Linear RF power amplifier

• US 5,477,188 A
• Filed: 07/14/1994
• Issued: 12/19/1995
• Est. Priority Date: 07/14/1994
• Status: Expired due to Term

• Current Assignee: MKS Instruments Incorporated
• Original Assignee: Eni SPA (Eni Petroleum Company Incorporated)
• Inventors: Chawla, Yogendra K., Reyzelman, Leonid
• Primary Examiner(s): MOTTOLA, STEVEN J
• Application Number:
  US08/275,124
• Time in Patent Office: 523 Days
• Field of Search: 330/65, 330/66, 330/67, 330/68, 330/264, 330/266, 330/269, 330/272, 330/285, 330/289
• US Class Current: 330/269
• CPC Class Codes: H03F 1/301 in MOSFET amplifiers H03F1/303, H03F1/305, H03F1/308 take precedence
• CPC Class Codes: H03F 3/193 with field-effect devices H03F3/195 takes precedence
• CPC Class Codes: H03F 3/211 using a combination of several amplifiers H03F3/60 takes precedence
• CPC Class Codes: H03F 3/265 with field-effect transistors only
• CPC Class Codes: H03F 3/604 using FET's

Abstract

A linear RF power amplifier employs push-pull pairs of high voltage mosfets. A minimum of transformers is employed, with an impedance matching transformer feeding an input balun supplying the input signal in push-pull to the gates of the mosfets. The drains are coupled to balanced legs of an output balun, followed by an output impedance matching transformer. Thermal sensors are employed for control of gate bias and also for control of drain voltage. The temperature sensors are mounted in the air inlet path and on the spreader plate of the heat sink. An aluminum or fiberglass strap is used to press the transistors against the spreader plate thereby ensuring good thermal contact with the transistor dies.

Claims

1. A push-pull RF power amplifier that comprises first and second high voltage field effect transistors each of which has a semiconductor die region contained at a predetermined location within a heat transmitting base;

a heat conducting spreader plate on which said first and second transistor are mounted in heat transfer relation;

a strap attached onto said spreader plate and sandwiching said first and second transistors between said strap and said plate, said strap being superposed over the locations of said semiconductor die regions;

a temperature sensor mounted on said spreader plate at a position between said transistors; and

bias means coupled to said temperature sensor for adjusting a voltage applied to said transistors in accordance with changes in temperature detected by said temperature sensor.

2. A push-pull RF power amplifier according to claim 1 further comprising first and second screws for mechanically holding said strap to said spreader plate.

3. A push-pull RF power amplifier that comprises first and second high power field effect transistors each of which has a source, a drain, and a gate;

a supply of drain voltage coupled to the drains of said transistors;

a signal input circuit for applying an input signal in push pull to the gates of said transistors;

an output circuit coupled to the drains of the said transistors for carrying amplified RF signal to an RF output;

a temperature sensor device held in thermal communication with said transistors and developing an output dc level that is a function of a temperature detected by said temperature sensor device;

first and second bias stabilization circuits having gate bias inputs coupled respectively to receive the output level of said temperature sensor device and respective gate bias outputs; and

first and second circuit means respectively coupling said gate bias outputs to the gates of said first and second transistors;

said first and second gate bias stabilization circuit each include means for generating a gating pulse signal, an operational amplifier having an input coupled to said temperature sensor device, and an output providing said bias level; and

a latch circuit having inputs connected respectively to said operational amplifier output and to said means for generating said gating pulse signal and an output coupled to the gate of the respective transistor.

5. A push-pull RF amplifier according to claim 3 wherein said gain stability compensation circuit includes means for measuring ambient inlet air temperature, a differential circuit providing a difference signal and having inputs coupled to said means for measuring ambient temperature and to said temperature sensor device, and output circuit means supplied with said difference signal for providing said gain adjustment signal.

6. A push-pull RF amplifier according to claim 5 wherein said gain stability compensation circuit further includes power integration means for generating an integration signal representing a time integral of amplifier output power for a predetermined time;

and said output circuit means includes means for combining said difference signal and said integration signal.

7. A push-pull RF amplifier according to claim 6 wherein said gain stability compensation circuit further includes a summing circuit that provides a sum of temperature differences, T_HTSK - T_AMB, a time integral of forward power, and a voltage to account for offset.

8. A push-pull RF amplifier according to claim 7 wherein said gain stability compensation circuit further includes a summing network having inputs for receiving output voltage from said summing circuit, and a fixed reference voltage, the output of said summing network providing a reference voltage for an error amplifier of a drain voltage power supply.

4. A push-pull RF power amplifier that comprises first and second high voltage field effect transistors each of which has a drain serving as output, and a gate, a supply of drain voltage coupled to the drains of said transistors;

a signal input circuit for applying an input signal in push-pull to the gates of said transistors;

an output circuit coupled to the drains of said transistors for carrying an amplifier RF signal to an RF output;

a temperature sensor device in thermal communication with said transistors and having an output at which is developed a d.c. output level that varies in accordance with temperature of the transistors;

a gain stability compensation circuit coupled to the output of said temperature sensor device for generating a gain adjustment signal; and

wherein said supply of drain voltage includes means for adjusting said drain voltage within a range in accordance with the gain adjustment signal.