A DEVICE FOR GENERATING AN AC AMPLITUDE-DEPENDENT INDICATOR

Abstract: A device for generating an indicator signal which is representative of an AC signal amplitude input to the device, the device comprising at least one semiconductor whose DC bias current is representative of said AC signal amplitude, and means for deriving the indicator signal from the DC bias current. Such a device can, for example, be used for controlling the RF power to be generated in a communication network.

Description: A device for generating an AC amplitude-dependent indicator. The present invention relates to a device for generating an indicator signal which is representative of an AC signal amplitude input to the device. The present invention also relates to the use of such an indicator signal, to a base station, a handset and to a receiver or transceiver provided with such a device and to a network including a base station and handset according to the claims 7, 8, 9, 10 and 11 respectively. Such a device is known from our European patent application EP-A-0 152 985. The device disclosed therein is a high-frequency amplifier arrangement for generating an indicator signal which is representative of an AC signal amplitude in the device. For the known device to generate an indicator signal which is used to control the gain in amplifier stages in the device an, IF signal on input S is being AM detected to reveal the automatic gain control (AGC) indicator signal. The AGC uses a broadband AM detector to cope with the full frequency range of the AC signal. To achieve that goal, the known device is not a low power consuming device and is therefore not suitable for application in an environment where a low power consumption is required such as in portable or mobile devices, such as telephones, base stations, handsets, and pagers. It is an object of the present invention to provide a low power consuming device over a broad frequency range, which device is capable of being used as an RSSI (Received Signal Strength Indicator), such as in AGC. Thereto the device according to the present invention is characterized in that the device comprises at least one semiconductor whose DC bias current is representative ofsaid AC signal amplitude, and means for deriving the indicator signal from the DC bias current. A low DC bias current flows through the semiconductor if a zero AC signal amplitude is input and the DC bias current is related to the input AC signal amplitude. This reduces the power consumption of the device according to the present invention as no DC current is spilt. It is a further advantage of the device according to the invention that the means for deriving the indicator signal can be embodied as averaging or low-pass means which are both simple and require little power. In addition it is an advantage that a variety of practical implementations embodying the principle of a DC bias current representing the AC signal amplitude can be realised. The device can advantageously be used for controlling the gain in an amplifier circuit, such as in a receiver or transceiver in a base station and/or handset in a network, such as a communication network for minimizing gain to reduce the power consumption and in particular for minimizing RF power supplied to the air in order to furthermore minimize mutual disturbance between communicating parties in the network. Further advantageous embodiments of the device according to the present invention are outlined in the dependent claims. At present the device according to the invention will be elucidated further together with its additional advantages while reference is being made to the appended drawing, wherein like components are referred to by like reference numerals. In the drawing: Fig. 1 shows a simple first embodiment of the device according to the invention for generating a received signal strength indicator (RSSI) signal , Fig. 2 shows a second embodiment of the device according to the invention having a balanced RF signal output and current mirror means, Fig. 3 shows a third embodiment of the device according to the invention embodied by a current mirror means, Fig. 4 shows a fourth embodiment of the device according to the invention, Fig. 5 shows a fifth embodiment of the device according to the invention having a semiconductor connected in the common base circuit, and Fig. 6 shows an embodiment of a block diagram of a handset comprising a receiver according to the invention wherein two devices used as received RF and IF signal strength indicator (RSSI) devices are used respectively. Figs. 1-5 show embodiments of a device 1, comprising the main stream path designated A of a semiconductor 2, such as a bipolar transistor as shown or possibly a FET, MOS-FET or another controllable semiconductor possibly adjusted in class A/B, class B, class C or even class D. The transistor 2 has a collector-emitter path forming the main DC bias current path A. The transistor 2 has a base 3 in the embodiment as shown forming a control input to which, through a capacitor 4, an AC input signal, such as an RF or an IF or LF signal having a certain amplitude or strength, is applied. The semiconductor has a curved, viz. an exponential or a quadratic control input characteristic area, as is the case with a bipolar transistor or a FET, respectively. The DC bias current of the semiconductor 2 in the figures 1-5, if adjusted in this curved area, provides for the feature that the AC signal amplitude applied thereto results in a DC bias current, which is representative ofthe AC signal amplitude of the signal on input AC. The DC bias current, if fed through a resistor 5 connected to the supply voltage V c of the device 1 , provides an AC output signal on AC 0Ut containing the DC bias component, which in turn is fed to further means RC for deriving an indicator signal RSSI from the DC bias current. In particular the means RC comprise an RC low-pass filter as shown, or possibly an LR low-pass filter (not shown) for providing the indicator voltage signal RSSI, which is representative of the AC signal amplitude input to the device 1. A low DC bias current flows through the main current path A if a zero amplitude AC signal is input. The RSSI signal may be fed back to the base 3 of the transistor 2 which is schematically shown by a controllable DC voltage source AGC. This AGC reduces the DC bias current which reduces the current consumption of the device 1 even further. Fig. 2 shows a second embodiment of the device 1, wherein the AC signal is input on an emitter 6 of a transistor 7 connected in a common base circuit, whose base 8 is connected to the AGC as explained in relation to fig. 1 and whose collector 9, being connected to V c through resistor 10, forms one terminal of a balanced AC output. The other terminal of the balanced AC output is connected to a V c coupled resistor 11 and to a collector 12 of a transistor 13, whose base 14 is connected to AC iπ and whose collector- emitter main current path is mirrored in the path A of the part of the device 1 the functioning whereof has already been described in relation to fig. 1. A third embodiment of the device 1 is shown in figure 3 where the main current in path A is now mirrored in the collector-emitter current path of a transistor 15 which DC level is again representative ofthe input AC signal magnitude passed through a transistor 16 whose collector 17 is connected to a V c resistor 18 and a further transistor 19 providing base control through two junctions D to mirrored transistors 2 and 15. Voltage source DC provides DC input adjustment of transistor 16. A fourth embodiment of the device 1 is shown in figure 4. This embodiment is also outlined and explained in relation to its functioning as an amplifier having improved large AC signal behaviour as disclosed in EP application number 97201944.2 (see figures 1 and 2 therein) filed 25 June 1997, which is incorporated here by reference. It turned out that this amplifier, if provided with mirroring transistor 2 and the low-pass means such as RC and explained hereinbefore can also be used for generating the RSSI signal now desired. Fig. 5 presents a fifth schematic basic embodiment of the device 1 wherein the transistor 2 is now connected in the common base circuit. AC is input to emitter 20 of transistor 2 through parallel coil L which prevents leakage to ground. Base 21 thereof is DC voltage controlled by voltage source DC, which is connected in series with resistor 22 in a parallel combination with capacitor 23. Collector 24 of the transistor 2 is connected to a resistor 25 and the RC means described earlier, which means in turn is connected to voltage source V. Again at output RSSI the indicator signal is generated which is representative of the input AC signal amplitude. If so required, path A could be mirrored as described earlier too. The possible use of the RSSI signal in a receiver or transceiver in a handset 26 such as used in a telephone network, is explained with reference to fig. 6. The handset 26 comprises an antenna 27 coupled to a receiving part as shown which includes an RF amplifier 28, a received RF signal strength indicator device 29, a first A/D convenor 30, a digital signal processing (DSP) circuit 31 connected to D/A convertors 32 and 33, an IF amplifier 34 connected to the RF amplifier 28, a received IF signal strength indicator 35 and a second A/D convertor 36 coupled to DSP circuit 31. For achieving AGC, the D/A convertors 32 and 33 are connected to RF amplifier 28 and IF amplifier 34, respectively. The arrangement of particularly the RSSI circuits 29 and 35 allow separate RF signal and IF signal gain control for minimizing power consumption in the handset 28 and for minimizing RF power to be generated in a communication network, thus minimizing mutual disturbance between parties in the network. The IF amplifier 34 is connected to a data processing circuit 37 for outputting the desired data. In view of the foregoing it will be evident to a person skilled in the art that various modifications may be made within the spirit and the scope of the present invention as hereinafter defined by the appended claims and that the present invention is thus not limited to the examples provided.

