High frequency broadband push-pull power amplifier

 

(57) Abstract:

In the high-frequency broadband push-pull power amplifier with two power amplifier (1), balancing transformer (3), connecting cable (6) and switchable poddiapazona the harmonic filters (8) used a lowpass filter (LPF) with a cutoff frequency above the operating frequency of the amplifier (1). The first capacitor (2) low-pass filter is installed at the inlet of balancing transformer (3). Series inductance (4) and parallel input connection cable capacitor (5) low-pass filter included in the unbalanced circuit between balancing transformer (3) and connecting cable (6). Effect: increased efficiency and linearity. 1 Il.

The invention relates to electrical engineering and can be used in high-frequency broadband push-pull power amplifiers included in a transmitting devices.

For the transmission of high frequency signals are broadband push-pull power amplifiers with suppression of even harmonics), the output signal of which is transmitted through the switchable harmonic filters for the transmission signal with an operating frequency and singing efficiency push-pull high frequency wideband power amplifiers, working usually in the nonlinear regime (class B or AB), it is necessary to form an active load resistance of the first harmonic (f0and low reactance for odd harmonics (3f0, 5f0) of the transmitted signal [P1, P2]. This problem has various solutions.

Known push-pull amplifiers [H1, page 115], in which the output circuits contain l-shaped forming contours (CFORMS, LFORMS) installed on the outputs of the amplifiers push-pull stage. The presence of two shaping circuits in push-pull amplifier does not allow for the same load resistance for each transistor (due to the deviation of the capacitance and inductance of the nominal value), complicates the design of l-shaped forming contours in low impedance circuits and leads to instability of the amplifier when operating in the upper operating frequency.

In push-pull power amplifier, selected as a prototype [C2, page 106], between the collectors of the transistors in the output circuit contains a capacitor, which together with the leakage inductance of the transformer produces resonance at a frequency above the maximum itproved transformer when the destabilizing influences (temperature, moisture and so on) that will lead to changes in the load resistance for the transmitted signal and its harmonic components. In addition, the leakage inductance of the transformer depends on its design, which causes a change in capacitance between the collectors of transistors within wide limits and depends on the load reactance for harmonic components, which ultimately does not allow to realize the maximum efficiency of the power amplifier.

The aim of the present invention is to increase the efficiency and linearity of high-frequency broadband push-pull amplifier, which is loaded on a switched harmonic filter. This goal is achieved by the fact that high-frequency broadband amplifier that contains a balancing transformer, connecting cable and poddiapazona switched harmonic filters, use a lowpass filter (LPF) with a cutoff frequency above the operating frequency of the amplifier, and the first capacitor low-pass filter is installed in parallel to the output electrodes of the two-stage cascade amplifier, the input of the balancing transformer, and posledovatelnyi balancing between the transformer and the connection cable.

For the transmitted signal setting LPF with a cutoff frequency above the operating frequency, does not have a significant impact, as the wave resistance of cables and characteristic impedance low-pass filter and filter harmonics consistent with the load resistance of the amplifier, and the standing wave ratio of the tract may be close to 1. For the harmonic components of the signal transmitted through the switchable filter harmonic of the upper frequency subband, the LPF capacitor installed at the outlet of the two-stage cascade amplifier, has a shunt effect.

For the harmonic components of the signal transmitted through the switchable filter harmonics of the lower frequency sub-bands, the main shunt effect of the equivalent input capacitance of the harmonic filter.

For the harmonic components of the signal transmitted through the switchable harmonic filter medium frequency sub-bands, the shunt effect is formed by the input capacitor LPF and transformed into a capacitive reactance through a balancing transformer reactance serially connected inductances the Oh reactivity switched harmonic filter.

The above explanation is confirmed by the following formulas for the equivalent capacity of the filter harmonics Cfevaluated through a connecting cable to LPF, - 'fand normalized conductivity matching network for harmonic components of the signal being transmitted.

< / BR>
where f is the harmonic frequency of the signal being transmitted;

l1the length of the connecting cable;

- dielectric inner cable insulation;

R - wave resistance of the cable;

C is the speed of light in space.

