. Electronic apparatus for biological research. Electronic apparatus and appliances; Biology -- Research. put 2. Figure Ret. wave in Figure It is interesting to consider the possibility of using apparatus such as that of Neale and Oakes as a pre-amplifier for use with micro electrodes in electrophysiology. If the zero stability is 10~^ amps, then if the amplifier is fed from a 20 MQ microelectrode, the corresponding noise voltage at the electrode tip is 20 mV. The penetration of a cell (70 mV input or thereabouts) could probably be detected, but the device is likely to be too noisy
. Electronic apparatus for biological research. Electronic apparatus and appliances; Biology -- Research. put 2. Figure Ret. wave in Figure It is interesting to consider the possibility of using apparatus such as that of Neale and Oakes as a pre-amplifier for use with micro electrodes in electrophysiology. If the zero stability is 10~^ amps, then if the amplifier is fed from a 20 MQ microelectrode, the corresponding noise voltage at the electrode tip is 20 mV. The penetration of a cell (70 mV input or thereabouts) could probably be detected, but the device is likely to be too noisy for the extracellular recording of discharges from neighbouring cells. Carrier amplifiers—There is no difficulty, in principle, in making a transistorized carrier amplifier merely by interposing an coupled transistor amplifier between a relay chopper and a relay phase-sensitive rectifier; yet this is seldom done. An important characteristic of transis- torized devices is their small size, and there is little to be gained by using a very small amplifier if it works between two large relays. Consequently, designs for carrier amplifiers employing transistors involve chopper and rectifier devices of smaller proportions. Some of these invoke the almost perfect performance of the recently developed silicon signal diode. We have seen in Chapter 5 how diode networks can be used for phase-sensitive rectification; the same circuits can also be used to chop. For example, the arrangement in Figure (which, if R is replaced by a capacitance, we have hitherto regarded as a quasi-Cowan bridge rectifier) can clearly be used as a chopper. When the reference wave transformer drives current clockwise round the diode circuit, the diodes are switched to low resistance and the output is short-circuited. When the reference wave reverses, the diode resistances become very high. The magnitude of the output depends on the input, and also on the ratio 698. Please note that these images are e
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