Question on sweeping Exar's XR2206 function generator chip

[stuart ferguson]

Hi...

Question on sweeping Exar's XR2206 function generator chip

I am having problems getting the XR2206 to sweep with a ramp voltage.
I have the XR2206 configured as per fig10. in the datasheet, and I
want to sweep from around 975kHz to 1025kHz. ( centre frequency 1MHz).

I am sweeping with ramp signal at 33Hz, +/- 2 volts centred on zero,
but when i apply the ramp voltage to resistor at pin 7, the ramp is
offset by about 1 volt and is distorted. Is this normal? I am only
getting a couple of MHz of sweep, way lower than my goal...

What am I doing wrong? Any ideas

 

[John Popelish]

Hi...

Question on sweeping Exar's XR2206 function generator chip

I am having problems getting the XR2206 to sweep with a ramp voltage.
I have the XR2206 configured as per fig10. in the datasheet, and I
want to sweep from around 975kHz to 1025kHz. ( centre frequency 1MHz).

I am sweeping with ramp signal at 33Hz, +/- 2 volts centred on zero,
but when i apply the ramp voltage to resistor at pin 7, the ramp is
offset by about 1 volt and is distorted. Is this normal? I am only
getting a couple of MHz of sweep, way lower than my goal...

What am I doing wrong? Any ideas

The voltage at pin 7 is held, internally at about 3 volts relative to
pin 12. The current that passes out of this pin to a more negative
sink sets the frequency. When you say the ramp voltage is offset, are
you talking about the voltage on pin 7 or on the far end of the
resistor you have connected to pin 7?

Figure 10 on the data sheet suggests how a control voltage can be
connected to sweep frequency:
http://ems.calumet.purdue.edu/shop/Data Sheets/IC/xr2206.pdf

There are other ways to convert a voltage to a current and connect
that current to pin 7, also.