|
|
Analog to Digital Converters - ADC 16-Bit, 5 MSPS PULSAR Differential ADC
- AD7961BCPZ
- Analog Devices
-
1:
$53.70
-
503In Stock
|
Mouser Part No
584-AD7961BCPZ
|
Analog Devices
|
Analog to Digital Converters - ADC 16-Bit, 5 MSPS PULSAR Differential ADC
|
|
503In Stock
|
|
|
$53.70
|
|
|
$42.16
|
|
|
$41.38
|
|
|
$40.00
|
|
|
View
|
|
|
$37.97
|
|
|
Quote
|
|
Min.: 1
Mult.: 1
Max.: 503
|
|
|
AD7961
|
SMD/SMT
|
LFCSP-32
|
16 bit
|
1 Channel
|
Serial
|
5 MS/s
|
Differential
|
SAR
|
1.8 V, 5 V
|
1.8 V, 5 V
|
95.5 dB
|
- 40 C
|
+ 85 C
|
|
Tray
|
|
|
|
Analog to Digital Converters - ADC 16-Bit, 200ksps, Serial Sampling ADC with Multiple Input Ranges
- LTC1609IG#PBF
- Analog Devices
-
1:
$49.76
-
1,268In Stock
|
Mouser Part No
584-LTC1609IG#PBF
|
Analog Devices
|
Analog to Digital Converters - ADC 16-Bit, 200ksps, Serial Sampling ADC with Multiple Input Ranges
|
|
1,268In Stock
|
|
|
$49.76
|
|
|
$40.82
|
|
|
$37.34
|
|
|
$35.65
|
|
|
View
|
|
|
$34.94
|
|
|
Quote
|
|
Min.: 1
Mult.: 1
Max.: 1,262
|
|
|
LTC1609
|
SMD/SMT
|
SSOP-28
|
16 bit
|
1 Channel
|
Serial
|
200 kS/s
|
Single-Ended
|
SAR
|
5 V
|
5 V
|
87 dB
|
- 40 C
|
+ 85 C
|
|
Tube
|
|
|
|
Analog to Digital Converters - ADC Dual-channel 18-bit 10-MSPS low-noise
- ADC3681IRSBT
- Texas Instruments
-
1:
$120.70
-
175In Stock
|
Mouser Part No
595-ADC3681IRSBT
|
Texas Instruments
|
Analog to Digital Converters - ADC Dual-channel 18-bit 10-MSPS low-noise
|
|
175In Stock
|
|
|
$120.70
|
|
|
$101.52
|
|
|
$94.44
|
|
|
$91.46
|
|
|
$88.95
|
|
Min.: 1
Mult.: 1
:
250
|
|
|
ADC3681
|
SMD/SMT
|
VQFN-40
|
18 bit
|
2 Channel
|
Serial
|
10 MS/s
|
Differential
|
|
1.75 V to 1.85 V
|
|
84.4 dBFS
|
- 40 C
|
+ 105 C
|
|
Reel, Cut Tape, MouseReel
|
|
|
|
Analog to Digital Converters - ADC 16-B, 5Msps Diff In ADC w/ Wide In Commo
- LTC2311IMSE-16#PBF
- Analog Devices
-
1:
$35.62
-
1,195In Stock
|
Mouser Part No
584-C2311IMSE-16PBF
|
Analog Devices
|
Analog to Digital Converters - ADC 16-B, 5Msps Diff In ADC w/ Wide In Commo
|
|
1,195In Stock
|
|
|
$35.62
|
|
|
$29.83
|
|
|
$27.50
|
|
|
$26.60
|
|
|
View
|
|
|
$25.34
|
|
|
Quote
|
|
Min.: 1
Mult.: 1
Max.: 1,195
|
|
|
LTC2311-16
|
SMD/SMT
|
MSOP-16
|
16 bit
|
1 Channel
|
Serial
|
5 MS/s
|
Differential/Pseudo-Differential
|
SAR
|
3.3 V, 5 V
|
|
|
- 40 C
|
+ 125 C
|
|
Tube
|
|
|
|
Analog to Digital Converters - ADC 18-B, 10Msps SAR ADC
- LTC2386CUH-18#PBF
- Analog Devices
-
1:
$62.91
-
