Circuit for controlling the output amplitude of a high frequency power amplifier

p0001The invention relates to an arrangement for regulating the output amplitude of a high frequency power amplifier according to the preamble of claim 1.

p0002The invention finds application in, for example, a temperature compensation for power amplifier with a peak power of about 10 watts for the GHz range (X-band; 8 GHz to 12 GHz). However, the invention is not limited to this frequency band, and this performance class.

p0003Such power amplifiers are needed, for example in radar technology as a transmission amplifier in transmit / receive modules (T / R) modules for phased array antennas. In such a T / R modules, the output of the power amplifier is generally directly, in particular without phase and / or amplitude control element, a (transmit) fed radiating element. For a pivoting and / or shaping of the transmit radiation pattern of such an antenna, it is necessary that as closely as possible predetermined phase and amplitude conditions are observed between the light emitted by adjacent radiator elements waves. a plurality, for example, a few thousand, such T / R modules are now at such an antenna used as a high measurement, calibration and adjustment expenses in an opaque manner required to adjust the required phase and / or amplitude of use and / or to check. Aussderdem the necessary measurement and adjustment (components) must be present at each T / R module disadvantageously. These are disadvantageously among other susceptible itself and not cost-effective.

p0004The invention is therefore based on the object to provide a generic arrangement, with the precise control of the output amplitude of a power amplifier is possible and that is spatially small, mechanically robust, reliable, and inexpensive to produce, especially in an industrial scale production.

p0005This object is achieved by the features specified in the characterizing part of patent claim 1. Advantageous embodiments and / or refinements are the further claims.

p0006A first advantage of the invention is that the arrangement is completely for microwave applications, executable in semiconductor technology, particularly in GaAs technology.

p0007A second advantage is that even amplitude changes that arise due to temperature change (temperature drift) in the power amplifier is detected and corrected (compensated) will be.

p0008A third advantage is that the arrangement has a high efficiency. That is, it is produced additionally by the rules at most a negligible amount of heat loss. High efficiency is particularly advantageous if a plurality of power amplifiers are substantially simultaneously operated, for example, in the T / R modules of a phased array antenna mentioned above.

p0009Further advantages result from the following description.

p0010The invention is explained in more detail below with reference to embodiments with reference to schematically illustrated figures. Show it<dl id="dl0001" compact="compact"><dt>FIG. 1</dt><dd>an example shown schematically</dd><dt>FIG. 2</dt><dd>an arrangement previously used</dd><dt>FIG. 3, FIG. 4</dt><dd>more schematically dargestelle examples to illustrate the invention.</dd></dl>

p0011The invention is based on an amplifier arrangement, in particular, as a power amplifier (transmission amplifier) ​​for the microwave wavelength range, for example the range of 8 GHz to 12 GHz (X-band), are suitable. When such amplifiers in T / R modules, a phased array antenna is used, the amplifier over in the largest possible temperature range (operating range) should have the highest possible amplitude accuracy, ie, a predetermined power gain should be in the area to be as small as possible (narrow) exhibit tolerance range. A predetermined amplitude accuracy can be achieved by means of a dependent control circuit for controlling the output power of the amplifier. Is this designed as a so-called linear power amplifier, so that legislation can be done for example by means of an amplitude control element at the RF input of the amplifier.

p0012In particular, in an application in T / R modules, it has proved advantageous to use so-called saturated power amplifier. These preferably operate at the maximum possible (RF) power. This is then only dependent on the selected operating voltage and / or the chosen operating current. For controlling the output power (output amplitude) of such saturated power amplifier is therefore a regulation of the operating voltage and / or the operating current depending on the output amplitude is required.

p0013FIG. 2 shows such a saturated power amplifier with a regulation of the operating voltage as a function of the output amplitude. The power amplifier consists for example of two field effect transistors T1, T2, where in each case both the gate terminals G1, G2 and, respectively, the drain terminals D1, D2 are connected in parallel to a common gate terminal G and a common drain terminal D. to be amplified input signal, such as a radar transmission signal passes through the amplifier input VE, an input coupling arrangement EK, with input completion EA (RF sump), at the field-effect transistors T1, T2, where it is amplified and passes through a output switch assembly AK, with output termination AA (RF swamp) to the amplifier output VA. This is connected to a T / R module substantially over a transmit / receive switch to a transmit / receive antenna element.