Claims: CLAIMS: 1. A device for generating an indicator signal which is representative of an AC signal amplitude input to the device, characterized in that the device comprises at least one semiconductor whose DC bias current is representative of said AC signal amplimde, and means for deriving the indicator signal from the DC bias current. 2. The device according to claim 1, characterized in that the semiconductor has a control input and an area where the control input characteristic is curved, whereby the device is embodied to bias the semiconductor in said area. 3. The device according to claim 1 or 2, characterized in that the semiconductor is embodied as a class A/B, class C and/or class D biased semiconductor. 4. The device according to one of the claims 1-3, characterized in that the semiconductor is connected in the common base circuit, the common emitter circuit, the common gate circuit, the common source circuit or the common drain circuit. 5. The device according to one of the claims 1-4, characterized in that the device is provided with at least a current mirror means for mirroring said DC bias current. 6. The device according to one of the claims 1-5, characterized in that the device includes automatic gain control means having a control input to which the indicator signal is applied. 7. Use of an indicator signal generated by a device according to one of the claims 1-6 for controlling the gain in an amplifier circuit, such as an LF, IF and/or RF amplifier circuit and/or for controlling the RF power to be generated in a communication network, such as a telephone network for communication between one or more base stations and handsets. 8. A base station including a device according to one of the claims 1-6 for generating an indicator signal which is representative of an AC signal amplitude input to the device, characterized in that the device comprises at least one semiconductor whose DC bias current is representative ofsaid AC signal amplitude, and means for deriving the indicator signal from the DC bias current. 9. A handset including a device according to one of the claims 1-6 for generating an indicator signal which is representative of an AC signal amplimde input to the device, characterized in that the device comprises at least one semiconductor whose DC bias current is representative of said AC signal amplitude, and means for deriving the indicator signal from the DC bias current. 10. A network comprising at least one base station according to claim 8 and at least one handset according to claim 9, each including a device according to one of the claims 1-6 for generating an indicator signal which is representative of an AC signal amplimde input to the device, characterized in that the device comprises at least one semiconductor whose DC bias current is representative of said AC signal amplimde, and means for deriving the indicator signal from the DC bias current. 11. A receiver or transceiver including a device according to one of the claims 1-6 for generating an indicator signal which is representative ofan AC signal amplimde input to the device, characterized in that the device comprises at least one semiconductor whose DC bias current is representative of said AC signal amplimde, and means for deriving the indicator signal from the DC bias current.

Inventors: WAGEMANS ANTONIUS G, WAGEMANS, ANTONIUS, G.
Applicants: KONINKL PHILIPS ELECTRONICS NV, PHILIPS SVENSKA AB, KONINKLIJKE PHILIPS ELECTRONICS N.V., PHILIPS AB
Application year: 1999
Main classification: H03G3
IPC codes: H03G3, H04B1