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Buffer Amp IC suggestions plse
Hi,
Ive been trying to locate a suitable unity gain buffer amplifier IC that can drive a 50 load. Application is to buffer a VCO output at 5Mhz. Needs to be 8pin DIP and operate on a single-ended supply. I had found what I wanted in the CLC109, but cant seem to find a supplier. Any suggestions greatly appreciated regarding type and supplier that is user friendly to international countries. JEFF ZL3JK New Zealand |
Jeff wrote...
Ive been trying to locate a suitable unity gain buffer amplifier IC that can drive a 50 load. Application is to buffer a VCO output at 5Mhz. Needs to be 8pin DIP LTC's LT1206 comes in TO220, miniDIP and soic packages, and Digi-Key has them in stock for $6.25 each... http://rocky.digikey.com/WebLib/Line...ata/LT1206.pdf http://www.digikey.com/scripts/DkSea...ail?Ref=329191 and operate on a single-ended supply. Oops, +/-5V supply. What's your signal voltage? And did you want your output to have a 50-ohm source impedance? -- Thanks, - Win |
Needs to drive into 50 ohms. input level approx 150mV at 5Mhz
"Winfield Hill" wrote in message ... Jeff wrote... Ive been trying to locate a suitable unity gain buffer amplifier IC that can drive a 50 load. Application is to buffer a VCO output at 5Mhz. Needs to be 8pin DIP LTC's LT1206 comes in TO220, miniDIP and soic packages, and Digi-Key has them in stock for $6.25 each... http://rocky.digikey.com/WebLib/Line...ata/LT1206.pdf http://www.digikey.com/scripts/DkSea...ail?Ref=329191 and operate on a single-ended supply. Oops, +/-5V supply. What's your signal voltage? And did you want your output to have a 50-ohm source impedance? -- Thanks, - Win |
Jeff wrote:
Hi, Ive been trying to locate a suitable unity gain buffer amplifier IC that can drive a 50 load. Application is to buffer a VCO output at 5Mhz. Needs to be 8pin DIP and operate on a single-ended supply. I had found what I wanted in the CLC109, but cant seem to find a supplier. Any suggestions greatly appreciated regarding type and supplier that is user friendly to international countries. JEFF ZL3JK New Zealand An AD817 can deliver +-50 mA and has a gain bandwidth product of 50 MHz. http://www.analog.com/UploadedFiles/...66266ad817.pdf 4$ from Digikey. Good for either a gain 1 buffer or a gain 2 with series 50 ohm resistor, 50 ohm source. |
Jeff wrote...
Needs to drive into 50 ohms. input level approx 150mV at 5Mhz Winfield Hill wrote ... Jeff wrote... Ive been trying to locate a suitable unity gain buffer amplifier IC that can drive a 50 load. Application is to buffer a VCO output at 5Mhz. Needs to be 8pin DIP LTC's LT1206 comes in TO220, miniDIP and soic packages, and Digi-Key has them in stock for $6.25 each... http://rocky.digikey.com/WebLib/Line...ata/LT1206.pdf http://www.digikey.com/scripts/DkSea...ail?Ref=329191 and operate on a single-ended supply. Oops, +/-5V supply. What's your signal voltage? And did you want your output to have a 50-ohm source impedance? Unless you source with 50 ohms (2x signal plus 50-ohm resistor), and terminate with 50-ohms, the issue becomes how much cable capacitance? Either the load looks resistive (100 ohms in the former case) or capacitive. -- Thanks, - Win |
Thanks. The AD817 looks good, and I can source it locally from Australia.