513In Stock
|
Mouser Part No
584-LTC2386CUH-18PBF
|
Analog Devices
|
Analog to Digital Converters - ADC 18-B, 10Msps SAR ADC
|
|
513In Stock
|
|
|
$62.91
|
|
|
$54.21
|
|
|
$49.32
|
|
|
$48.04
|
|
Min.: 1
Mult.: 1
Max.: 513
|
|
|
LTC2386-18
|
SMD/SMT
|
QFN-32
|
18 bit
|
1 Channel
|
Serial
|
10 MS/s
|
Differential
|
SAR
|
2.5 V, 5 V
|
2.5 V, 5 V
|
96.2 dB
|
0 C
|
+ 70 C
|
|
Tube
|
|
|
|
Analog to Digital Converters - ADC 24-B Diff DS ADC w/ Sel Speed/R
- LTC2440CGN#PBF
- Analog Devices
-
1:
$19.03
-
8,811In Stock
|
Mouser Part No
584-LTC2440CGN#PBF
|
Analog Devices
|
Analog to Digital Converters - ADC 24-B Diff DS ADC w/ Sel Speed/R
|
|
8,811In Stock
|
|
|
$19.03
|
|
|
$15.14
|
|
|
$14.18
|
|
|
$13.11
|
|
|
View
|
|
|
$12.51
|
|
|
$12.29
|
|
Min.: 1
Mult.: 1
Max.: 8,811
|
|
|
LTC2440
|
SMD/SMT
|
SSOP-16
|
24 bit
|
1 Channel
|
Serial
|
4 kS/s
|
Differential
|
Sigma-Delta
|
4.5 V to 5.5 V
|
4.5 V to 5.5 V
|
|
0 C
|
+ 70 C
|
|
Tube
|
|
|
|
Analog to Digital Converters - ADC 1B 20MHz 2nd Order I so Delta-Sigma Mod A 595-AMC1204BDW
- AMC1204BDWR
- Texas Instruments
-
1:
$8.58
-
8,749In Stock
|
Mouser Part No
595-AMC1204BDWR
|
Texas Instruments
|
Analog to Digital Converters - ADC 1B 20MHz 2nd Order I so Delta-Sigma Mod A 595-AMC1204BDW
|
|
8,749In Stock
|
|
|
$8.58
|
|
|
$6.66
|
|
|
$6.18
|
|
|
$5.64
|
|
|
View
|
|
|
$4.69
|
|
|
$5.40
|
|
|
$5.25
|
|
|
$5.11
|
|
|
$4.69
|
|
Min.: 1
Mult.: 1
:
2,000
|
|
|
AMC1204
|
SMD/SMT
|
SOIC-16
|
16 bit
|
1 Channel
|
Serial
|
78 kS/s
|
Differential
|
Sigma-Delta
|
4.5 V to 5.5 V
|
3 V to 5.5 V
|
84 dB
|
- 40 C
|
+ 125 C
|
|
Reel, Cut Tape, MouseReel
|
|
|
|
Analog to Digital Converters - ADC 2.35V-5.25V 10 Bit 1 .25MSPS Serial A 59 A 595-ADS7887SDBVT
- ADS7887SDBVR
- Texas Instruments
-
1:
$4.08
-
721In Stock
|
Mouser Part No
595-ADS7887SDBVR
|
Texas Instruments
|
Analog to Digital Converters - ADC 2.35V-5.25V 10 Bit 1 .25MSPS Serial A 59 A 595-ADS7887SDBVT
|
|
721In Stock
|
|
|
$4.08
|
|
|
$3.09
|
|
|
$2.84
|
|
|
$2.57
|
|
|
View
|
|
|
$2.20
|
|
|
$2.44
|
|
|
$2.42
|
|
|
$2.28
|
|
|
$2.20
|
|
Min.: 1
Mult.: 1
:
3,000
|
|
|
ADS7887
|
SMD/SMT
|
SOT-23-6
|
10 bit
|
1 Channel
|
Serial
|
1.25 MS/s
|
Single-Ended
|
SAR
|
2.35 V to 5.25 V
|
2.35 V to 5.25 V
|
61 dB
|
- 40 C
|
+ 125 C
|
|
Reel, Cut Tape, MouseReel
|
|
|
|
Analog to Digital Converters - ADC 1x Chip 12-B Data Acquisition S
- LTC1290BIN#PBF
- Analog Devices
-
1:
$97.16
-
35In Stock
