# how to design sigma(std) vector to have values above > 0 in VAE autoencoder

I am trying to understand how to design mu and sigma vector in VAE autoencoder, as we know std value can not be larger than 0. If I use linear function, the value can be lower than zero, so I think Relu is the only activation function to apply in order to get sigma (Std) vector larger than zero. Would this be correct understanding?

$$\sigma = \exp(\rho)$$
where $$\rho$$ is coming from the encoder.