| 摘要 |
<p>1,156,559. Logarithmic amplifiers. ATOMIC ENERGY OF CANADA Ltd. 11 Nov., 1966 [28 Dec., 1965], No. 50696/66. Heading G4G. A logarithmic amplifier in an ionization detector of a nuclear reactor comprises (Fig. 1) an ionization chamber 1 connected over cable 2 to the input 3 of an insulated gate field effect transistor input amplifier 4 feeding an operational amplifier 6 having a stabilized network 8 energizing a cas-code output amplifier 10 whose low impedance output is connected over cable 12 to a differentiator 14 operative to shut down a reactor when the differentiator output increases at an excessive rate in response to ionization chamber current. A feedback loop from amplifier 10 includes attenuator 16, a temperature drift compensating network 18 of silicon planar transistors Q3, Q4, and a logarithmic element 20 comprising series silicon planar transistors Q1, Q2 connected as emitter-base diodes to the input of stage 4. In network 18, the transistors are connected in polar opposition to Q1, Q2 and pass an average emitter current equal to the maximum expected current through Q1, Q2. The base of Q3 is earthed over temperature compensation resistor R1 correcting for varying temperature characteristics of Q1, Q2. A time constant condenser C1 shunts elements Q1, Q2 to smooth out minor fluctuations of the ionization current, and a further feedback path from the output of 10 to the input of 4 is provided over diode Dl and resistors R2, R3 to limit the maximum time constant of the feedback path to a predetermined value when the resistance of elements Q1, Q2 tends to infinity. The mode of temperature compensation is described in detail (Figs. 2a, 2b, 2c, not shown) and a more developed circuit is also described (Fig. 3, not shown).</p> |
