This design provides single-ended, adjustable gain from 15 dB to 40 dB with extremely high input impedance at a very low frequency response. The power consumption is optimized for battery-powered audio applications.

• The JFE2140 is configured as a differential pair in a voltage-feedback composite amplifier. This configuration allows for low-frequency gain without large dc-blocking capacitors.
• The bias current is set by selecting the desired bias current and noise tradeoff (see Figure 6-16). To set the bias current point, adjust the source resistance according to Figure 9-4.
• After the bias current is selected, set the JFET stage gain as high as possible. To avoid pushing the device into the linear region of operation, use the largest drain resistor (R_D1,2) possible while maintaining a minimum of 1 V across the drain-to-source nodes.
• The overall gain can be configured with the feedback resistors R_F1, R_F2 and R_F3. Capacitor C_F3 can be required depending on the gain configuration for amplifier stability; use amplifier stability best practices to maintain stability at both maximum and minimum gain configurations.