CFFT AND RFFT using CMSIS DSP library

Hi,

I am currently trying to use the CMSIS DSP library for finding the frequency bin. I have used both  CFFT and RFFT function to compute the frequency bin of input signal.

My input data is of 128 samples which content only real part (complex part is zero).

By using CFFT i'm getting accurate results but if i use RFFT function i'm seeing noise content in the spectrum.

By using RFFT ,the spectrum looks as shown in below figure ,Second figure represents the spectrum of input signal by  CFFT function

I have used CFFT and RFFT function in my project as shown below

#ifdef USE_CFFT

           for(i = 0 ; i < 2*FFT_POINTS ; i++)

            {

                        fft_testInput1[i*2] = Inputdata[i];

                        fft_testInput1[(i*2)+1] = 0x0;

            };

         /* Initialize the CFFT/CIFFT module */

         arm_cfft_radix2_init_f32(&S, 128, 0, 1);

         /* Process the data through the CFFT/CIFFT module */

          arm_cfft_radix2_f32(&S, fft_testInput1);

#else

  /* Initialize the RFFT module */

  arm_rfft_init_f32(&rS , &S_Cr, 128 ,0, 1);

/* Process the data through the RFFT/RIFFT module */

  arm_rfft_f32(&rS,Chebwin_Output,fft_testOutput);

#endif

My question is,By using RFFT Spectrum i'm seeing noise in the spectrum.why i'm seeing noise in RFFT case ?

If i'm wrong in using functions means please correct me.

Thanks in advance.

Jineshwar Nyamagoud