|
Mouser Part No
584-LTC1290BIN#PBF
|
Analog Devices
|
Analog to Digital Converters - ADC 1x Chip 12-B Data Acquisition S
|
|
35In Stock
|
|
|
$97.16
|
|
|
$80.01
|
|
|
$75.87
|
|
Min.: 1
Mult.: 1
Max.: 35
|
|
|
LTC1290
|
Through Hole
|
PDIP-20
|
12 bit
|
8 Channel
|
Serial
|
50 kS/s
|
Differential/Single-Ended
|
SAR
|
5 V
|
5 V
|
74 dB
|
- 40 C
|
+ 85 C
|
|
Tube
|
|
|
|
Analog to Digital Converters - ADC 4MSPS 14-bit Dual Differential SAR ADC
- AD7381BCPZ-RL7
- Analog Devices
-
1:
$37.91
-
1,471In Stock
|
Mouser Part No
584-AD7381BCPZ-RL7
|
Analog Devices
|
Analog to Digital Converters - ADC 4MSPS 14-bit Dual Differential SAR ADC
|
|
1,471In Stock
|
|
|
$37.91
|
|
|
$30.84
|
|
|
$29.09
|
|
|
$28.09
|
|
|
View
|
|
|
$24.97
|
|
|
$26.33
|
|
|
$24.97
|
|
|
$24.97
|
|
Min.: 1
Mult.: 1
Max.: 1,471
:
1,500
|
|
|
AD7381
|
SMD/SMT
|
LFCSP-16
|
14 bit
|
2 Channel
|
Serial
|
4 MS/s
|
Differential
|
SAR
|
3 V to 3.6 V
|
3 V to 3.6 V
|
85.4 dB
|
- 40 C
|
+ 125 C
|
|
Reel, Cut Tape, MouseReel
|
|
|
|
Analog to Digital Converters - ADC Isolated 16Bit SigmaDelta ADC Int Clock
- AD7402-8BRIZ
- Analog Devices
-
1:
$9.73
-
380In Stock
|
Mouser Part No
584-AD7402-8BRIZ
|
Analog Devices
|
Analog to Digital Converters - ADC Isolated 16Bit SigmaDelta ADC Int Clock
|
|
380In Stock
|
|
|
$9.73
|
|
|
$7.58
|
|
|
$6.54
|
|
|
$6.37
|
|
|
$6.11
|
|
Min.: 1
Mult.: 1
|
|
|
AD7402
|
SMD/SMT
|
SOIC-8
|
16 bit
|
1 Channel
|
Serial
|
39 kS/s
|
Differential
|
Sigma-Delta
|
5 V
|
3 V to 5.5 V
|
87 dB
|
- 40 C
|
+ 105 C
|
|
Tube
|
|
|
|
Analog to Digital Converters - ADC 16-BIT 5MSPS ADC I.C
- AD7625BCPZ
- Analog Devices
-
1:
$74.57
-
109In Stock
|
Mouser Part No
584-AD7625BCPZ
|
Analog Devices
|
Analog to Digital Converters - ADC 16-BIT 5MSPS ADC I.C
|
|
109In Stock
|
|
|
$74.57
|
|
|
$62.42
|
|
|
$60.12
|
|
|
$56.66
|
|
Min.: 1
Mult.: 1
Max.: 109
|
|
|
AD7625
|
SMD/SMT
|
LFCSP-32
|
16 bit
|
1 Channel
|
Serial
|
6 MS/s
|
Differential
|
SAR
|
|
|
93 dB
|
- 40 C
|
+ 85 C
|
|
Tray
|
|
|
|
Analog to Digital Converters - ADC 18-Bit, 5 MSPS PULSAR Differential ADC
- AD7960BCPZ
- Analog Devices
-
1:
$73.98
-
127In Stock
|
Mouser Part No
584-AD7960BCPZ
|
Analog Devices
|
Analog to Digital Converters - ADC 18-Bit, 5 MSPS PULSAR Differential ADC
|
|
127In Stock
|
|
|
$73.98
|
|
|
$62.35
|
|
|
$59.67
|
|
|
$58.67
|
|
Min.: 1
Mult.: 1
Max.: 127
|
|
|
AD7960
|
SMD/SMT
|
LFCSP-32
|
18 bit
|
1 Channel
|
Serial
|
