EMRFD Message Archive 15277
Message Date From Subject 15277 2019-05-11 03:49:59 peter_dl8ov Multiple Op Amps on A Single Supply I want to build a distribution amplifier for the reference signal provided by my GPSDO, this will use 2 x OPA4820 chips which each contain four op amps and there will be a single supply of 9V. I am however a little confused when it comes to running multiple op amps in parallel.
The feedback resistor Rf runs from the output to the inverting input and the gain resistor Rg is connected from the inverting input to ground. There is a voltage divider connected to the non-inverting input that provides 4.5V bias, the input is also connected to the 4.5V point via a capacitor.
Do I need to duplicate the voltage divider and input capacitor for each op amp or can I have only one bias and input capacitor network and connect all of the non-inverting inputs together?
15278 2019-05-11 05:17:07 John Re: Multiple Op Amps on A Single Supply You can run all the op amps from a single bias supply.
15279 2019-05-11 05:24:14 Roelof Bakker Re: Multiple Op Amps on A Single Supply Hello Peter,
You might consider looking at the datasheet of the LMH6559.
This is a buffer amplifier with a gain of 1 and multiple outputs can be created by using n-number of 50
ohm resistors at the output.
15280 2019-05-11 06:02:10 Roelof Bakker Re: Multiple Op Amps on A Single Supply Hello Peter,
Just read your post better.
>>>can I have only one bias and input capacitor network and
connect all of the non-inverting inputs together?
The answer is yes.
15281 2019-05-11 11:44:37 sailvalis Re: Multiple Op Amps on A Single Supply You can connect the non-inverting inputs together. You will need independent Rf and Rg resistors for each opamp.But if you are using a single 9V supply (+9v and Gnd), then your Rg resistor can't go to ground, it needs to go to a half-supply voltage similar to that provided by the non-inverting input voltage divider. The simplest way to do this is to connect two voltage-divider resistors at the inverting input, each double the value of the desired Rg. Alternately, you can create a well-bypassed half-supply voltage and then bias the op amp inputs from that (using series resistors).I hope you realize that the OPA4820 draws about 20mA from the power supply. This is going to flatten an alkaline 9V battery in about 24 hours. Your voltage dividers are going to take a few mA as well. 15282 2019-05-11 11:45:42 Jim Strohm Re: Multiple Op Amps on A Single Supply 15283 2019-05-12 01:53:22 peter_dl8ov Re: Multiple Op Amps on A Single Supply Thanks for all the replies, you've put my mind at rest regarding the bias resistors and today I'll start melting some solder. Current drain at 20mA each is not a problem as the wall wart supplying the GPSDO has power to spare, it's 9V at 3A.
Finally, yes, lots of bypassing including an SMT 100n glued to the top of each chip and then connected across the power pins. I work with SMT down to 0201 three days a week so this will be an easy build.
After that, pull the shack apart so that I can run the 10 MHz cables :(