TDC

We use AS6501 TDC(Time to Digital Converter) chip to convert arriving time of q-bit to digital data. All modules and IP manage in/out signals from TDC are grouped under block tdc:

clk_rst_buffer

tdc_olvds.v: buffer for differential output signals, clocks

tdc_ilvds.v: buffer for differential input signals,clocks

tdc_clk_rst_mngt.v : generate refclk 5MHz, rstindex for TDC; generate simulated STOPA signal for TDC

• User parameters of tdc_clk_rst_mngt

time_spi

Quad AXI spi: IP of AMD, manage to transfer data from AXI bus to spi bus. All information of IP is provided by Xilinx

spi_inout_mngt.v: mananage inout pins from quad AXI spi to physical spi pins

system_ila_tdc

ILA debug core, probes signals under tdc blocks

tdc_mngt

tdc_core.v:

Manages digital data from TDC, output tdc time/global counter/click result depends on axil commands.

tdc_reg_mngt.v:

Manages axilite registers.

User parameters: |Parameter |Value |Description |--------------------|------|------------ |C_S_Axil_Addr_Width |12 |Address width of axil interface |C_S_Axil_Data_Width |32 |Address width of axil interface

Port descriptions

fifo_gc_tdc_rtl.v:

Instantiates fifo_gc_tdc, this fifo is axistream fifo. Instantiate axistream fifo in an RTL module allows to modify FREQ_HZ parameter of axistream interface when rebuild the block design.

Axil registers

• Base address: 0x0000_0000
• Offset address slv_reg(n) : 4*n

slv_reg0 - R/W Access - Trigger Control

slv_reg1 - R/W Access - Configuration

slv_reg2 - R/W Access - Trigger Control

slv_reg3 - R/W Access - Configuration

It depends on frequency of STOPA(in tdc_clk_rst_mngt.v) to set limit high and limit low for duty cycle. The limit value is in unit of clk200 period

slv_reg4 - R/W Access - Configuration

• Qubit rate is 80MHz(12.5ns)
• TDC resolution is 20ps
• Gate position should be in range 0..625

slv_reg5 - R/W Access - Configuration

slv_reg6 - R/W Access - Configuration

slv_reg7 - R/W Access - Configuration

slv_reg8 - R/W Access - Configuration

slv_reg9 - R/W Access - Trigger Control

slv_reg10 - R/W Access - Trigger Control

slv_reg14 - R Access - Monitoring

slv_reg15 - R Access - Monitoring

slv_reg16 - R Access - Monitoring

Data flow

Picture below shows an overview how data flows through modules and xdma channels. Responses to commands are written in modules tdc_core.v

Software control functions

Setting registers used in state machine under clk200

def Time_Calib_Reg(command,t0, gc_back, gate0, width0, gate1, width1):
    BaseAddr = 0x00000000
    Write(BaseAddr + 16,hex(int(width0<<24 | gate0))) #gate0
    Write(BaseAddr + 20,hex(int(width1<<24 | gate1))) #gate1
    Write(BaseAddr + 24,hex(int(t0))) #shift tdc time = 0
    Write(BaseAddr + 28,hex(int(gc_back))) #shift gc back = 0
    Write(BaseAddr + 32,hex(int(command))) #command = 1: raw | =2: with gate
    Write(BaseAddr + 36,0x0)
    Write(BaseAddr + 36,0x2)# turn bit[1] to high to enable register setting

Initialize tdc module, global counter in tdc module is local, it means it's available in Bob only for calibration purpose. There are 2 state machines in tdc module:

• state machine under lclk_i: Config_Tdc() sets registers and enable this state machine, output digital data in FPGA
• state machine under clk200: Reset_gc() and Start_gc() send command to reset and start global counter

def Time_Calib_Init():
    Config_Tdc() #Get digital data from TDC chip
    Reset_gc() #Reset global counter
    Start_gc() #Global counter start counting at the next PPS

Get detection result, function Get_Stream() includes reset fifo_gc_tdc and read data from xdma0_c2h_*.

def Cont_Det(): 
    num_data = 2000
    Get_Stream(0x00000000+40,'/dev/xdma0_c2h_2','data/tdc/output_dp.bin',num_data)
    command ="test_tdc/tdc_bin2txt data/tdc/output_dp.bin data/tdc/histogram_dp.txt"
    s = subprocess.check_call(command, shell = True)

    time_gc = np.loadtxt("data/tdc/histogram_dp.txt",usecols=(1,2),unpack=True)
    int_time_gc = time_gc.astype(np.int64)
    duration = (max(int_time_gc[1])-min(int_time_gc[1]))*25
    click_rate = np.around(num_data/(duration*0.000000001),decimals=4)
    print("Number of count: ", str(len(int_time_gc[1])))
    print("Appro click rate: ", str(click_rate), "click/s")