p0014To control the output power (output amplitude) a predetermined percentage, for example, about -20 dB, the output signal will be at the amplifier output VA via a coupler RK, with completion KA (RF swamp) coupled and rectified in a peak detector PD. At the output of which is produced essentially a low-frequency measurement signal (controlled variable) with a DC voltage component. The measurement signal corresponds to the amplitude of the output signal at the amplifier output VA. This measuring signal is a drain control circuit DBC supplied, which is arranged between the common drain D and a (unregulated) drain voltage / Power supply DS. At the terminal labeled GS a gate voltage can be applied to adjust the operating point of the transistors T1, T2.

p0015It can be seen that with such an arrangement in a disadvantageous manner in the drain control circuit DBC a non-negligible power loss occurs, otherwise no control is possible. This power dissipation (heat) disadvantageously requires a technically complicated cooling arrangement and also causes a small transmitter efficiency.

p0016FIG. 1 shows an inventive embodiment, wherein only a high amplitude accuracy a high transmitter efficiency (negligible (heat) dissipation) is achieved. The illustrated arrangement can still be used advantageously for pulsed transmitters which are currently common in radar technology, especially in T / R modules. The arrangement differs from that according to FIG. 2 essentially in that the substantially unregulated (or at most low regulated) power supply voltage DS lies directly against the common drain D. The required regulation of the output power (output amplitude) occurs ensprechend FIG. 1 substantially (losses) without power via a gate control voltage, which is supplied to the common gate terminal G of the transistors T1, T2, and thereby affect the drain current of the transistors T1, T2.

p0017To generate the gate control voltage at the amplifier output VA a definable portion of the output of a coupler RK, for example, a 20dB coupler, coupled and a voltage doubler circuit PD ( "Peak Detector") rectified. This produces a DC voltage which corresponds to approximately twice the peak voltage in the example shown here, which is present at the amplifier output VA. This DC voltage is used as a control variable and fed to a (gate) control circuit GBC. There, a desired-actual value comparison of the controlled variable with a predetermined reference variable occurs (target voltage). The comparison with the resultant control deviation is required, increasingly so matched to the operating parameters of the transistors used T1, T2 and supplied to the common gate terminal G. This control loop is based on the FIG. 3, FIG. 4 in more detail explained.

p0018FIG. 3 shows the circuit diagram of a voltage doubler circuit PD. In this case, the signal present at input E RF signal via a coupling capacitor KO a rectifier consisting of diodes D1, D2, respectively. The resulting DC voltage (controlled variable) is smoothed by means of a storage capacitor SK (low-pass). Its size (capacity) depends on the required time constant of the control loop, which is a skilled worker. In addition, the capacity can be selected such that even in pulsed transmission mode (pulsed transmitter) almost independent of the pulse duration has a substantially constant controlled variable ensteht at the output A of the voltage doubler.

p0019This control variable is now the (gate) control circuit GBC (FIG. 1) supplied. This is according to the required control characteristics very different executable, such as a P controller (proportional controller) according to FIG. 4 using an operational amplifier.

p0020According to FIG. 4, the controlled variable RG is compared at the input of the operational amplifier OV with a reference variable FG, for example, an adjustable, well stabilized (reference) voltage. This comparison is made in the manner shown by means of an adder AD, or alternatively by means of the differential inputs of the operational amplifier. At the output of the adder AD ensteht one of the control deviation corresponding voltage which is amplified in the operational amplifier OV and then supplied to one input of a Umkehraddierers UA. The other input is supplied with a gate voltage command GSO for setting the operating point of the transistors T1, T2 (FIG. 1). The voltage generated at the output of GR Umkehraddierers UA is fed to the common gate terminal G (FIG. 1).

p0021With such an arrangement, wherein the adder AD, UA are designed as an operational amplifier, for example in a temperature range of about - 40 ° C to + 60 ° C (233 K to 333 K) at the output of an amplitude accuracy of ± 0.15dB accessible. Without regulation is within this temperature range on the other hand, only an amplitude accuracy of ± 0.6dB available.

p0022The invention is not limited to the disclosed embodiments but, mutatis mutandis applicable to other, such as T / R modules in satellites, where high efficiency and high amplitude accuracy is also required in a wide temperature range.

p0023In addition, the invention is not limited to the use of field effect transistors (FETs) as radio frequency (RF) is - power amplifier is limited, but for all RF amplifier elements are suitable in principle that at least one RF input, an RF output, a DC voltage Verso TION terminal and a own control voltage terminal. Such RF amplifier elements are for example cathode ray tubes, so-called dual-gate FETs, and HBTs. It is not necessary that the direct and / or control voltage connections and the RF input and RF output ports are geometrically separated.

p0024Further applications of regulated RF amplifiers are for example in the field of measuring technology, are also on which high-precision RF amplifiers required, and in all applications where a compensation of (transistor) manufacturing tolerances required.