5 MS/s
|
Differential
|
SAR
|
1.8 V, 5 V
|
1.8 V, 5 V
|
99 dB
|
- 40 C
|
+ 85 C
|
|
Tray
|
|
|
|
Analog to Digital Converters - ADC 10-B, 500ksps ADCs in MS w/ Auto SD
- LTC1197LIS8#PBF
- Analog Devices
-
1:
$9.36
-
312In Stock
|
Mouser Part No
584-LTC1197LIS8#PBF
|
Analog Devices
|
Analog to Digital Converters - ADC 10-B, 500ksps ADCs in MS w/ Auto SD
|
|
312In Stock
|
|
|
$9.36
|
|
|
$7.28
|
|
|
$6.76
|
|
|
$6.18
|
|
|
$5.86
|
|
Min.: 1
Mult.: 1
Max.: 312
|
|
|
LTC1197
|
SMD/SMT
|
SOIC-8
|
10 bit
|
1 Channel
|
Serial
|
250 kS/s
|
Differential/Single-Ended
|
SAR
|
2.7 V to 4 V
|
2.7 V
|
|
- 45 C
|
+ 85 C
|
|
Tube
|
|
|
|
Analog to Digital Converters - ADC 18-Bit, 1Msps 8-Channel Differential 10.24V Input SoftSpan ADC with Wide Input Common Mode Range
- LTC2335ILX-18#PBF
- Analog Devices
-
1:
$58.78
-
245In Stock
|
Mouser Part No
584-LTC2335ILX-18PBF
|
Analog Devices
|
Analog to Digital Converters - ADC 18-Bit, 1Msps 8-Channel Differential 10.24V Input SoftSpan ADC with Wide Input Common Mode Range
|
|
245In Stock
|
|
|
$58.78
|
|
|
$48.45
|
|
|
$45.87
|
|
|
$43.04
|
|
Min.: 1
Mult.: 1
Max.: 245
|
|
|
LTC2335-18
|
SMD/SMT
|
LQFP-48
|
18 bit
|
8 Channel
|
Serial
|
1 MS/s
|
Differential/Pseudo-Differential/Single-Ended
|
SAR
|
5 V
|
5 V
|
96.7 dB
|
- 40 C
|
+ 85 C
|
|
Tray
|
|
|
|
Analog to Digital Converters - ADC 4x, 16-B, 400ksps/ch Diff SoftSpan ADC w
- LTC2344HUH-16#PBF
- Analog Devices
-
1:
$48.15
-
87In Stock
|
Mouser Part No
584-LTC2344HUH-16PBF
|
Analog Devices
|
Analog to Digital Converters - ADC 4x, 16-B, 400ksps/ch Diff SoftSpan ADC w
|
|
87In Stock
|
|
|
$48.15
|
|
|
$40.65
|
|
|
$36.45
|
|
|
$35.45
|
|
Min.: 1
Mult.: 1
Max.: 87
|
|
|
LTC2344-16
|
SMD/SMT
|
QFN-32
|
16 bit
|
4 Channel
|
Serial
|
400 kS/s
|
Differential
|
SAR
|
5 V
|
5 V
|
93.4 dB
|
- 40 C
|
+ 125 C
|
|
Tube
|
|
|
|
Analog to Digital Converters - ADC 16-B, 5Msps SAR ADC
- LTC2385CUH-16#PBF
- Analog Devices
-
1:
$41.30
-
97In Stock
|
Mouser Part No
584-LTC2385CUH-16PBF
|
Analog Devices
|
Analog to Digital Converters - ADC 16-B, 5Msps SAR ADC
|
|
97In Stock
|
|
|
$41.30
|
|
|
$33.75
|
|
|
$30.26
|
|
|
$29.40
|
|
Min.: 1
Mult.: 1
Max.: 97
|
|
|
LTC2385-16
|
SMD/SMT
|
QFN-32
|
16 bit
|
1 Channel
|
Serial
|
5 MS/s
|
Differential
|
SAR
|
2.5 V, 5 V
|
|
|
|
|
|
Tube
|
|
|
|
Analog to Digital Converters - ADC 12-bit dual 3.2-GSP S or single 6.4-GSPS A 595-ADC12DJ3200AAVT
- ADC12DJ3200AAV
- Texas Instruments
