metalbeard
New Member
Hello:
Am designing an FSK transmitter but in an old fashion way am using two sinewave oscillator (each on dependent frequency for 1s and 0s) which is wein bridge oscillator with an AGC as shown in the circuit below but the problem is that I couldn't know why is the grounding on the invert input of the op-amp and if it is correct how can I detrmine the gain of this op-amp.
As they are describing in the application note (that I got this circuit from) that the JFET serves as the AGC element, its gate voltage is zero when the power is applied leading to a low drain-to-source resistance (RDS). This places RG2+RS+RDS in parallel with RG1, raising the gain to 3.05, and as the output voltage grows, RDS increases, lowering the gain until the stabilization of the circuit which has the gain of 3
GAIN=(1+RF/( (RG2+RS+RDS)//RG1) ).
So I would be very happy if any one could help me finding the calculations of the gain of this circuit and how they got the 3.05 (assuming that RDS=zero when the power is applied).
(if the circuit doesn't appear click on the link)
http://www.geocities.com/metalbeard/index.html
**broken link removed**
Am designing an FSK transmitter but in an old fashion way am using two sinewave oscillator (each on dependent frequency for 1s and 0s) which is wein bridge oscillator with an AGC as shown in the circuit below but the problem is that I couldn't know why is the grounding on the invert input of the op-amp and if it is correct how can I detrmine the gain of this op-amp.
As they are describing in the application note (that I got this circuit from) that the JFET serves as the AGC element, its gate voltage is zero when the power is applied leading to a low drain-to-source resistance (RDS). This places RG2+RS+RDS in parallel with RG1, raising the gain to 3.05, and as the output voltage grows, RDS increases, lowering the gain until the stabilization of the circuit which has the gain of 3
GAIN=(1+RF/( (RG2+RS+RDS)//RG1) ).
So I would be very happy if any one could help me finding the calculations of the gain of this circuit and how they got the 3.05 (assuming that RDS=zero when the power is applied).
(if the circuit doesn't appear click on the link)
http://www.geocities.com/metalbeard/index.html
**broken link removed**