10MHz peak measurement

Hi Jesse. What rectifier are you using? At these frequencies, the diode switching speed may be an issue. And what value and type of cap? Some caps are good for high frequencies and some aren't. Are you using a resistor in series to the cap? If not, the instantaneous current is probably limiting the effective "smoothing." It sounds like an RC filter might be the key. Or even better an op-amp precision rectifier, do a search for "TI Op Amps for Everybody" and you should find an excellent TI website and resource. This would probably work better but be more complex.

Perhaps you could try a rectifier and 4th-order RC filter network, like this:

AC in D1 100k 100k 100k 100k DC out |---//--+--//--+--//--+--//--+----->

FAST |+ |+ |+ |+ (buffer with a --- --- --- --- unity-gain op amp) --- --- --- --- | 10nF | 10nF | 10nF | 10nF | | | | ----- ----- ----- ----- --- --- --- --- - - - -

You could feed this a 1kHz 50% duty cycle squarewave signal and get a nice, smooth DC voltage out. Exact values and methodology left to experimentation.

-M

Oh and I forgot to mention, that the voltage of an AC waveform will change as it is rectified into DC. For instance, if you rectify a

12vAC signal into DC, it would be pulsating DC with a peak of about 17 volts. AC is termed as the RMS (root-mean-square) voltage measurement of a sinusoidal waveform. 12vAC is 17vPP (peak to peak.)

See

for more info.

That said, it is possible to perform mathematical functions by using only op amps...

-M

ADC).

but

faster

See this thread of mine from a few years back:

(hope the link works)

I used an AD8037 high speed clamping amplifier in a novel full-wave precision rectifier configuration from an AD app note. This gives a precision peak detector which converts the sine wave into a DC value equal to the peak of the waveform. It actually worked to more than

20MHz over a voltage range similar to yours if memory serves me correctly.

Dave :)

You are describing the function of a AM RF detector operating ~ 10 MHZ , a little pickier than a garden variety 455 KC AM Detector . Your requirements for a Wide-Bandwidth is contrary to several generations of Ultra narrow band designs, so you must back-engineer any modern circuit to increase the bandwidth. Things like TRF amplifiers come to mind as opposed to HiQ IF amplifiers. Just build an AM detector that will demodulate the local AM station and go from there. Most OP Amps I've seen quit around 100KC so you would have to find one that would work to around 20 MHZ . Diode Detectors can be found that will work all the way into the GigaHertz range, the output of which should in the ~ subsonic range ie 10's of seconds per Cycle, duck soup for standard garden variety OP amps. Would a Voltage controlled Amplifier help ? ie take the error Voltage from a PLL circuit monitoring the Incoming Signal Frequency to adjust the gain of the Output amplifier to track the frequency shift and flatten the output response

Yukio VE5YS

Davy, welcome out of your locker.