Modern cellular base stations are becoming increasingly multi-carrier and multi-standard/multi-mode for improved efficiency and manageability. Primary among prospective multi-mode base station deployments will be those that are reconfigurable but also capable of simultaneous transmission of several types of cellular signals. However, unified or convergent-transmitter design is challenging, particularly with the small specified tolerances for signal distortion. We present an analysis of the Error Vector Magnitude (EVM) specifications for GSM/EDGE, UMTS and LTE, based on simulated EVM sensitivity to various distortions, focusing on a convergent transmit chain for multi-standard, multi-carrier macro-cell base stations. These analyses illustrate a method of deriving preliminary radio transmitter performance (phase noise, IQ imbalances, noise floor etc.) requirements, alongside helping to expose bottlenecks and performance tradeoffs necessary to optimize power consumption. A preliminary distribution of distortion or performance among the blocks is presented, to achieve the less than 5% multi-mode EVM budget, for worst-case scenarios.