

Best regards

Franz Peter

Hi Franz,

You can make a piecewise linear waveform in TINA-TI which is either repetitive or single-shot.

Here is an image which shows you how to make it repetitive:

Here is an entire Analog Wire post which discusses more options:

What you always wanted to know about TINA-TI but were afraid to ask! (Part 4)

Other Parts Discussed in Post: TINA-TI , LMH6554 This installment of the TINA-TI series is based on your requests from the list in Part 1 . In this post we’ll learn how to generate: Time varying…

By Hooman Hashemi over 11 years ago in Technical articles > Analog

Regards,

Hooman

Hi Steve,

One way you can do that would be to use the LMH6523 Variable Gain Amplifier (digital control) to control your square wave amplitude. Then, you could process your amplitude controlled square wave (at LMH6523 output) through a VCVS (voltage controlled voltage source where you set its gain) to generate the maximum swing you are asking for (20V) since the LMH6523 would not be able to swing that much.

In this example, I'm producing up to 600V at "V_amplified" and I'm controlling the swing by making VB2 (digital input attention control of the LMH6523) a controlled object toggling between 0 and 1.

Here is the TINA-TI file for the above:

LMH6523 Variable Square Wave E2E Hooman 10_30_15.TSC

Double click the output VCVS3, "Operation Mode" to change its gain (currently set to 200 V/V).

Regards,

Hooman