SL521

Fig.5 Maximum rectified output current v. temperature

(typical)

Fig.6 Noise figure v. temperature (typical)

Fig.7 Input admittance with open-circuit output (typical)

Fig.8 Direct Coupled amplifiers

Fig.9 Suitable interstagetuned circuit

OPERATING NOTES

The amplifiers are intended for use directly coupled, as

shown in Fig 8.

The seventh stage in an untuned cascade will be giving

virtually full output on noise.

Noise may be reduced by inserting a single tuned circuit in

the chain As there is a large mismatch between stages a

simple shunt or series circuit cannot be used The choice of

network is also controlled by the need to avoid distorting the

logarithmic law; the network must give unity voltage transfer at

resonance A suitable network is shown in Fig 9. The value of

C1 must be chosen so that at resonance its admittance equals

the total loss conductance across the tuned circuit Resistor R1

may be introduced to improve the symmetry of filter response,

providing other values are adjusted for unity galn at

resonance.

A simple capacitor may not be suitable for decoupling the

output line if many stages and fast rise times are required.

Alternative arrangements may be derived, based on the

parasitic parameters given.

Values of positive supply line decoupling capacitor

requlred for untuned cascades are given below. Smaller

values can be used in high frequency tuned cascades.

Number of stages

6 or more

5

4

3

Minimum capacitance

30nF

10nF

3nF lnF

The amplifiers have been provided with two earth leads to

avoid the introduction of common ground lead inductance

between input and output circuits. The equipment designer

should take care to avoid the subsequent introduction of such

inductance.

The 500pF supply decoupling capacitor has a resistance

of, typically, 1 0Q. It is a junction type having a low breakdown

voltage and consequently the positive supply current will

increase rapidly if the supply voltage exceeds 7.5V (see

Absolute Maximum Ratings).