Preamplifiers bandwidth

It is also true that some lock-in amplifiers as well as tuned preamplifiers allow the user to select the Q of the tuned amplifiers. The Q of an amplifier is given approximately by Q f0jBW, where f0 is the center frequency and BW the full bandwidth. The system bandwidth must be carefully and properly selected when recording data to be deconvolved, and all factors that influence the system bandwidth must be carefully taken into account. 

In general, the spatial resolution of PSD s is a function of the signal to noise ratio after the preamplifiers. Since the noise amplitude is proportional to the bandwidth of the amplifier stages, it is absolutely necessary to select this bandwidth such that the maximum information, timing or amplitude, is extracted from the signal, and that the minimum amount of noise is passed. 

The receiver system consists of a preamplifier (Radiation Devices model BBA-1P, bandwidth 3-500 MHz at 15 dB gain and 3 dB noise), a 10 MHz amplifier (F+H Instruments mixer-amplifier, model 39 A/M), and a phase detector (F+H Instruments phase detector 1-30 MHz). 

At first glance it may appear necessary to build an amplifier fast enough so that it does not broaden the detector pulses. This would require about 1 GHz for conventional PMTs and more than 3 GHz for MCPs. However, in practice the signal bandwidth is limited by the discriminators in the CFD as well. The input bandwidth of the discriminators is usually of the order of 1 GHz, so that an amplifier bandwidth above 1 to 2 GHz does not improve the timing performance noticeably. More important than extreme bandwidth are linearity and low noise, especially low noise pickup from the environment (see Sect. 7.5.4, page 311). A good preamplifier should amplify the detector pulses without noticeable nonlinearity up to the maximum CFD threshold of the TCSPC module, i.e. about 500 mV. This is no problem for the amplifiers used in the circuit shown in Fig. 7.38. 

High signal-to-noise ratios thus require the use of very low noise amplifiers and the limitation of bandwidth. The current technology offers differential amplifiers with voltage noise of less than 10 nV/VHz and current noise less than 1 pA/VHz. Both parameters are frequency dependent and decrease approximately with the square root of frequency. The exact relationship depends on the technology of the amplifier input stage. Field effect transistor (FET) preamplifiers exhibit about 5 times the voltage noise density compared to bipolar transistors but a current noise density that is about 100 times smaller. 

The purpose of the high- and low-pass filters, shown in Figure 9.2, is to eliminate interference signals such as electrode half-cell potentials and preamplifier offset potentials and to reduce the noise amplitude by the limitation of the amplifier bandwidth. Because the biosignal should not be distorted or attenuated, higher order sharp-cutting linear-phase filters have to be used. Active Bessel filters are preferred filter types because of their smooth transfer function. Separation of biosignal and interference is in most cases incomplete because of the overlap of their spectra. 

Strength and the sample concentration, po is the permeability of free space, Q is the quality factor of the coil, coo is the Larmor angular frequency, K is the volume of the coil, F is the noise figure of the preamplifier, k is Boltzmann s constant, is the probe (as opposed to sample) temperature, and A/is the bandwidth (in Hz) of the receiver. It can be seen that the concentration sensitivity 5c (SIN per pM concentration of analyte) is poor for microcoils. This is due to the fact that microcoil probes have very small observation volumes and therefore contain a very small amount of analyte. However, if the sample can be concentrated into a small volume, then the microcoil can more easily detect the signal. This high mass sensitivity 5m (SIN per pmol of analyte) is characteristic of microcoil NMR probes. In essence, the use of microcoil probes enhances the mass sensitivity 5m at the expense of the concentration sensitivity 5c. To better understand the relationship between sensitivity and coil diameter, a detailed analysis was reported by Peck et Their results showed that mass sensitivity increases monotonically with decreasing coil diameter within the 1mm to 50 pm range they studied. However, the concentration sensitivity decreases, and therefore there is a trade-off between Sc and 5m that depends on coil diameter. 

In the practical applications, the concentration of luminescent species is usually very low and consequently a photomultiplier is commonly used as a detector. If the emission can be efficiently focused into a small entrance, an avalanche diode can also be used. A reasonably fast detector is anyway needed also in the frequency-domain method due to the phase error induced by the detector. StiU the requirements are not as strict as in the case of prompt organic fluorophores. In the case of the most commonly used lanthanides, the upper limit of modulation is around 100 kHz, but still the reasonably error-free phase detection requires ca. 1 MHz bandwidth from the detector and accompanying current-to-voltage preamplifier. 

Consider the system comprising an amplifier and filter shown in Fig. 10. If this arrangement is followed by an ideal photodetector, with a quantum efficiency of ri = I, then the complete combination may be analyzed as an ideal optically preamplified receiver. In the following, all optical powers are represented as their photocurrent equivalents, e.g., iin = Pinq/hv, and it is assumed that the electrical detection system has a bandwidth. The photocurrent equivalent of the spontaneous emission power isp is... 

The design, fabrication and characterization of novel micromachined focused ultrasonic transducers for minimally invasive medical imaging procedures have been demonstrated. Transducers were fabricated using a membrane deflection technique to produce spherical sections in a piezoelectric polymer film. Pulse echo responses showed minimal ringing and wide bandwidths characteristics of 80-110 %. Axial resolution of 50 pm and lateral resolution of 51-92 pm were achieved. A preamplifier circuit incorporated into a hybrid package with the ultrasonic transducer exhibited thermal nmse of 5.3 nV/Hz. The transducers were used to image human cadaveric aorta to reveal high-resolution subsurface structures. 

The detector is protected from external noise by enclosing it within a grounded metallic box, and power is supplied via a local filter. Those circuits that are sensitive to electronic noise (mixers and preamplifiers) were isolated with the help of aluminum cases connected to the analog ground of the electronic assembly. The assembled selective microvoltmeter assembled detector was evaluated for its sensitivity, linearity, and pass bandwidth. This study was carried out with the help of a calibrated HF generator that was attached to a calibrated attenuator and so provided a sinusoidal voltage of amplitude 0.1-500 p,V and a frequency tunable between 0.5 and 8 MHz. 

M. Carminati, G. Ferrari, D. Bianchi and M. Sampietro, Femtoampere integrated current preamplifier for low noise and wide bandwidth electrochemistry with nanoelectrodes, Electrochimica Acta, 2013, Vol. in press. 

J. Rosenstein, V. Ray, M. Dmdic and K. L. Shepard, Solid-state nanopores integrated with low-noise preamplifiers for high-bandwidth DNA analysis, Proc. lEEEINIH Life Science Systems and Applications Workshop, 2011, 59-62. G. Ferrari, M. Farina, F. Guagliardo, M. Carminati and M. Sampietro, Ultra-low-noise CMOS current preamplifier from DC to 1 MHz, Electronics Letters, 2009, 1278-1280. 

---