Random noise origin is often involved in examining many case of electronic systems such as filter, sound, or RF communication. The electrical circuit introduced here gives an RMS amplitude modulated noise source with selectable bandwidth. With 1 KHz to 5 MHz decade ranges selectable bandwidth and 300mV RMS output, this noise generator is appropriate for broad range of practical application. Here is the circuit :
Noise is generated by D1 that is AC conjugated to A2, an amplifier with broadband gain 100. The output of A2 is flowed to a mere selectable low-pass filter. The filter’s output is utilised to LT1228 operational transconductance amplifier A3. A3’s output courses electric current feedback amplifier LT1228 A4. A4’s output, which is also the circuit’s output, is tried by the A5-based gain control form. This closes down a gain control loop to A3. A3’s ISET current controls gain, admitting total output level control.
Schematic Diagram source : Linear Technology Application Note