-
1:
$2,090.73
-
96In Stock
|
Mouser Part No
595-ADC12DJ3200AAV
|
Texas Instruments
|
Analog to Digital Converters - ADC 12-bit dual 3.2-GSP S or single 6.4-GSPS A 595-ADC12DJ3200AAVT
|
|
96In Stock
|
|
Min.: 1
Mult.: 1
|
|
|
ADC12DJ3200
|
SMD/SMT
|
FCBGA-144
|
12 bit
|
1 Channel/2 Channel
|
Serial
|
3.2 GS/s, 6.4 GS/s
|
Differential/Single-Ended
|
Folding Interpolating
|
1.8 V to 2 V
|
1.05 V to 1.15 V
|
56.6 dB
|
- 40 C
|
+ 85 C
|
|
Tray
|
|
|
|
Analog to Digital Converters - ADC 12B 1MSPS 4x2/2x2 Si mu Sampling SAR A 5 A 595-ADS7223SRHBR
- ADS7223SRHBT
- Texas Instruments
-
1:
$13.83
-
406In Stock
|
Mouser Part No
595-ADS7223SRHBT
|
Texas Instruments
|
Analog to Digital Converters - ADC 12B 1MSPS 4x2/2x2 Si mu Sampling SAR A 5 A 595-ADS7223SRHBR
|
|
406In Stock
|
|
|
$13.83
|
|
|
$10.90
|
|
|
$10.16
|
|
|
$9.36
|
|
|
$8.43
|
|
|
View
|
|
|
$8.40
|
|
|
$8.39
|
|
|
Quote
|
|
Min.: 1
Mult.: 1
:
250
|
|
|
ADS7223
|
SMD/SMT
|
VQFN-32
|
12 bit
|
4 Channel/8 Channel
|
Serial
|
1 MS/s
|
Differential/Pseudo-Differential
|
SAR
|
2.7 V to 5.5 V
|
2.3 V to 5.5 V
|
73 dB
|
- 40 C
|
+ 125 C
|
|
Reel, Cut Tape, MouseReel
|
|
|
|
Analog to Digital Converters - ADC +/-50-mV input prec ision current sensin A 595-AMC3306M05DWER
- AMC3306M05DWE
- Texas Instruments
-
1:
$15.19
-
990In Stock
|
Mouser Part No
595-AMC3306M05DWE
|
Texas Instruments
|
Analog to Digital Converters - ADC +/-50-mV input prec ision current sensin A 595-AMC3306M05DWER
|
|
990In Stock
|
|
|
$15.19
|
|
|
$11.90
|
|
|
$11.07
|
|
|
$10.16
|
|
|
View
|
|
|
$10.06
|
|
|
$9.47
|
|
|
Quote
|
|
Min.: 1
Mult.: 1
|
|
|
AMC3306M05
|
SMD/SMT
|
SOIC-16
|
16 bit
|
4 Channel
|
Serial
|
|
Differential
|
Sigma-Delta
|
|
3.3 V
|
81 dB
|
- 40 C
|
+ 125 C
|
|
Tube
|
|
|
|
Analog to Digital Converters - ADC Single-Supply, Low-Power, Serial 8-Bit A
- MAX1116EKA+T
- Analog Devices / Maxim Integrated
-
1:
$3.61
-
3,823In Stock
|
Mouser Part No
700-MAX1116EKAT
|
Analog Devices / Maxim Integrated
|
Analog to Digital Converters - ADC Single-Supply, Low-Power, Serial 8-Bit A
|
|
3,823In Stock
|
|
|
$3.61
|
|
|
$2.72
|
|
|
$2.50
|
|
|
$2.26
|
|
|
View
|
|
|
$1.90
|
|
|
$2.14
|
|
|
$2.12
|
|
|
$2.01
|
|
|
$1.90
|
|
Min.: 1
Mult.: 1
Max.: 3,823
:
2,500
|
|
|
MAX1116
|
SMD/SMT
|
SOT-23-8
|
8 bit
|
1 Channel
|
Serial
|
100 kS/s
|
Single-Ended
|
SAR
|
|
|
48 dB
|
- 40 C
|
+ 85 C
|
|
Reel, Cut Tape, MouseReel
|
|
|
|