< / BR>
where f1the cutoff frequency of LPF;

1,2normalized element values LPF;

l2- cable length balancing transformer;

< / BR>
Benchmarking scheme with the prototype shows that the proposed device has a different structure and compounds, therefore, it meets the criterion of "novelty". Transforming properties of long lines (cables) are widely known, however, their use in combination with elements of the low-pass filter in the high frequency broadband matching network devices to ensure transmission signal with an operating frequency and bypass the higher harmonic components of osvoennosti amplitude characteristics and efficiency of the power amplifier, it follows from this conclusion about the technical solutions according to the criterion of "significant differences".

The drawing shows a block diagram of high-frequency broadband push-pull amplifier consisting of two amplifiers 1, the first capacitor 2 LPF, balancing transformer 3, the inductance 4 low-pass filter, the second low-pass condenser 5, the connecting cable 6, two high-frequency switches 7 and harmonic filters 8.

The device operates as follows. Out-of-phase signal from the output of the amplifier 1 is fed to the condenser 2 low-pass filter and the input of the balancing transformer 3, the output of which is connected with other elements of the low-pass filter - inductor 4 and capacitor 5. Since the cutoff frequency of LPF above the upper operating frequency, the wave resistance of the cable and the characteristic impedance LPF agreed, the signal with an operating frequency is transmitted to the agreed load without weakening. Further, the signal through the connecting cable 6 with an impedance equal to the load is transmitted through the switch 7 and the filter 8 harmonics useful to the agreed load. Signal with an operating frequency from the output of push-pull amplifier 1 is transferred to the output via a connector, with the volume of the standing wave path, can be minimized by selection of component values.

Odd harmonic components of the signal being transmitted through the filter harmonic of the upper frequency subband are bridged by condenser 2 LPF. Suppression of even harmonics of the transmitted signal is the typical circuit of push-pull amplifier.

Odd harmonic components of the signal being transmitted through the harmonic filter medium frequency subband are bridged with a total capacity of condenser 2 LPF and transformed into the capacity of the balancing transformer 3 series-connected inductor 5 and capacitor 5 LPF with regard to reactivity, transformed connecting cable 6, the equivalent input capacitance of the harmonic filter 8.

Odd harmonic components of the signal transmitted through the filter of 8 harmonics of the lower frequency sub-bands, are bridged equivalent input capacitance of the harmonic filter 8. The choice of cable lengths balancing transformer 3 and the connecting cable 6 should be made so that the equivalent load capacity for odd harmonics of the signal transmitted through the filter of 8 harmonics of each frequency subband, oezil of 8 harmonics of the lower frequency sub-bands are bridged equivalent input capacitance of the harmonic filter 8.

Due to the shunting effects of the equivalent load capacitance for odd harmonics form a voltage on the output electrodes of the push-pull amplifier is sinusoidal in nature, and each amplifier 1 operates in nemonapride mode, and the operating point does not fall within the scope of the critical line mode even when the maximum delivered power that determines the linearity of the amplitude characteristic of the amplifier. Shunt capacitive load reactance for odd harmonic components of the transmitted signal does not cause the increase of the pulse current of the transistor. The current consumption of the transistor is proportional only to the current of the first harmonic, the power of which is allocated to the payload, thereby increasing the efficiency of the amplifier.

Formulas allow you to select the optimum component values LPF, harmonic filters, the length of the connecting cable and the cable length balancing transformer. Positive experimental results are confirmed by calculations. The efficiency of the considered amplifier is not less than 50% over the entire operating frequency range when the degree of suppression of intermodulation products greater or equal to minus 33 dB, which is higher than the other Century Shahgeldyan. M.: Radio and communication, 1993, S. 115.

2. RED. E. reference manual for high frequency circuitry. - M.: Mir, 1990, S. 106.

High frequency broadband amplifier that contains a push-pull amplifier stage, balancing transformer, connecting cable and switched poddiapazona the harmonic filters and, wherein, the signal amplification cascade is transmitted to the connecting cable and switched poddiapazona the harmonic filters through the lowpass filter (LPF) with a cutoff frequency above the operating frequency of the amplifier, and the first capacitor low-pass filter is installed in parallel to the output electrodes of the amplifier at the input of balancing transformer and series inductance and parallel input connection cable capacitor low-pass filter included in the unbalanced circuit between balancing transformer and connecting cable.

 

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