Thanks all for your help. JEFF "John Popelish" wrote in message ... Jeff wrote: Hi, Ive been trying to locate a suitable unity gain buffer amplifier IC that can drive a 50 load. Application is to buffer a VCO output at 5Mhz. Needs to be 8pin DIP and operate on a single-ended supply. I had found what I wanted in the CLC109, but cant seem to find a supplier. Any suggestions greatly appreciated regarding type and supplier that is user friendly to international countries. JEFF ZL3JK New Zealand An AD817 can deliver +-50 mA and has a gain bandwidth product of 50 MHz. http://www.analog.com/UploadedFiles/...66266ad817.pdf 4$ from Digikey. Good for either a gain 1 buffer or a gain 2 with series 50 ohm resistor, 50 ohm source. |
On Thu, 22 Sep 2005 09:14:55 +1200, Jeff wrote:
Hi, Ive been trying to locate a suitable unity gain buffer amplifier IC that can drive a 50 load. Application is to buffer a VCO output at 5Mhz. Needs to be 8pin DIP and operate on a single-ended supply. I had found what I wanted in the CLC109, but cant seem to find a supplier. Any suggestions greatly appreciated regarding type and supplier that is user friendly to international countries. JEFF ZL3JK New Zealand What you want is a video buffer or video op-amp. Linear Technologies, National Semiconductor, and Analog Devices are among the many companies that make such things. Note that some of these devices get a bit squirrelly if they see a capacitive load. So I recommend that you do something like this: (use courier or other constant-width font for ASCII art schematic) |\ 50 in--|+\__+____/\/\____/ to 50 Ohm load +--|-/ | | |/ | | | +--/\/\-+ | Rf \ /Ra \ / | ----- GND Rf and Ra would be the same value. Use a value recommended by the datasheet, or 1k if the datasheet doesn't recommend a specific value. Follow any other suggestions in the datasheet as well. For example, they may suggest a small capacitor directly from the op-amp output to inverting input. You probably want to terminate the input with a 50 Ohm resistor, too, but I don't know, so I'll leave it out. It sounds like you may need AC-coupling, so you can put blocking capacitors on the input and/or output. Oh, if you put a blocking cap on the input, be sure to also provide a DC (resistive) path to GND or to the mid-rail point if you are going single-supply. Just chose a capacitor big enough so that 1/(2*pi*R*C) is much lower than 5 MHz, your signal of interest. (R in this case is 50 Ohms) There is no problem putting a capacitor like this in the signal path: Since it looks like a short circuit at higher frequencies, it does not capacitively load the amp at frequencies where the amp might be unstable. Also, the series 50 Ohm resistor keeps the overall impedance resistive. HTH --Mac |
On Wed, 21 Sep 2005 15:25:09 -0700, Winfield Hill wrote:
Jeff wrote... Ive been trying to locate a suitable unity gain buffer amplifier IC that can drive a 50 load. Application is to buffer a VCO output at 5Mhz. Needs to be 8pin DIP LTC's LT1206 comes in TO220, miniDIP and soic packages, and Digi-Key has them in stock for $6.25 each... http://rocky.digikey.com/WebLib/Line...ata/LT1206.pdf http://www.digikey.com/scripts/DkSea...ail?Ref=329191 and operate on a single-ended supply. Oops, +/-5V supply. What's your signal voltage? And did you want your output to have a 50-ohm source impedance? Maybe an LT1191? digikey #: LT1191CN8-ND (24 in stock at USD 3.25) http://rocky.digikey.com/WebLib/Line...ata/LT1191.pdf --Mac |
Mac wrote...