Analog to Digital Converters - ADC 1MSPS Differential Dual ADC
- AD4680BCPZ-RL7
- Analog Devices
-
1:
$30.08
-
1,160In Stock
|
Mouser Part No
584-AD4680BCPZ-RL7
|
Analog Devices
|
Analog to Digital Converters - ADC 1MSPS Differential Dual ADC
|
|
1,160In Stock
|
|
|
$30.08
|
|
|
$24.30
|
|
|
$22.27
|
|
|
$21.18
|
|
|
View
|
|
|
$19.48
|
|
|
$20.77
|
|
|
$20.53
|
|
|
$19.48
|
|
|
$19.48
|
|
Min.: 1
Mult.: 1
Max.: 1,160
:
1,500
|
|
|
AD4680
|
SMD/SMT
|
LFCSP-16
|
16 bit
|
2 Channel
|
Serial
|
1 MS/s
|
Differential
|
SAR
|
3 V to 3.6 V
|
|
100 dB
|
- 40 C
|
+ 125 C
|
|
Reel, Cut Tape, MouseReel
|
|
|
|
Analog to Digital Converters - ADC Power, 16-Bit, 250ksps 1- and 2-Channel ADCs in SOIC
- LTC1864ACS8#PBF
- Analog Devices
-
1:
$20.59
-
951In Stock
|
Mouser Part No
584-LTC1864ACS8#PBF
|
Analog Devices
|
Analog to Digital Converters - ADC Power, 16-Bit, 250ksps 1- and 2-Channel ADCs in SOIC
|
|
951In Stock
|
|
|
$20.59
|
|
|
$16.14
|
|
|
$15.18
|
|
|
$14.25
|
|
|
View
|
|
|
$13.61
|
|
|
$13.37
|
|
Min.: 1
Mult.: 1
|
|
|
LTC1864
|
SMD/SMT
|
SOIC-8
|
16 bit
|
1 Channel
|
Serial
|
250 kS/s
|
Differential/Single-Ended
|
SAR
|
4.75 V to 5.25 V
|
4.75 V to 5.25 V
|
87 dB
|
0 C
|
+ 70 C
|
|
Tube
|
|
|
|
Analog to Digital Converters - ADC 2.35V-5.25V 12 bit 1 MSPS Serial A 595-A A 595-ADS7886SDBVT
- ADS7886SDBVR
- Texas Instruments
-
1:
$4.93
-
1,908In Stock
|
Mouser Part No
595-ADS7886SDBVR
|
Texas Instruments
|
Analog to Digital Converters - ADC 2.35V-5.25V 12 bit 1 MSPS Serial A 595-A A 595-ADS7886SDBVT
|
|
1,908In Stock
|
|
|
$4.93
|
|
|
$3.76
|
|
|
$3.47
|
|
|
$3.14
|
|
|
View
|
|
|
$2.76
|
|
|
$2.99
|
|
|
$2.90
|
|
|
$2.86
|
|
|
$2.76
|
|
Min.: 1
Mult.: 1
:
3,000
|
|
|
ADS7886
|
SMD/SMT
|
SOT-23-6
|
12 bit
|
1 Channel
|
Serial
|
1 MS/s
|
Single-Ended
|
SAR
|
2.35 V to 5.25 V
|
2.35 V to 5.25 V
|
72.25 dB
|
- 40 C
|
+ 125 C
|
|
Reel, Cut Tape, MouseReel
|
|
|
|
Analog to Digital Converters - ADC 400ksps/300ksps, Single-Supply, Low-Powe
- MAX1284BESA+
- Analog Devices / Maxim Integrated
-
1:
$30.74
-
111In Stock
|
Mouser Part No
700-MAX1284BESA
|
Analog Devices / Maxim Integrated
|
Analog to Digital Converters - ADC 400ksps/300ksps, Single-Supply, Low-Powe
|
|
111In Stock
|
|
|
$30.74
|
|
|
$25.64
|
|
|
$23.92
|
|
|
$21.68
|
|
Min.: 1
Mult.: 1
Max.: 111
|
|
|
MAX1284B
|
SMD/SMT
|
SOIC-8
|
12 bit
|
1 Channel
|
Serial
|
400 kS/s
|
Single-Ended
|
SAR
|
|
|
|
- 40 C
|
+ 85 C
|
|
Tube
|
|
South Africa