Organize and Share your Electronics the way you want. Sign-Up for a free account now. It takes only 30 seconds!

Low Noise Amplifier for Phase Noise Measurements

Low Noise Amplifier for Phase Noise Measurements

Features less input noise than a 50 ohm resistor.
The phase noise of low noise oscillators and signal sources is usually determined by measuring the audio noise voltage at the output of the phase comparator in a phase-locked loop. The phase comparator is typically a low noise doubly-balanced mixer with a phase slope from a few tenths of a volt per radian to a few volts per radian. The low conversion gain of this type of phase detector yields a signal in the low nanovolt per root-hertz range for very low noise sources which is a level below the noise floor of most spectrum analyzers. Suitable low noise preamplifiers are readily constructed from discrete components or from modern low-noise op-amps.

Except for the noise voltage, the amplifier requirements are not particularly demanding. Since the output impedance of the phase detector is low, the input impedance of most amplifier circuits is adequate. A frequency response from a few hertz to 100kHz is usually adequate and the output load is usually a high impedance spectrum analyzer and oscilloscope. The phase detector output impedance is quite low so the noise current of ordinary bipolar transistors is sufficiently low. For example, an ordinary 2N4403 transistor exhibits a noise voltage below 1 nanovolt at 10 Hz when the source is a typical Schottky diode mixer. Several op-amps are available with noise voltages below 3 nanovolts and a few are available with noise voltage below 1 nanovolt. Simple amplifiers built from any of these parts will perform well in most applications. Bulk-metal, wirewound, and metal film resistors exhibit little excess noise and should be used instead of carbon film or carbon composition types. Most potentiometers should be avoided since film and cermet types are quite noisy.

Visit Here for more.

 

More Articles to Read

LED traffic light
LED traffic light
Estimating Power for ADSP-BF561 Blackfin® Processors
Estimating Power for ADSP-BF561 Blackfin® Processors
Teach Your Arduino to Switch Itself Off!
Teach Your Arduino to Switch Itself Off!
Control a tracked robot with your mind (or joystick)
Control a tracked robot with your mind (or joystick)
A 400W (1kW Peak) 100A electronic load using linear MOSFETs
A 400W (1kW Peak) 100A electronic load using linear MOSFETs
Shirt Pocket Transceiver with the Si5351 and OLED
Shirt Pocket Transceiver with the Si5351 and OLED
All metal C930e webcam
All metal C930e webcam
The Soldering Tools That Make Your Life Easier
The Soldering Tools That Make Your Life Easier
App note: Operation evaluation of ultra low ON resistance MOSFET supporting quick charge for 1 c ...
App note: Operation evaluation of ultra low ON resistance MOSFET supporting quick charge for 1 cell Lithium ion battery protection
Synthesized Sidetone
Synthesized Sidetone

Top




Shares