IF AMPLIFIER

Abstract: Until now at least two types of mixer oscillator integrated circuits for tuners have to be developed. One for the symmetrical output mode and one for the asymmetrical output mode. To obtain a tuner, IF amplifier, and/or mixer oscillator integrated circuit that is suitable for both output modes the tuner comprises switching means, whereby in the asymmetrical mode one output of the tuner is coupled to ground.

Description: IF amplifier. The invention relates to a tuner. The invention further relates to an IF amplifier for use in such a tuner. The invention further relates to a mixer oscillator integrated circuit compπsing such an IF amplifier. Such a tuner, LF amplifier, and mixer oscillator integrated circuit are known m the art, and can be used in television receivers, radio receivers, and other applications. A disadvantage of the known tuner, IF amplifier and mixer oscillator integrated circuit is that there has to be two kinds of tuners, IF amplifiers and mixer oscillator integrated circuits Namely depending on the output of the tuner, a symmetπcal and an asymmetπcal version An object of the invention is to obtain a tuner, an LF amplifier and a mixer oscillator integrated circuit that can be used for both symmetπcal and asymmetπcal outputs To this end a first aspect of the invention provides a tuner as defined in claim 1. A second aspect of the invention provides an LF amplifier as defined in claim 4 A third aspect of the invention provides a mixer oscillator integrated circuit as defined in claim 5 In this way it is possible to use the same tuner, LF amplifier or mixer oscillator integrated circuit respectively for both kind of output signals, by switching the LF amplifier between the two modes and by coupling one output of the tuner to ground in the asymmetπcal mode In the symmetπcal output mode on both outputs of the tuner (LF amplifier, mixer oscillator integrated circuit respectively) a signal is present to be handed further Whereas in the asymmetπcal output mode only on one output an output signal is present and the other output is coupled to ground. An embodiment of a tuner according to the invention comprises the features of claim 2. By using a switchable LF amplifier the amplifier itself is switched between the two modes. Another embodiment of a tuner according to the invention comprises the features of claim 3. In this embodiment the LF amplifier comprises two amplifying means, one for the symmetrical mode and one for the asymmetrical mode and the control means decide which one has to operate. The invention and additional features, which may optionally be used to implement the invention to advantage, will be apparent from and elucidated with reference to the examples described below hereinafter and shown in the figures. Herein shows: Figure 1 a schematic example of a tuner according to the invention, and Figure 2 a schematic example of an LF amplifier according to the invention. Figure 1 shows a schematic example of a tuner T according to the invention. This tuner comprises an input 1 for receiving an input signal for example from an antenna, the input is coupled to an input circuit 3 for handling the input signal. The input circuit is coupled to a mixer oscillator stage 5 for obtaining and supplying the LF signal. The mixer oscillator stage supplies the LF signal (asymmetrical or symmetrical) via outputs Ol and 02 to a SAW (surface acoustic wave) filter 7 as it is referred to in the art. A general description of the operation of the tuner T is not necessary as this is generally known to the man skilled in the art. The mixer oscillator stage 5 comprises in this example a mixer oscillator integrated circuit 51. The mixer oscillator integrated circuit comprises an LF amplifier 511 and switching means 513 and control means 53 for controlling the switching means. It is to be noticed here that the switching means can (partly) be combined with the LF amplifier (as shown in figure 1 by the dashed overlap between LF amplifier 511 and switching means 513). The switching means 513 operate under control of the control means 53 to switch the IF amplifier between the two modes, that is the symmetrical and the asymmetrical mode. Further the switching means comprise a switch SW to couple one output (02 in this example) to ground in the asymmetrical mode. In this way it is possible to use the same tuner T, IF amplifier 511 or mixer oscillator integrated circuit 51 respectively for both output signals. In the symmetrical output mode on both outputs Ol and 02 of the tuner (IF amplifier, mixer oscillator integrated circuit respectively) a signal is present to be handed further. Whereas in the asymmetrical output mode only on one output Ol an output signal is present and the other output 02 is coupled to ground. Figure 2 shows an example of part of an mixer oscillator integrated circuit 251 according to the invention comprising the IF amplifier 2511 and the switching means 2513. The IF amplifier comprises an amplifying means AMP that receives the IF input signal(s) LF- LN at inputs IA21, IA22. Outputs OA21 and OA22 of the amplifying means are coupled via a transistor Ql and a resistor R5, respectively a transistor Q2 and a resistor R6 to the outputs 021 and 022. The transistors Ql and Q2 are both emitter followers at the output. The feedback resistors Rl, R2, R3 and R4 determine the gain of the LF amplifier 2511, whereby in this example the sum of the values of resistors Rl and R2 corresponds with the value of resistor R4. In the symmetrical mode switch SW22 of the switching means 2513 is open. In the asymmetrical mode the switch SW22 is closed and the gain is increased in the upper branch. In this way, it is possible to obtain a substantial equal overall gain in both the asymmetrical and the symmetrical mode. The DC current for the output emitter followers is set by current sources in this example implemented by transistors Q3, Q4 and Q5 as follows: In the symmetrical mode: Q3 and Q5 provide equal DC currents for Ql and Q2, Q4 is cut off. In the asymmetrical mode: Q5 is switched off. Q4 is switched on, doubling the DC current of Ql, compared to the symmetrical mode. This doubling is necessary as is well known to the man skilled in the art, if a minimal dissipation is required. In the symmetrical mode both outputs contain information and the DC current may be about half of the value required when the whole voltage swing is present at only output in the asymmetrical mode. Instead of one amplifying means as described above the invention can also be implemented with two amplifying means, one for the symmetrical mode and one for the asymmetrical mode. Also in this case one output (022 in figure 2) is coupled with switching means to ground in the asymmetrical mode. The man skilled in the art will be well aware of a lot of variations on the above- described examples using the same idea of invention. For example is it possible, not necessary, to incorporate the control means within the mixer oscillator integrated circuit. Figure 2 shows a very detailed example of part of the mixer oscillator integrated circuit, which of course is not the only way to implement the LF amplifier for this invention. Further switching means being either totally inside the mixer oscillator integrated circuit or partly inside, partly outside the mixer oscillator integrated circuit, or even totally outside the integrated circuit is possible. Ground may be any suitable reference voltage.

Claims: CLAIMS: 1. Tuner comprising an input circuit and a mixer oscillator stage, which mixer oscillator stage comprises an LF amplifier coupled to an output of the tuner, characterized in that the tuner comprises switching means for switching between a symmetrical and an asymmetrical output mode and whereby in the asymmetrical mode one output of the tuner is coupled to a reference voltage by the switching means, and the tuner comprises control means for controlling the switching operation. 2. Tuner as claimed in claim 1 characterized in that the IF amplifier is a switchable IF amplifier. 3. Tuner as claimed in claim 1, characterized in that the IF amplifier comprises a first and a second amplifying means whereby the first amplifying means is operating in the symmetrical output mode and the second amplifying means is operating in the asymmetrical mode. 4. LF amplifier for use in a tuner according to claim 2 or 3. 5. Mixer oscillator integrated circuit comprising an LF amplifier according to claim 3.

Inventors: CRAND OLIVIER, WINK MEYE, CRAND, OLIVIER, WINK, MEYE
Applicants: KONINKL PHILIPS ELECTRONICS NV, KONINKLIJKE PHILIPS ELECTRONICS N.V.
Application year: 1999
Main classification: H03F3
IPC codes: H03F3, H04B1