How to get the maximum output voltage from the MAX2606 VCO

According to the datasheet of MAX2606, Absolute maximum rating for OUT+, OUT- to GND -0.3V to (Vcc+0.6V). And Vout (p-p) (differential) = 2x1mA[(1kΩxRload)/(1kΩ+Rload) I implemented the following circuit (both C2 and C3 are 2.2nF and other values are same as in the diagram) and get the single ended output and measured using the oscilloscope.

Unfortunately the output peak to peak voltage is just 300mV. (Vcc = 4.5V) :( Why I can"t get at output peak to peak voltage least up to 1/2Vcc ? Please help me, I want to input the output of this to a 74F14 schmmit trigger IC. Any suggestions please?

Absolute maximum ratings are what the chip will withstand without blowing up - it is not a performance statement. The chip will supply a maximum of -8dBm differential. I don't know what that is in V but it is a lot less than you want, I suspect (and even less if you use it single ended).

Keith

The easiest way is to add an amplifier. If you only need a TTL type output, use a Schmitt trigger or a TTL-output comparator. Squeezing more than a specified output often kills a good device.

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If you only need a narrow-band output, use a suitable transformer with its primary connected to OUT+ and OUT- via the capacitor shown, the secondary of it connected from GND to OUT. This way yo can get almost 2xVcc to a high-impedance load.

What do you mean by V? output voltage? It should be at least 2V (or more).
What should I use for the second load if I use differential mode? A resistor?


Yeah. I tried to add an transistor amplifier (2N2222) but since it's fT is around 250 MHz, I couldn't get a amplified voltage (@ 100 MHz and Vcc of the amplifer circuit is 5V) to input to 74F14 Schmitt trigger. However, I didn't try it for differential mode. I ordered a transistor with higher fT (9 GHz) and I have to wait until it delivered to me. probably until next week.
But I need a much quicker solution for this.

Can you explain more about this? If I changed the C2 or C3 capacitor values, can I see a better output voltage than this? (R1 & R2 should be connected each other and also C2, though they are not connected in schematic I posted in the first posted, and should be corrected as follows)

-8dBm is 89mV according to my calculations.

If you want a logic output I would look for a high speed comparator and AC couple to it, with some biasing resistors.

Keith

You have never indicated what is your frequency and load impedance. The capacitors C2 and C3 are good for > 10 MHz. A 2N2222 transistor should be a good RF amplifier for up to >100 MHz. Use it at 12V DC and use AC coupling to the following TTL load.