Maybe an LT1191? digikey #: LT1191CN8-ND (24 in stock at USD 3.25) http://rocky.digikey.com/WebLib/Line...ata/LT1191.pdf Ouch, a 30mA supply current! -- Thanks, - Win |
Winfield Hill wrote: Mac wrote... Maybe an LT1191? digikey #: LT1191CN8-ND (24 in stock at USD 3.25) http://rocky.digikey.com/WebLib/Line...ata/LT1191.pdf Ouch, a 30mA supply current! Well- why not your super-duper 74HCU04 linear amp or whatever it was?- is that available in Tiny Logic? |
Thanks for those ideas. I was considering putting a low pass filter after
the amp. The 2 shunt caps work out to be 560pF each. JEFF "Mac" wrote in message ... On Thu, 22 Sep 2005 09:14:55 +1200, Jeff wrote: Hi, Ive been trying to locate a suitable unity gain buffer amplifier IC that can drive a 50 load. Application is to buffer a VCO output at 5Mhz. Needs to be 8pin DIP and operate on a single-ended supply. I had found what I wanted in the CLC109, but cant seem to find a supplier. Any suggestions greatly appreciated regarding type and supplier that is user friendly to international countries. JEFF ZL3JK New Zealand What you want is a video buffer or video op-amp. Linear Technologies, National Semiconductor, and Analog Devices are among the many companies that make such things. Note that some of these devices get a bit squirrelly if they see a capacitive load. So I recommend that you do something like this: (use courier or other constant-width font for ASCII art schematic) |\ 50 in--|+\__+____/\/\____/ to 50 Ohm load +--|-/ | | |/ | | | +--/\/\-+ | Rf \ /Ra \ / | ----- GND Rf and Ra would be the same value. Use a value recommended by the datasheet, or 1k if the datasheet doesn't recommend a specific value. Follow any other suggestions in the datasheet as well. For example, they may suggest a small capacitor directly from the op-amp output to inverting input. You probably want to terminate the input with a 50 Ohm resistor, too, but I don't know, so I'll leave it out. It sounds like you may need AC-coupling, so you can put blocking capacitors on the input and/or output. Oh, if you put a blocking cap on the input, be sure to also provide a DC (resistive) path to GND or to the mid-rail point if you are going single-supply. Just chose a capacitor big enough so that 1/(2*pi*R*C) is much lower than 5 MHz, your signal of interest. (R in this case is 50 Ohms) There is no problem putting a capacitor like this in the signal path: Since it looks like a short circuit at higher frequencies, it does not capacitively load the amp at frequencies where the amp might be unstable. Also, the series 50 Ohm resistor keeps the overall impedance resistive. HTH --Mac |
Try a SL560
"Jeff" schreef in bericht ... Hi, Ive been trying to locate a suitable unity gain buffer amplifier IC that can drive a 50 load. Application is to buffer a VCO output at 5Mhz. Needs to be 8pin DIP and operate on a single-ended supply. I had found what I wanted in the CLC109, but cant seem to find a supplier. Any suggestions greatly appreciated regarding type and supplier that is user friendly to international countries. JEFF ZL3JK New Zealand |
Winfield Hill wrote:
Jeff wrote... Needs to drive into 50 ohms. input level approx 150mV at 5Mhz Winfield Hill wrote ... Jeff wrote... Ive been trying to locate a suitable unity gain buffer amplifier IC that can drive a 50 load. Application is to buffer a VCO output at 5Mhz. Needs to be 8pin DIP LTC's LT1206 comes in TO220, miniDIP and soic packages, and Digi-Key has them in stock for $6.25 each... http://rocky.digikey.com/WebLib/Line...ata/LT1206.pdf http://www.digikey.com/scripts/DkSea...ail?Ref=329191 and operate on a single-ended supply. Oops, +/-5V supply. What's your signal voltage? And did you want your output to have a 50-ohm source impedance? Unless you source with 50 ohms (2x signal plus 50-ohm resistor), and terminate with 50-ohms, the issue becomes how much cable capacitance? Either the load looks resistive (100 ohms in the former case) or capacitive. I would say it depends on the cable you choose. If there is a 50 Ohm load and you connect it to your buffer amplifier with 50 Ohm coaxial cable, then the buffer amplifier will see a 50 Ohm resistive load, not capacitive at all. It is probably still wise to use the gain-of-two amplifier and 50 Ohm source resistor in case the load happens to be a poor match. If you really don't need this feature then I would be tempted to use an emitter follower with just one transistor. (Do they make transistors in DIP-8 packages?) Chris |
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