SL1613

Fig.10 Circuit diagram of low strip

Fig.9 Suitable interstage tuned circuit

Fig.8 Direct coupled amplifiers

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 parallel or series circuit cannot be used. This 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 gain at

resonance.

A single capacitor may not be suitable for decoupling the

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

Values of supply line decoupling capacitor required for

untuned cascades are given below. Smaller values can be

used in high frequency tuned cascades.

The amplifiers have been provided with two ground 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 on-chip 500pF supply decoupling capacitor has a

resistance of, typically 10

Ω. 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).

Number of stages

6 or more

5

4

3

Minimum capacitance

30nF

10nF

3nF lnF

Centre frequency

60MHz

Dynamic Range

-75dBm to +15dBm

Video rise time

70nSec

Bandwidth

approx. 20MHz

Output voltage

0 - 1.5V

Typical log accuracy

±2dB