Abstract: A variable gain amplifier includes a source-grounded transistor, to a gate of which an input signal is supplied; a plurality of first cascode transistors, sources of which are connected to a drain of the source-grounded transistor; a second cascode transistor, a source of which is connected to the drain of the source-grounded transistor; a first gate-grounded transistor, a source of which is connected to drains of the plurality of first cascode transistors, and to a gate of which a constant voltage is applied; and an output load connected to a drain of the first gate-grounded transistor wherein the plurality of first cascode transistors and the second cascade transistor are put into a conducting state or a non-conducting state such that a drain current of the source-grounded transistor is constant and moreover a fraction of the drain current supplied to the plurality of first cascade transistors changes.

Abstract: A variable gain amplifier includes a source-grounded transistor, to a gate of which an input signal is supplied; a plurality of first cascode transistors, sources of which are connected to a drain of the source-grounded transistor; a second cascode transistor, a source of which is connected to the drain of the source-grounded transistor; a first gate-grounded transistor, a source of which is connected to drains of the plurality of first cascode transistors, and to a gate of which a constant voltage is applied; and an output load connected to a drain of the first gate-grounded transistor wherein the plurality of first cascode transistors and the second cascade transistor are put into a conducting state or a non-conducting state such that a drain current of the source-grounded transistor is constant and moreover a fraction of the drain current supplied to the plurality of first cascade transistors changes.

Abstract: A signal level monitoring circuit for outputting either voltage or current corresponding to an input signal level, includes a variable gain unit for obtaining a predetermined output level without being dependent on a gain, when the input signal level is a predetermined reference input level; and an offset adding unit for outputting a predetermined reference output level by adding an offset level to the output level of the variable gain means, when the input signal level is the predetermined reference input level. According to the present invention, it is possible to adjust precisely and surely the gain and the offset voltage based on simple adjusting steps in a short time and only once.

Abstract: An output level automatic control apparatus suitable for use to keep a transmitted output level of a radio system constant has an objective to prevent an output level above a specified value from being transmitted if an input level abruptly becomes a normal level from a break state, and to stabilize the output level with a simple configuration. The output level automatic control apparatus includes a main amplifier output level feed-back control loop extending from an output side of a main amplifier to a variable attenuator, which main amplifier output level feed-back control loop includes an output level detecting means, a reference value setting means, and a control means controlling the variable attenuator on the basis of a result obtained by comparing a detected output of the main amplifier with a reference value.

Abstract: Disclosed is an amplifying circuit comprising an amplifying transistor for amplifying an input signal, and a bias circuit for determining a current passing through the amplifying transistor and for determining an output voltage at the output of the amplifying transistor. The bias circuit comprising a current determining transistor for determining a current conducting through the amplifying transistor and a voltage determining transistor for determining an output voltage at the output of the amplifying transistor. The output voltage is determined independently from the determination of the current.