1. Field of the Invention
The invention concerns a programmable amplifier which can be integrated in the form of an analog ASIC (Application Specific Integrated Circuit) for amplification applications in the field of space telecommunications.
An object of the device in accordance with the invention is to enable amplification with a gain between 2.sup.n and 2.sup.n-1 in steps of 2.sup.p where p&lt;n and n is the number of gain control bits.
2. Description of the Prior Art
A conventional solution to obtaining amplification as defined hereinabove implemented in the form of an ASIC is to use an amplifier associated with a programmable attenuator such as that described in the article "Programmable attenuator" by A. A. Shakhin and A-Ya. Stul (1979, Plenum publishing corporation). However, various problems specific to integrated circuits are then encountered concerning:
accuracy of resistor values; PA1 bandwidth; PA1 switching components. PA1 bandwidth; PA1 noise factor; PA1 compression; PA1 transistor matching. PA1 a plurality of stages having two gain values selectable by a control bit, and PA1 at least two identical stages having a different control bit, PA1 each stage having a maximum gain less than 2.sup.n-1.
Resistor values are difficult to control in ASICs. The accuracy that can be achieved in the absolute resistance value is around .+-.25%, compared with a possible accuracy of 1% in discrete resistors. Also, it is not possible to use capacitor values exceeding a few dozen picofarads (pF).
An alternative solution is to use a plurality of amplifiers connected in cascade; the first amplifier has a high gain to obtain the best possible signal/noise ratio. The bandwidth is then significantly reduced, however.
An object of the invention is to provide a programmable amplifier device of this kind which has very good: