A capacitor will charge at a linear rate if it is charged by a constant current. Typically, that is how a sweep (sawtooth) generator is designed. For a low frequency illustration put a capacitor in the feed back loop of an op amp (Bipolar config.) and apply a voltage to the inv input through a resistor and watch the liner slope on a scope. It will be inverted from the polarity of the input voltage because the R is in the inv input. Of course non-inv in is grounded. Discharge the cap and it will start again. Polyester or polypropylene caps have a low leakage. Best for this type of application. So, you can design a constant current charge discharge at such a frequency without too much difficulty. 5 MHz is not fast. If you like, you can talk to me off-list about it and I can try to help you. My hours are often unpredictable. Regards Rich ----- Original Message ----- From: "Edward Cooper" To: "Microcontroller discussion list - Public." Sent: Monday, June 05, 2006 1:51 PM Subject: [EE] High Frequency Sawtooth generator > Hi all > > Anyone got any suggestions as to how to put together a 5MHz sawtooth > generator, I'd really like something quite linear and adjustable if > possible, can't see any simple chip solutions out there so looking > for a bit of advice. > > Its for playing with a FMCW radar module if anyone is interested > > Cheers > > Ed > -- > http://www.piclist.com PIC/SX FAQ & list archive > View/change your membership options at > http://mailman.mit.edu/mailman/listinfo/piclist -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist