Patent ID: 6268734
Filing Date: 2001-07-31
Classification: G01R,H03F

Abstract:
An operational amplifier test circuit, comprising:an operational amplifier (op amp) having an input offset voltage (VOS), inverting and non-inverting inputs having respective input bias (IB) currents, and an output,a first resistance connected between said inverting input and a ground point,a second resistance connected between said non-inverting input and said ground point,a feedback circuit connected between said output and one of said inputs which establishes a gain value for said test circuit such that the VOS of said op amp is equal to said op amp's output divided by said gain value,at least one current measuring means switchably inserted into said test circuit between said first resistance and said inverting input or between said second resistance and said non-inverting input,at least one set of latching relay contacts connected across a respective one of said current measuring means which when closed provides a low resistance path around its respective current measuring means to enable said op amp's VOS to be measured and when open inserts said current measuring means into said test circuit to enable the IS of the op amp input to which it is connected to be determined, andelectrical operating means for operating said at least one set of latching relay contacts in response to a set of control signals, said operating means comprising electromagnetic coils to latch said sets of latching relay contacts open and closed, said coils becoming heated when operated, said latching relay contacts and electrical operating means enabling the use of a short duty cycle to operate said coils such that thermal electromotive force (E.M.F.) that would otherwise be in series with said sets of contacts due to the heating of said coils is substantially eliminated.