Introduces a new temperature compensated crystal oscillator - AMCXO, a MCXO based on an analogue approach - and compares the performance differences between MCXO and AMCXO and analyses the necessity to develop AMCXO. Combined with their test systems AMCXO and MCXO are both based on computer to generate the control signals to the compensated crystal oscillators according to temperature variation. However, in the practical temperature compensated crystal oscillators the execution devices are much different to each other. MCXO uses a set of digital units including a microprocessor to complete the compensation. In it equations or tables are used to express the relationship between the control signal and temperature. AMCXO uses an analogue memory, which has the same functions as the digital units of MCXO. In AMCXO a curve or figure based on the equations or table is used to express the same relationship. Now AMCXO is mainly based on AT cut crystals. Therefore, in this paper we only compared it with the MCXO based on AT cut crystals.