CIRCUIT ARRANGEMENT FOR A TELEVISION OR RADIO RECEIVER FOR SWITCHING A TUNING VOLTAGE FROM A PRESET TUNING POTENTIOMETER TO A VOLTAGE CONTROLLABLE TUNING ELEMENT AT WILL

摘要

1447869 Receiver tuning arrangements; transistor analogue gates and current mirror circuits PHILIPS ELECTRONIC & ASSOCIATED INDUSTRIES Ltd 6 Sept 1973 [9 Sept 1972 25 May 1973] 41922/73 Headings H3Q and H3T In a circuit arrangement for a TV or radio receiver for switching a tuning voltage of a tuning potentiometer 1, Fig. 1, to a voltage controllable tuning element 3 by means of an impedance converter T 1 , T 2 , T 6 Fig. 2 and a switch T 7 , T 8 identical switching elements T 7 , T 8 interconnect the tuning potentiometer 1 to the tuning element 3 when activated by a switchable current source T 9 , T 10 and the arrangement is such that current flowing across a junction of one T 7 of the switching elements is matched by an equal current flowing in a corresponding sense across the corresponding junction of the other switching element T 8 . As shown in Fig. 2 an emitter follower T 6 provides the impedance conversion while a difference amplifier T 1 , T 2 and current mirror T 3 , T 4 , T 5 provide for U BE and temperature compensation. The tuning voltage at 8 is prevented from occurring at the output A when T 9 is turned on by control at 12 so as to turn off the analogue switch T 7 , T 8 . In a modification Fig. 3, the analogue switch transistors T 20 , T 21 are switched off when a transistor T 25 is turned on. A transistor T 24 provides negative feedback to T 21 so as to make the collector currents of T 23 and T 21 equally large. The current mirror transistors T 22 and T 23 may have a high current amplification # of 98 and operate the same as the current mirror of Fig. 2 which has three transistors T 3 , T 4 , T 5 because (lateral) PNP transistors only have low # such as 2-15. The current generator T 12 , T 26 is common for all electronic analogue switches such as 2, 5 Fig. 1, and is necessary to recharge the hum and interference filter capacitor connected to the output in a period after switch over of tuning. In a modification of Fig. 3 an output amplifier (T 24 , T 42 , Fig. 4, not shown) replaces the emitter follower T 24 of Fig. 3. This output amplifier is common for all programmes and includes a plural collector transistor (T 42 ) constituting a current mirror. The tuning voltage may be indicated by a voltmeter (50) connected to the output A. In a further arrangement (Fig. 5, not shown) a plurality of impedance converting analogue switches each consist of transistor pairs T 1 a, T 2 a, T 1 b, T 2 b having their outputs connected to a common output emitter follower T 6 and also connected to a common current mirror T 3 , T 4 , T 5 . The circuit arrangement may be constructed in integrated circuit form.